Rendering 32-bit images - alpha is ignored

I loaded a TGA image with alpha channel used (32-bit color) but for some reason, the alpha channel is ignored when displaying the image. The normal colors are correct, but areas fully transparent (cannot be seen) are all black and fully visible (as if alpha was 255) and the semitransparent areas have the colors drawn as is, but with the alpha at 255. I made sure I set up the BITMAPINFOHEADER struct properly (32 for the .biBitCount value for one), but that didn't work at all. Each pixel has it's own alpha value. I took a screenshot of the original image and what is being displayed, if that helps to explain.

See screenshot

The top window shows my program and the way the image is displayed in it. The bottom is what the original looks like. The checkerboard pattern background indicates transparent areas (for those not familiar with the program). The area in focus is the snow-capped peak with the peak on the furthest left (the short mountain). Note the lack of alpha channel usage in my program for that same area.

How do I get it so I get the alpha channel to be used rather than ignored.

Edit: I'm using DrawDibDraw if that helps.

DrawDibDraw does not provide any means for doing transparency, it doesn't do anything too fancy either.

It is only capable of a simple copy from source to target pixel for pixel.

If you want transparency then use another method, BitBlt?

BitBlt doesn't seem to offer that, by looking at the flags and specifications. There's nothing involving alpha blending or the related that I can see. What do I do to use it to draw the transparent image into the now-working back buffer? I found the AlphaBlend function, but in attempting to use it, I get "unresolved external symbols" and when adding the library, a DLL file, it says that it can't be found (Msimg32.dll). There's no "lib" file mentioned.

Link with msimg32.lib and use AlphaBlend me thinks.

Okay, that's resolved, but now comes a new problem, a very weird one. I took another screenshot showing it.

Here's a screenshot showing the effect (and some of the related code).

This is the other part of the code, that of the AlphaUsage struct:

Code:

---

AlphaUsage.BlendOp = 0; // using AC_SRC_OVER has the same effect
AlphaUsage.BlendFlags = 0;
AlphaUsage.SourceConstantAlpha = 255;
AlphaUsage.AlphaFormat = AC_SRC_ALPHA;

---

The screenshot says a lot about the effects I'm seeing. If I move the window out of the center area, the bluish haze is not there and the "copying" of my test image (my logo as I call it) disappears, but when moved back or while the window remains in the center, this bluish haze and copying effect occur. If I move the logo up more off screen, less of the logo is displayed in the "copy effect". Below the bottom area where the image is to be drawn to, the "copy effect" does not occur, but the blue haze is still present. None of the warnings are related to the area where this is occurring (they occur from each usage of fopen, strcpy, sprintf, and other common C-based functions)).

Edit: I used "The GIMP" to simulate the effects of what I should be seeing. This is what I should be seeing in the actual window. Of course, the final result will have more detail than this as there's the hills, sky fade, ground, some houses, and text on the black sides in addition to what I have so far.

Maybe the warnings have something to do with your incorrectly using C functions in C++?

Perhaps some BlendFlags are needed? I have no idea really, GDI is not my thing (even though I do understand it, doesn't mean im that good at it ;))

The documentation says that "BlendFlags" must be zero. I can't get the search box on MSDN's website and any typing I do tends to cause Firefox to use it's quick search feature.

AlphaBlend() will do want you want, however it does not support any scaling. What you need to do is make a mask of each of your bitmaps. You then blit them like this:

Code:

---

...
if (pImage)
{
  CBitmap *pPrevMem=(CBitmap *)pTempDC->SelectObject(pMask);
         
  //Perform transparent stretch blit
  m_pMemoryDC->StretchBlt( iX, iY, iTileW, iTileH, pTempDC,
                        0, 0, iOTileW,iOTileH,SRCAND);
           
  pTempDC->SelectObject(pPrevMem);
  pPrevMem=(CBitmap *)pTempDC->SelectObject(pImage);

  // Note the use of SRCPAINT rather than SRCCOPY.
  m_pMemoryDC->StretchBlt(iX, iY, iTileW, iTileH, pTempDC,
        0, 0,iOTileW,iOTileH,SRCPAINT);
             
  pTempDC->SelectObject(pPrevMem);
}
...

---

There is a lot of information on the internet concerning this. My PrepareMask() function inside of CTileGDI is nearly straight from CodeGuru's forum example.

This means you will be blitting two images per bitmap, but it really is the only way to do this if you want scaling support. There is no way to get a pointer to the buffer in GDI so you cannot manually plot pixels without going through the DC's function. This evaluates to 1 function call per pixel and is much slower than just using this method.

There are a lot of things left unexplained in that code and I cannot possibly explain my entire GDI tile rendering system to you in one post.

Remember that each DC must have a bitmap or it will not work.

Scaling (or stretching as I call it) isn't anything I need. Scaling, to me, is distance and size put in one. Mountains would have high scaling, like 2000, meaning each pixel is 2000 pixels at a scaling value of 1 and something like 60,000 feet distant (depending on the field of view used). I just need a direct draw onto the back buffer. I also happen to know the formula for calculating the resulting color, a formula I've known since 2002 (this is the main version), well before I got into programming.

You're apparently missing something. As I have it, AlphaBlend is giving weird results. I'm not stretching anything, just drawing the entire image as is at normal size into a location determined by variables (XMain and YMain) my program will change relative to the speed and scaling values used (120 mph and a scaling of 900 would mean the image position changes one pixel every 3/4 second). I just need it to draw the image as is into the back buffer in order of back to front (highest to lowest scaling value), of which BitBlt brings it to the screen buffer.

Also can I ask why you've chosen MFC over plain Win32 for a game?

No, no, no. I'm doing exactly the same. Loading a TGA file type 2 32 bits, and use AlphaBlend to draw it. It just works. You only need this:
(fragment from my code)

Code:

---

void TGA2_32::draw(HDC hDC, int x, int y, unsigned char alpha)
{
    if(!this->hBmp) return;
   
    HDC hMemDC = CreateCompatibleDC(hDC);
    SelectObject(hMemDC, this->hBmp);
    BLENDFUNCTION bf;
    bf.AlphaFormat = 1;
    bf.BlendOp = AC_SRC_OVER;
    bf.SourceConstantAlpha = alpha;
    bf.BlendFlags = 0;
    AlphaBlend(hDC, x, y, this->nWidth, this->nHeight, hMemDC,
                    0, 0, this->nWidth, this->nHeight, bf);
    DeleteDC(hMemDC);
}

---

The "AlphaFormat=1" is only because AC_SRC_ALPHA is not defined in my version of the gdi header, and I found it should be 1.

What you probably forgot, is doing premultiplying.

That is, after you loaded the pixel data, you set:
R to (R*A/255)
G to (G*A/255)
B to (B*A/255)

That is needed for the AlphaBlend function to work correctly.

My advice: get rid of your "DrawDibDraw" thing, drawing bitmaps with plain Win32 functions is easy enough.

Quote:

---

Originally Posted by Bubba

AlphaBlend() will do want you want, however it does not support any scaling.

---

Yes it does. Why anyway do you think it takes two height parameters and two width parameters?

I tested it, and it scaled/stretched well. The only thing AlphaBlend does not support is mirroring.

@zacs7:

Quote:

---

Also can I ask why you've chosen MFC over plain Win32 for a game?

---

What do you mean by this? What's the difference? Around November or so, I, at the MSN Newsgroups, was told about using DrawDibDraw as it was the fastest thing that didn't use DirectX. I don't want to use DirectX.

What's wrong with using DrawDibDraw anyway? For images without alpha, it's worth using, unless you explain what's wrong with using DrawDibDraw.

I tried premultiplying, but it gives the exact same result as in my screenshot (the haze and the "copy effect"). This is in my LoadFile function:

Code:

---

                while (ArrayIndex < BMPInfo->biSizeImage) // premultiplies the colors for alphablend to work
                {
                        NewColor = (float)BMPData[ArrayIndex]*(float)BMPData[ArrayIndex+3]/255.0+0.5;
                        BMPData[ArrayIndex] = (unsigned char)NewColor;
                        NewColor = (float)BMPData[ArrayIndex+1]*(float)BMPData[ArrayIndex+3]/255.0+0.5;
                        BMPData[ArrayIndex+1] = (unsigned char)NewColor;
                        NewColor = (float)BMPData[ArrayIndex+2]*(float)BMPData[ArrayIndex+3]/255.0+0.5;
                        BMPData[ArrayIndex+2] = (unsigned char)NewColor;
                        ArrayIndex += 4;
                }

---

NewColor is a float. BMPData is an unsigned char. ArrayIndex is an unsigned int (since arrays can't have negative index values). The adding of 0.5 is for rounding purposes. Multiplying 255 by 255 in a char would cause variable overflow and thus the reason for using a float. A short could also work but is less precise. TGAs are read in BGRA order so the loop is doing the blue first referencing the alpha 3 array index values higher. Either way, the result is exactly the same as before.

Edit: I tried using BitBlt to copy, paint, and invert pixels and wow do I get weird results. From using this in that same area without AlphaBlend or DrawDibDraw (commented out):

BitBlt(HDCBack, Mountains.XMain, Mountains.YMain, MountainsInfo.biWidth, MountainsInfo.biHeight, HDCScreen, MountainsInfo.biWidth, MountainsInfo.biHeight, SRCCOPY);

I get what is shown in this screenshot. Could this be due to BitBlt being unable to draw 32-bit or is it because there's something wrong with the data (DrawDibDraw displays it just fine). Premultiplying it yields the exact same scene. SRCPAINT gives a brighter area in the center and SRCINVERT gives a darker area in the center, but is monotonic like this without any resemblance of looking like mountains.

Edit #2: Another big clue found. I messed around with the BLENDFUNCTION structure and found some other clues. I took some notes and found an interesting, but bizarre, pattern. On black (HTML color 000000), it renders as white (HTML color FFFFFF). On a background of 2060F0 (a bluish color, based on HTML RGB notation rather than BGR), it draws as 40C0FF. Near the bottom part of this, due to the copy effect, it draws as 60FFFF. On a A0A8B0 background, it draws as C0FFFF and for the copy effect, as E0FFFF. The red value seems to be adding 32, the green either doubling or adding 96, and the blue being set to 255 or something else. Strangely enough, that very closely matches the pixel in the top left corner to which the image is to be drawn on (compare 2060FF and 2060F0, strikingly similar). I checked the premultiplication stuff and it makes complete sense. The pixel at 0, 46 (in my image edittor) has the color of (166, 154, 150, 128) in RGBA order. My debug test shows it as 150, 154, 166, and 128 before premultiplication and 75, 77, 83, 128 after it which is exactly what I expected. Why is it doing this? Why isn't any image being displayed? What is with the copying down and to the right anomaly? Only DrawDibDraw actually displays anything in the way of an image, only without the alpha computation.

If you want to get it to work, you could first try it with plain Win32 API. I know that that can work correctly and I know exactly the way, so that's why I recommend you to try that first.

You need to explain to me what the difference is. Plain Win32 API doesn't mean anything to me as I'm using Windows functions as AlphaBlend and DrawDibDraw are both things in the Windows SDK. Please explain this.

Also, I editted my previous message with more clues I found.

Quote:

---

Originally Posted by ulillillia

I loaded a TGA image with alpha channel used (32-bit color)

---

Can you show the code that does this? Exactly how is the BMPInfo and BMP data getting filled out? All the basic calls look right, so I'm suspecting bogus or corrupted data somewhere.

Ok, I didn't know that DrawDib was also standard Win32, but what I mean is only using the standard GDI functions declared in wingdi.h and (some of them) defined in msimg32.lib.
I don't know if that's correct, but try to stick to functions like AlphaBlend, CreateDIBitmap(), nothing that has to do with "DrawDib", to see if it does work with just GDI.

Well, I apparently need to post everything related to it....

Code:

---

struct SceneryData
{
        int XMain; // base integer X position
        int YMain; // base integer Y position
        double x; // actual X position
        double y; // actual Y position
        double Scaling; // background scaling (distance)
};

BLENDFUNCTION AlphaUsage; // the blend function

unsigned char MountainsData[524288]; // The mountains background (1024x128 image at 32-bit color)
LPVOID MountainsDataPointer;
BITMAPINFOHEADER MountainsInfo;
LPBITMAPINFOHEADER MountainsInfoPointer;
struct SceneryData Mountains;

FILE *FileHandle; // handle for reading/writing files

char LoadFile(const char FileName[64], char FileType, BITMAPINFOHEADER *BMPInfo, unsigned char *BMPData)
{
        char BasePath[128]; // the base path, that of which started from
        char FullFileName[192]; // the full path combining the base path and the parameter
        unsigned int ArrayIndex = 0;
        float NewColor = 0;
       
        strcpy(BasePath, "C:\\My Documents\\My programs\\Interactive Animation\\"); // get the obvious base path first
        sprintf(FullFileName, "%s%s", BasePath, FileName); // combine the base path and file name
        FileHandle = fopen(FullFileName, "rb"); // read the source file to display, binary mode
       
        // FileHandle = fopen(FileName, "rb"); // read the source file to display, binary mode
       
        // skip first 18 bytes for TGA then read in BGRA format
       
        if (FileHandle == 0) // if the file can't be found
        {
                return 1; // indicates an error occurred
        }
       
        if (FileType == 1) // reading a BMP file
        {
                fseek(FileHandle, 14, SEEK_SET); // skip the basic file header data but read from the info header
                fread(&BMPInfo->biSize, 4, 1, FileHandle); // bytes 0E through 11
                fread(&BMPInfo->biWidth, 4, 1, FileHandle); // 12 through 15
                fread(&BMPInfo->biHeight, 4, 1, FileHandle); // 16 through 19
                fread(&BMPInfo->biPlanes, 2, 1, FileHandle); // 1A and 1B
                fread(&BMPInfo->biBitCount, 2, 1, FileHandle); // 1C and 1D
                fread(&BMPInfo->biCompression, 4, 1, FileHandle); // 1E through 21
                fread(&BMPInfo->biSizeImage, 4, 1, FileHandle); // 22 through 25
                fread(&BMPInfo->biXPelsPerMeter, 4, 1, FileHandle); // 26 through 29
                fread(&BMPInfo->biYPelsPerMeter, 4, 1, FileHandle); // 2A through 2D
                fread(&BMPInfo->biClrUsed, 4, 1, FileHandle); // 2E through 31
                fread(&BMPInfo->biClrImportant, 4, 1, FileHandle); // 32 through 35
                fread(BMPData, 1, BMPInfo->biSizeImage, FileHandle); // read the main image data // reads in BGR format
        }
       
        if (FileType == 2) // reading a TGA file
        {
                fseek(FileHandle, 12, SEEK_SET); // skip the basic file header data but read from the info header
                BMPInfo->biSize = 40; // the size of the struct, always 40 in my case (due to true color being used)
                fread(&BMPInfo->biWidth, 2, 1, FileHandle); // image width, 2 bytes in the case of TGAs
                fread(&BMPInfo->biHeight, 2, 1, FileHandle); // image height, 2 bytes in the case of TGAs
                BMPInfo->biPlanes = 1; // always 1
                BMPInfo->biBitCount = 32; // number of bits per pixel, always to be 32 for TGA images (due to alpha channel)
                BMPInfo->biCompression = BI_RGB; // no compression used
                BMPInfo->biSizeImage = BMPInfo->biWidth*BMPInfo->biHeight*4; // width times height times bitcount divided by 8 gives the image data size
                BMPInfo->biXPelsPerMeter = 2835; // resolution in pixels per meter
                BMPInfo->biYPelsPerMeter = 2835;
                BMPInfo->biClrUsed = 0; // always 0 in my case
                BMPInfo->biClrImportant = 0; // same here
                fseek(FileHandle, 18, SEEK_SET); // skip to the main image data
                fread(BMPData, 1, BMPInfo->biSizeImage, FileHandle); // read the main image data // reads in BGRA format
               
                if (DebugTest[0] == 0) // Wow!  It's a test!
                {
                        DebugTest[1] = (int)BMPData[331776]; // the pixel at 0, 46 in The GIMP in the TGA image to be opened
                        DebugTest[2] = (int)BMPData[331777];
                        DebugTest[3] = (int)BMPData[331778];
                        DebugTest[4] = (int)BMPData[331779];
                }
               
                while (ArrayIndex < BMPInfo->biSizeImage) // premultiplies the colors for alphablend to work
                {
                        /*
                        BMPData[ArrayIndex] = BMPData[ArrayIndex] * BMPData[ArrayIndex+3] / 255;
                        BMPData[ArrayIndex+1] = BMPData[ArrayIndex+1] * BMPData[ArrayIndex+3] / 255;
                        BMPData[ArrayIndex+2] = BMPData[ArrayIndex+2] * BMPData[ArrayIndex+3] / 255;
                        */
                       
                        NewColor = (float)BMPData[ArrayIndex]*(float)BMPData[ArrayIndex+3]/255.0+0.5;
                        BMPData[ArrayIndex] = (unsigned char)NewColor;
                        NewColor = (float)BMPData[ArrayIndex+1]*(float)BMPData[ArrayIndex+3]/255.0+0.5;
                        BMPData[ArrayIndex+1] = (unsigned char)NewColor;
                        NewColor = (float)BMPData[ArrayIndex+2]*(float)BMPData[ArrayIndex+3]/255.0+0.5;
                        BMPData[ArrayIndex+2] = (unsigned char)NewColor;
                        ArrayIndex += 4;
                }
               
                if (DebugTest[0] == 0) // Nice, anyone for a test?
                {
                        DebugTest[0] = 1; // so this test is processed only once
                        DebugTest[5] = (int)BMPData[331776]; // the same pixel, but after premultiplication is applied
                        DebugTest[6] = (int)BMPData[331777];
                        DebugTest[7] = (int)BMPData[331778];
                        DebugTest[8] = (int)BMPData[331779];
                       
                        sprintf(DebugDetails, "The previous color values were %d %d %d %d.\nThe new color values are %d %d %d %d.", DebugTest[1], DebugTest[2], DebugTest[3], DebugTest[4], DebugTest[5], DebugTest[6], DebugTest[7], DebugTest[8]); // for debugging
                        MessageBox(hwnd, DebugDetails, "Debug Results", MB_OK);
                }
        }
       
        fclose(FileHandle); // close the file releasing the handle
       
        return 0;
}

void InitiateObjectPositions()
{
        Logo.x = 0.0;
        Logo.y = 64.0;
        Logo.Scaling = 1.0;
        Mountains.x = 4.0;
        Mountains.XMain = 4;
        Mountains.y = 116.0;
        Mountains.YMain = 116;
        Mountains.Scaling = 1125;
}

void InitializeDrawing()
{
        HDCScreen = GetDC(hwnd); // set the screen buffer DC
        HDCBack = CreateCompatibleDC(HDCScreen); // create a compatible DC, of which is to be used for drawing into the back buffer
        HBMPBack = CreateCompatibleBitmap(HDCScreen, 800, 600); // create compatible bitmap, used for drawing into, but not on screen
        SelectObject(HDCBack, HBMPBack); // select the created bitmap
        ImageHandle = DrawDibOpen(); // set the DrawDib DC handle
        AlphaUsage.BlendOp = 0;
        AlphaUsage.BlendFlags = 0;
        AlphaUsage.SourceConstantAlpha = 255;
        AlphaUsage.AlphaFormat = AC_SRC_ALPHA;
       
        ... // unrelated code for setting up front and back buffers' BITMAPINFOHEADER structures
}

void DrawScenery()
{
        /* This function renders and displays the scene.
        Rules:
       
        *  The entire area must be filled, no gaps nor exceptions (the side and sky objects do this)
        *  The scene must be ordered so that it is drawn back to front.
        *  The scene should tile when neccessary cropping it so that it doesn't exceed the interior window area.
        *  Use for loops for repeated drawing of the same image.
        *  Draw into the back buffer then blit it into the front buffer before actually drawing the scene.
        */
       
        DrawDibDraw(ImageHandle, HDCBack, 0, 0, SkyBGInfo.biWidth, SkyBGInfo.biHeight, SkyBGInfoPointer, SkyBGDataPointer, 0, 0, SkyBGInfo.biWidth, SkyBGInfo.biHeight, 0);
        DrawDibDraw(ImageHandle, HDCBack, 0, 240, FogInfo.biWidth, FogInfo.biHeight, FogInfoPointer, FogDataPointer, 0, 0, FogInfo.biWidth, FogInfo.biHeight, 0);
        // DrawDibDraw(ImageHandle, HDCBack, Mountains.XMain, Mountains.YMain, MountainsInfo.biWidth, MountainsInfo.biHeight, MountainsInfoPointer, MountainsDataPointer, 0, 0, MountainsInfo.biWidth, MountainsInfo.biHeight, 0);
        // BitBlt(HDCBack, Mountains.XMain, Mountains.YMain, MountainsInfo.biWidth, MountainsInfo.biHeight, HDCScreen, MountainsInfo.biWidth, MountainsInfo.biHeight, SRCCOPY); // just another old-fashioned test
        AlphaBlend(HDCBack, Mountains.XMain, Mountains.YMain, MountainsInfo.biWidth, MountainsInfo.biHeight, HDCScreen, 0, 0, MountainsInfo.biWidth, MountainsInfo.biHeight, AlphaUsage);
        DrawDibDraw(ImageHandle, HDCBack, Logo.XMain, Logo.YMain, LogoInfo.biWidth, LogoInfo.biHeight, LogoInfoPointer, LogoDataPointer, 0, 0, LogoInfo.biWidth, LogoInfo.biHeight, 0);
        DrawDibDraw(ImageHandle, HDCBack, 640, 0, RightSidePanelInfo.biWidth, RightSidePanelInfo.biHeight, RightSidePanelInfoPointer, RightSidePanelDataPointer, 0, 0, RightSidePanelInfo.biWidth, RightSidePanelInfo.biHeight, 0);
        DrawDibDraw(ImageHandle, HDCBack, 0, 480, BottomSidePanelInfo.biWidth, BottomSidePanelInfo.biHeight, BottomSidePanelInfoPointer, BottomSidePanelDataPointer, 0, 0, BottomSidePanelInfo.biWidth, BottomSidePanelInfo.biHeight, 0);
       
        BitBlt(HDCScreen, 0, 0, WindowSizeBase.x, WindowSizeBase.y, HDCBack, 0, 0, SRCCOPY); // swaps the back and front buffers for displaying
}

// in the main windows function:

        DebugTest[0] = 0; // set up for debugging stuff to prevent message boxes from appearing nonstop without end
        InitializeDrawing(); // set up HDC's, front and back buffers, and alpha blend details
       
        LoadFile("Logo.bmp", 1, &LogoInfo, &LogoData);
        LogoInfoPointer = &LogoInfo;
        LogoDataPointer = &LogoData;
        LoadFile("SkyBG.bmp", 1, &SkyBGInfo, &SkyBGData);
        SkyBGInfoPointer = &SkyBGInfo;
        SkyBGDataPointer = &SkyBGData;
        LoadFile("Fog.bmp", 1, &FogInfo, &FogData);
        FogInfoPointer = &FogInfo;
        FogDataPointer = &FogData;
        LoadFile("MountainsBG.tga", 2, &MountainsInfo, &MountainsData);
        MountainsInfoPointer = &MountainsInfo;
        MountainsDataPointer = &MountainsData;
        LoadFile("RightSidePanel.bmp", 1, &RightSidePanelInfo, &RightSidePanelData);
        RightSidePanelInfoPointer = &RightSidePanelInfo;
        RightSidePanelDataPointer = &RightSidePanelData;
        LoadFile("BottomSidePanel.bmp", 1, &BottomSidePanelInfo, &BottomSidePanelData);
        BottomSidePanelInfoPointer = &BottomSidePanelInfo;
        BottomSidePanelDataPointer = &BottomSidePanelData;
       
        InitiateObjectPositions(); // sets positions for the objects
       
        while(GameRunning == 1) // this is the main loop
        {
                PeekMessage(&msg,hwnd,NULL,NULL,PM_REMOVE);
                if (msg.message == WM_QUIT) // check for a quit message
                {
                        GameRunning = 0; // if found, quit app
                        break;
                }
               
                else
                {
                        // At the start of each frame, the clock is advanced as close as possible to 1/60 of a second.
                        AdvanceClock();

                        // Next, keyboard input should be processed
                        ProcessInput();
                       
                        // After that, the positions of the objects are processed
                        MoveObjects();

                        // Then, the scene must be drawn
                        DrawScenery();
                       
                        // Finally, translate and dispatch any Windows messages into event queue
                        TranslateMessage(&msg);
                        DispatchMessage(&msg);
                }
        }
       
        // free up handles and other resources
        DrawDibClose(ImageHandle); // free the resources
        ReleaseDC(hwnd, HDCScreen); // free the DC handles
        DeleteDC(HDCBack);
        DeleteObject(HBMPBack);
}

---

Yeah, it's a lot of code, but it appears as if I need to post this much. Unrelated code and functions are left out. Heh, if it helps, I'll even post the image in question. Download the ZIP file containing the TGA here. All other files are BMPs and they display perfectly fine with DrawDibDraw. Since the thread has gone on to page 2, I figured I'd post the results I'm seeing and this is the best screenshot I've uploaded showing the effects very clearly. If it helps, this is what I should be seeing (as a simulated screenshot, created through a simple modification in The GIMP).

Quote:

---

Originally Posted by ulillillia

Code:

---

                fread(&BMPInfo->biWidth, 2, 1, FileHandle); // image width, 2 bytes in the case of TGAs
                fread(&BMPInfo->biHeight, 2, 1, FileHandle); // image height, 2 bytes in the case of TGAs

---

---

This is a problem. The biWidth and biHeight fields are LONG variables, but you're only reading 2 bytes into them. The high bytes remain uninitialized. You make the same mistake in the BMP loader as well.

The funny repetitive effect you are seeing is a pretty typical symptom of having corrupted values.

Also, you should never read multi-byte quantities directly into memory. In the case of TGA you got lucky because the values are little-endian and so is your machine. But this is not guaranteed to be the case. Instead, you should read each byte of the multi-byte quantity and pack the bytes into an integer as appropriate to their endianness.

Okay, so I made the changes and now the TGA isn't being displayed at all. The BMPs, however, are displaying perfectly fine. What else is wrong?

Code:

---

// updated LoadFile function

char LoadFile(const char FileName[64], char FileType, BITMAPINFOHEADER *BMPInfo, unsigned char *BMPData)
{
        char BasePath[128]; // the base path, that of which started from
        char FullFileName[192]; // the full path combining the base path and the parameter
        unsigned int ArrayIndex = 0;
        float NewColor = 0;
        unsigned char ValuesBase[4]; // for fixing endianness
       
        strcpy(BasePath, "C:\\My Documents\\My programs\\Interactive Animation\\"); // get the obvious base path first
        sprintf(FullFileName, "%s%s", BasePath, FileName); // combine the base path and file name
        FileHandle = fopen(FullFileName, "rb"); // read the source file to display, binary mode
       
        // FileHandle = fopen(FileName, "rb"); // read the source file to display, binary mode
       
        // skip first 18 bytes for TGA then read in BGRA format
       
        if (FileHandle == 0) // if the file can't be found
        {
                return 1; // indicates an error occurred
        }
       
        if (FileType == 1) // reading a BMP file
        {
                fseek(FileHandle, 14, SEEK_SET); // skip the basic file header data but read from the info header
                fread(&ValuesBase, 1, 4, FileHandle); // bytes 0E through 11
                BMPInfo->biSize = (DWORD)ValuesBase[0]+(DWORD)ValuesBase[1]*256+(DWORD)ValuesBase[2]*65536+(DWORD)ValuesBase[3]*16777216;
                fread(&ValuesBase, 1, 4, FileHandle); // bytes 0E through 11
                BMPInfo->biWidth = (long)ValuesBase[0]+(long)ValuesBase[1]*256+(long)ValuesBase[2]*65536+(long)ValuesBase[3]*16777216;
                fread(&ValuesBase, 1, 4, FileHandle); // bytes 0E through 11
                BMPInfo->biHeight = (long)ValuesBase[0]+(long)ValuesBase[1]*256+(long)ValuesBase[2]*65536+(long)ValuesBase[3]*16777216;
                fread(&ValuesBase, 1, 2, FileHandle); // bytes 0E through 11
                BMPInfo->biPlanes = (WORD)ValuesBase[0]+(WORD)ValuesBase[1]*256;
                fread(&ValuesBase, 1, 2, FileHandle); // bytes 0E through 11
                BMPInfo->biBitCount = (WORD)ValuesBase[0]+(WORD)ValuesBase[1]*256;
                fread(&ValuesBase, 1, 4, FileHandle); // bytes 0E through 11
                BMPInfo->biCompression = (DWORD)ValuesBase[0]+(DWORD)ValuesBase[1]*256+(DWORD)ValuesBase[2]*65536+(DWORD)ValuesBase[3]*16777216;
                fread(&ValuesBase, 1, 4, FileHandle); // bytes 0E through 11
                BMPInfo->biSizeImage = (DWORD)ValuesBase[0]+(DWORD)ValuesBase[1]*256+(DWORD)ValuesBase[2]*65536+(DWORD)ValuesBase[3]*16777216;
                fread(&ValuesBase, 1, 4, FileHandle); // bytes 0E through 11
                BMPInfo->biXPelsPerMeter = (long)ValuesBase[0]+(long)ValuesBase[1]*256+(long)ValuesBase[2]*65536+(long)ValuesBase[3]*16777216;
                fread(&ValuesBase, 1, 4, FileHandle); // bytes 0E through 11
                BMPInfo->biYPelsPerMeter = (long)ValuesBase[0]+(long)ValuesBase[1]*256+(long)ValuesBase[2]*65536+(long)ValuesBase[3]*16777216;
                fread(&ValuesBase, 1, 4, FileHandle); // bytes 0E through 11
                BMPInfo->biClrUsed = (DWORD)ValuesBase[0]+(DWORD)ValuesBase[1]*256+(DWORD)ValuesBase[2]*65536+(DWORD)ValuesBase[3]*16777216;
                fread(&ValuesBase, 1, 4, FileHandle); // bytes 0E through 11
                BMPInfo->biClrImportant = (DWORD)ValuesBase[0]+(DWORD)ValuesBase[1]*256+(DWORD)ValuesBase[2]*65536+(DWORD)ValuesBase[3]*16777216;
                fread(BMPData, 1, BMPInfo->biSizeImage, FileHandle); // read the main image data // reads in BGR format
               
                /*
                fread(&BMPInfo->biSize, 4, 1, FileHandle); // bytes 0E through 11
                fread(&BMPInfo->biWidth, 4, 1, FileHandle); // 12 through 15
                fread(&BMPInfo->biHeight, 4, 1, FileHandle); // 16 through 19
                fread(&BMPInfo->biPlanes, 2, 1, FileHandle); // 1A and 1B
                fread(&BMPInfo->biBitCount, 2, 1, FileHandle); // 1C and 1D
                fread(&BMPInfo->biCompression, 4, 1, FileHandle); // 1E through 21
                fread(&BMPInfo->biSizeImage, 4, 1, FileHandle); // 22 through 25
                fread(&BMPInfo->biXPelsPerMeter, 4, 1, FileHandle); // 26 through 29
                fread(&BMPInfo->biYPelsPerMeter, 4, 1, FileHandle); // 2A through 2D
                fread(&BMPInfo->biClrUsed, 4, 1, FileHandle); // 2E through 31
                fread(&BMPInfo->biClrImportant, 4, 1, FileHandle); // 32 through 35
                fread(BMPData, 1, BMPInfo->biSizeImage, FileHandle); // read the main image data // reads in BGR format
                */
        }
       
        if (FileType == 2) // reading a TGA file
        {
                fseek(FileHandle, 12, SEEK_SET); // skip the basic file header data but read from the info header
                BMPInfo->biSize = 40; // the size of the struct, always 40 in my case (due to true color being used)
                fread(&ValuesBase, 1, 2, FileHandle);
                BMPInfo->biWidth = (long)ValuesBase[0]+(long)ValuesBase[1]*256; // only two bytes are read for TGAs
                fread(&ValuesBase, 1, 2, FileHandle);
                BMPInfo->biWidth = (long)ValuesBase[0]+(long)ValuesBase[1]*256; // only two bytes are read for TGAs
               
                // fread(&BMPInfo->biWidth, 2, 1, FileHandle); // image width, 2 bytes in the case of TGAs
                // fread(&BMPInfo->biHeight, 2, 1, FileHandle); // image height, 2 bytes in the case of TGAs
                BMPInfo->biPlanes = 1; // always 1
                BMPInfo->biBitCount = 32; // number of bits per pixel, always to be 32 for TGA images (due to alpha channel)
                BMPInfo->biCompression = BI_RGB; // no compression used
                BMPInfo->biSizeImage = BMPInfo->biWidth*BMPInfo->biHeight*4; // width times height times bitcount divided by 8 gives the image data size
                BMPInfo->biXPelsPerMeter = 2835; // resolution in pixels per meter
                BMPInfo->biYPelsPerMeter = 2835;
                BMPInfo->biClrUsed = 0; // always 0 in my case
                BMPInfo->biClrImportant = 0; // same here
                fseek(FileHandle, 18, SEEK_SET); // skip to the main image data
                fread(BMPData, 1, BMPInfo->biSizeImage, FileHandle); // read the main image data // reads in BGRA format
               
                if (DebugTest[0] == 0) // Wow!  It's a test!
                {
                        DebugTest[1] = (int)BMPData[331776];
                        DebugTest[2] = (int)BMPData[331777];
                        DebugTest[3] = (int)BMPData[331778];
                        DebugTest[4] = (int)BMPData[331779];
                }
               
                while (ArrayIndex < BMPInfo->biSizeImage) // premultiplies the colors for alphablend to work
                {
                        /*
                        BMPData[ArrayIndex] = BMPData[ArrayIndex] * BMPData[ArrayIndex+3] / 255;
                        BMPData[ArrayIndex+1] = BMPData[ArrayIndex+1] * BMPData[ArrayIndex+3] / 255;
                        BMPData[ArrayIndex+2] = BMPData[ArrayIndex+2] * BMPData[ArrayIndex+3] / 255;
                        */
                       
                        NewColor = (float)BMPData[ArrayIndex]*(float)BMPData[ArrayIndex+3]/255.0+0.5;
                        BMPData[ArrayIndex] = (unsigned char)NewColor;
                        NewColor = (float)BMPData[ArrayIndex+1]*(float)BMPData[ArrayIndex+3]/255.0+0.5;
                        BMPData[ArrayIndex+1] = (unsigned char)NewColor;
                        NewColor = (float)BMPData[ArrayIndex+2]*(float)BMPData[ArrayIndex+3]/255.0+0.5;
                        BMPData[ArrayIndex+2] = (unsigned char)NewColor;
                        ArrayIndex += 4;
                }
               
                if (DebugTest[0] == 0) // Nice, anyone for a test?
                {
                        DebugTest[0] = 1; // so this test is processed only once
                        DebugTest[5] = (int)BMPData[331776];
                        DebugTest[6] = (int)BMPData[331777];
                        DebugTest[7] = (int)BMPData[331778];
                        DebugTest[8] = (int)BMPData[331779];
                       
                        sprintf(DebugDetails, "The previous color values were %d %d %d %d.\nThe new color values are %d %d %d %d.", DebugTest[1], DebugTest[2], DebugTest[3], DebugTest[4], DebugTest[5], DebugTest[6], DebugTest[7], DebugTest[8]); // for debugging
                        MessageBox(hwnd, DebugDetails, "Debug Results", MB_OK);
                }
        }
       
        fclose(FileHandle); // close the file releasing the handle
       
        return 0;
}

---

I've only seen little endian. I've never seen big endian. I know it's processor-related, but what CPUs use big endian? 4080 in little endian, as an unsigned short, is 32832, but as big endian, it's 16512 instead, a huge difference.

Edit: I noticed that I had the biWidth value specified twice for some odd reason. Then again, fixing that, I'm still getting the exact same effects - the copy effect. So now what's wrong?

Edit #2: Even specifying the width and height directly into the function, it still happens. This leaves either the structure or the two HDC's. It's unlikely the HDC's since DrawDibDraw uses them and BitBlt also does and no problems occur with either of these.

Code:

---

        AlphaUsage.BlendOp = AC_SRC_OVER;
        AlphaUsage.BlendFlags = 0;
        AlphaUsage.SourceConstantAlpha = 255;
        AlphaUsage.AlphaFormat = AC_SRC_ALPHA;
       
        AlphaBlend(HDCBack, 8, 8, 1024, 128, HDCScreen, 0, 0, 1024, 128, AlphaUsage);

---

With this, pretty much everything is ruled out as problematic except these two areas. The copy effect recurs every 8 pixels right and down given this. There must be something wrong in this area. Both HDCBack (the back buffer being drawn into) and HDCScreen (the front buffer to be drawn to the screen) show nonzero values when using the debug things indicating that they are valid. This leaves only the structure as faulty, but I don't see anything wrong.

I don't think this really helps, but first try to simplify your loading function:

- First support for example only type 2, 32bpp.

- You're reading from offset to offset, I also did this at first, but it makes your code pretty large and harder to read. You can put the header data you need in a struct, like this:

Code:

---

struct TGAHEADER
{
        unsigned char  cIdentificationField;
        bool          bMapIncluded;
        unsigned char  cTgaType;
        char          cIgnore[9];
        short          iWidth;
        short          iHeight;
        unsigned char  cBpp;
        unsigned char  cImageDescriptor;
};

---

Try to make the function as small as possible, you can expand it later on. This makes it easier to see if there's any error in it.

Just in case: the image is not runlength encoded I hope? (sorry, a bit stupid:P)

But, more important, you have this code twice:

Code:

---

                fread(&ValuesBase, 1, 2, FileHandle);
                BMPInfo->biWidth = (long)ValuesBase[0]+(long)ValuesBase[1]*256; // only two bytes are read for TGAs
                fread(&ValuesBase, 1, 2, FileHandle);
                BMPInfo->biWidth = (long)ValuesBase[0]+(long)ValuesBase[1]*256; // only two bytes are read for TGAs

---

Instead of reading in the width and height, you read the height into the width. I think you just forgot to edit after copy.pasting it.

Fixing that will probably display the image again, and again wrong. What I am seeing in your screenshot, is once an image without transparent pixels normally displayed, and below that the image alpha blended, with some weird effects. In case you drew the image only once, I would like to know what the original picture looks like, and its height.

Quote:

---

Code:

---

                fseek(FileHandle, 12, SEEK_SET); // skip the basic file header data but read from the info header
                BMPInfo->biSize = 40; // the size of the struct, always 40 in my case (due to true color being used)
                fread(&ValuesBase, 1, 2, FileHandle);
                BMPInfo->biWidth = (long)ValuesBase[0]+(long)ValuesBase[1]*256; // only two bytes are read for TGAs
                fread(&ValuesBase, 1, 2, FileHandle);
                BMPInfo->biWidth = (long)ValuesBase[0]+(long)ValuesBase[1]*256; // only two bytes are read for TGAs

---

---

What do you think of this:

Code:

---

fseek(FileHandle, 12, SEEK_SET);
short width, height
fread(&width, 1, 2, FileHandle);
fread(&height, 1, 2, FileHandle);
BMPInfo->biWidth = (long)width;
BMPInfo->biHeight = (long)height;

---

Also, I don't understand where the hell your image is coming from! I don't see the code that turns MountainsData into a HBITMAP, and this:

Quote:

---

Code:

---

AlphaBlend(HDCBack, Mountains.XMain, Mountains.YMain, MountainsInfo.biWidth, MountainsInfo.biHeight, HDCScreen, 0, 0, MountainsInfo.biWidth, MountainsInfo.biHeight, AlphaUsage);

---

---

doesn't do anything useful. It draws from your window to your back buffer, and that has nothing to do with the image you want to AlphaBlend.

I mentioned of having fixed the double width mistake and it was indeed from using some copy paste (a special kind of paste that copies things). If you've seen the code in my massive reply above (#19), you'd see that I've got everything being drawn again and again, once per frame. The image simply doesn't appear or display. And no, I don't have run-length encoding (RLE) used with the image, it's uncompressed. At the bottom of my long message (#19), there are 3 links. One contains the TGA I'm trying to load (as a ZIP file - unzip it first then view it). The second URL is what I'm seeing. The third URL is what I should be seeing if successful.

http://www.ulillillia.us/temporary/MountainsBG.zip
http://www.ulillillia.us/temporary/CProgNoAlpha02.png
http://www.ulillillia.us/temporary/CProgNoAlpha03.png

From the best I can tell, it seems to be something with the structure, but having done a Google search, I'm supposedly using it correctly which leaves nothing else as problematic. Could it be Visual C++ 2005 Express being faulty or posing a limit? Am I using the wrong function? I don't see any other reason why it wouldn't work.

Quote:

---

Also, I don't understand where the hell your image is coming from! I don't see the code that turns MountainsData into a HBITMAP, and this:

Code:

---

AlphaBlend(HDCBack, Mountains.XMain, Mountains.YMain, MountainsInfo.biWidth, MountainsInfo.biHeight, HDCScreen, 0, 0, MountainsInfo.biWidth, MountainsInfo.biHeight, AlphaUsage);

---

doesn't do anything useful. It draws from your window to your back buffer, and that has nothing to do with the image you want to AlphaBlend.

---

The documentation didn't mention anything about an HBITMAP for either the blend function or the AlphaBlend function. It asks for two HDC's, four positions and four dimensions along with the blend function. Can you clarify what I need to do? Why two HDC's? Where would the HBITMAP go? In replacement of HDCScreen I take it?

In my last post I said that I don't see any code that displays your image, only a useless line that uses AlphaBlend to blend some pixels from the window to your screen buffer, so it's obvious that you aren't seeing the image. Maybe you could take a closer look at the TGA2_32::draw function I posted earlier.
Also let me say that you provide good information. But where did you buy that "copy paste". I'd like to copy my cat.

OK, that's the part you are missing. Let's say, GDI functions don't work with pointers to pixel data but with HBITMAPs. Actually, BitBlt work with two DCs. The first one is the DC you draw on (your back buffer), and the second one is a HDC associated with the HBITMAP, to get the data from. You blit from a DC, to a DC. That's very important.

Let's say you have the pixel data and the bitmap infoheader ready. This is a fragment from my code that creates a HBITMAP object:

(see next post)

You need a BITMAPINFO object, which contains a BITMAPINFOHEADER, and you already have a BITMAPINFOHEADER (MountainsInfo).

Code:

---

BITMAPINFO bmi = { MountainsInfo, };

// CreateDIBitmap() needs a device context handle, just like CreateCompatibleBitmap(), to
// ensure the created bitmap is compatible with the screen
HBITMAP hMountainsBitmap = CreateDIBitmap(HDCScreen, &bmi.bmiHeader, CBM_INIT, MountainsData, &bmi, DIB_RGB_COLORS);

//You need to keep this bitmap. When drawing it, you create a memory device context to blit
//from and associate it with hMountainsBitmap:

    HDC hMemDC = CreateCompatibleDC(HDCScreen);
    SelectObject(hMemDC, hMountainsBitmap);
    BLENDFUNCTION bf;
    bf.AlphaFormat = AC_SRC_ALPHA;
    bf.BlendOp = AC_SRC_OVER;
    bf.SourceConstantAlpha = 255;  // whatever you want
    bf.BlendFlags = 0;
    AlphaBlend(HDCBack, Mountains.XMain, Mountains.YMain, MountainsInfo.biWidth, MountainsInfo.biHeight, hMemDC, 0, 0, MountainsInfo.biWidth, MountainsInfo.biHeight, bf);
    DeleteDC(hMemDC);

---

That's it. Afterwards ypu should delete the HBITMAP object:

Code:

---

DeleteObject(hMountainsBitmap);

---

Looking at the BITMAPINFO structure, I see the info header thing and bmiColors. The "bmiColors" thing is confusing me. What do I put in there, if anything? The documentation says it should be either RGBQuad or something involving a palette. I don't use palettes (32-bit color, no palettes with that, just raw 0 to 255 values). Seeing the description of RGBQuad, it seems as if it would turn all pixels the same color. If I put 255 in for everything except the reserved one, wouldn't that make the image all white or would it retain the original brightness (where, if I used 85, it'd be a third as bright instead)? This is what's confusing me at the moment. I've set up the HBITMAP and a third DC. I've adjusted the AlphaBlend function to using this third DC (HDCBack being the first specified (the destination), and HDCBitmap for the second specified (the source).

Well, if you want to know, DIB_RGB_COLORS indicates that no palette is used so the palette in BITMAPINFO is ignored.

Okay, I've tested it and stuff and AlphaBlend is failing (nothing draws this time with AlphaBlend). From GetLastError, I see that there's an invalid parameter somewhere, the likely cause to it failing. Oh boy, here we go again:

Code:

---

BLENDFUNCTION AlphaUsage;
HDC HDCBitmap; // DC for bitmaps

unsigned char MountainsData[524288]; // The mountains background
LPVOID MountainsDataPointer;
BITMAPINFO MountainsMainInfo;
BITMAPINFOHEADER MountainsInfo;
LPBITMAPINFOHEADER MountainsInfoPointer;
HBITMAP MountainsBMPHandle;
struct SceneryData Mountains;

void InitializeDrawing()
{
        HDCScreen = GetDC(hwnd); // set the screen buffer DC
        HDCBack = CreateCompatibleDC(HDCScreen); // create a compatible DC, of which is to be used for drawing into the back buffer
        HDCBitmap = CreateCompatibleDC(HDCScreen); // for AlphaBlend
        MountainsMainInfo.bmiHeader = MountainsInfo;
        MountainsBMPHandle = CreateDIBitmap(HDCScreen, &MountainsMainInfo.bmiHeader, CBM_INIT, MountainsData, &MountainsMainInfo, DIB_RGB_COLORS);
        SelectObject(HDCBitmap, MountainsBMPHandle); // select the created bitmap
        HBMPBack = CreateCompatibleBitmap(HDCScreen, 800, 600); // create compatible bitmap, used for drawing into, but not on screen
        SelectObject(HDCBack, HBMPBack); // select the created bitmap
        ImageHandle = DrawDibOpen(); // set the DrawDib DC handle
        AlphaUsage.BlendOp = AC_SRC_OVER;
        AlphaUsage.BlendFlags = 0;
        AlphaUsage.SourceConstantAlpha = 255;
        AlphaUsage.AlphaFormat = AC_SRC_ALPHA;

... // front and back buffer things

        if (DebugTest[0] == 0)
        {
                DebugTest[0] = 1; // so this test is processed only once
                DebugTest[1] = HDCBitmap; // nonzero
                DebugTest[2] = MountainsBMPHandle; // nonzero
               
                sprintf(DebugDetails, "The resulting values are:\n%d\n%d\n%d\n%d\n%d.", DebugTest[1], DebugTest[2], DebugTest[3], DebugTest[4], DebugTest[5]); // for debugging
                MessageBox(hwnd, DebugDetails, "Debug Results", MB_OK);
        }
}

void DrawScenery()
{
        DrawDibDraw(ImageHandle, HDCBack, 0, 0, SkyBGInfo.biWidth, SkyBGInfo.biHeight, SkyBGInfoPointer, SkyBGDataPointer, 0, 0, SkyBGInfo.biWidth, SkyBGInfo.biHeight, 0);
        DrawDibDraw(ImageHandle, HDCBack, 0, 240, FogInfo.biWidth, FogInfo.biHeight, FogInfoPointer, FogDataPointer, 0, 0, FogInfo.biWidth, FogInfo.biHeight, 0);
        // DrawDibDraw(ImageHandle, HDCBack, Mountains.XMain, Mountains.YMain, MountainsInfo.biWidth, MountainsInfo.biHeight, MountainsInfoPointer, MountainsDataPointer, 0, 0, MountainsInfo.biWidth, MountainsInfo.biHeight, 0);
        // BitBlt(HDCBack, Mountains.XMain, Mountains.YMain, MountainsInfo.biWidth, MountainsInfo.biHeight, HDCScreen, MountainsInfo.biWidth, MountainsInfo.biHeight, SRCCOPY);
        // AlphaBlend(HDCBack, Mountains.XMain, Mountains.YMain, MountainsInfo.biWidth, MountainsInfo.biHeight, HDCScreen, 0, 0, MountainsInfo.biWidth, MountainsInfo.biHeight, AlphaUsage);
        DebugTest[3] = AlphaBlend(HDCBack, Mountains.XMain, Mountains.YMain, MountainsInfo.biWidth, MountainsInfo.biHeight, HDCBitmap, 0, 0, MountainsInfo.biWidth, MountainsInfo.biHeight, AlphaUsage);
       
        // AlphaBlend(HDCBack, 4, 112, 1024, 128, HDCScreen, 0, 0, 1024, 128, AlphaUsage);
       
        DrawDibDraw(ImageHandle, HDCBack, Logo.XMain, Logo.YMain, LogoInfo.biWidth, LogoInfo.biHeight, LogoInfoPointer, LogoDataPointer, 0, 0, LogoInfo.biWidth, LogoInfo.biHeight, 0);
        DrawDibDraw(ImageHandle, HDCBack, 640, 0, RightSidePanelInfo.biWidth, RightSidePanelInfo.biHeight, RightSidePanelInfoPointer, RightSidePanelDataPointer, 0, 0, RightSidePanelInfo.biWidth, RightSidePanelInfo.biHeight, 0);
        DrawDibDraw(ImageHandle, HDCBack, 0, 480, BottomSidePanelInfo.biWidth, BottomSidePanelInfo.biHeight, BottomSidePanelInfoPointer, BottomSidePanelDataPointer, 0, 0, BottomSidePanelInfo.biWidth, BottomSidePanelInfo.biHeight, 0);
       
        BitBlt(HDCScreen, 0, 0, WindowSizeBase.x, WindowSizeBase.y, HDCBack, 0, 0, SRCCOPY); // swaps the back and front buffers for displaying
       
        /*
        if (DebugTest[0] == 0)
        {
                DebugTest[0] = 1; // so this test is processed only once
                DebugTest[5] = GetLastError(); // shows 87 as the error code
               
                sprintf(DebugDetails, "The resulting values are:\n%d\n%d\n%d\n%d\n%d.", DebugTest[1], DebugTest[2], DebugTest[3], DebugTest[4], DebugTest[5]); // for debugging
                MessageBox(hwnd, DebugDetails, "Debug Results", MB_OK);
        }
        */
}

---

This is all that changed, and their relative positions. For the debug test things, test 1 and test 2 both show a nonzero value. Test 3 shows 0 indicating failure. Test 4 is unused and test 5 shows 87. What parameter is invalid?

I don't see any obvious error here. Are you sure you initialized MountainsMainInfo?
Also you can maybe check if the returned HBITMAP is not NULL.

Edit: you already checked for a valid bitmap handle I see. Only thing I can think of now is that you forgot to initialize the BITMAPINFO.

The only thing uninitialized with Bitmapinfo is the same thing that bothered me before and you told me it was fine like that - bmiColors. What do I put there? It seems as if I must use RGBQuad, but what do I use for it? Will it change all the pixels to white if I used 255's? I want the image to be displayed as is (outside adjusting it for fog only (intensity and color), of which I already know how to do this - I've done it since 2003).

This is what I did, which makes the unused values zero (instead of uninitialized):

Code:

---

        BITMAPINFO bmi =
        {
            {
                sizeof (BITMAPINFOHEADER),
                this->nWidth, bTopDown ? -this->nHeight : this->nHeight,
                1, 32,
            }
        };   
        this->hBmp = CreateDIBitmap(hCompDC, &bmi.bmiHeader, CBM_INIT, pPixelData,
                                    &bmi, DIB_RGB_COLORS);

---

(that bTopDown just has to do with supporting both top-down and bottom-up TGA files)

Seeing your original code, it's pretty logical that you saw the same image twice, because you copy an area from your window and blend it to the back buffer.

I'll stop now, tomorrow I'll probably be back.

I always use bottom-up TGA files. It matches BMPs and it helps keep consistency. Adding RGBQUAD causes the compiler to error saying:

c:\my documents\my programs\interactive animation\interactive animation\interactive animation.c(497) : error C2440: '=' : cannot convert from 'RGBQUAD' to 'RGBQUAD [1]'

Why am I getting this? The documentation doesn't have the [1] at the end....

The [1] doesn't mean that it's only one RGBQUAD, it's a trick to store an array of colors with variable length. It's meant to allocate it like this:
BITMAPINFO* pBmi = (BITMAPINFO*) malloc(sizeof (BITMAPINFOHEADER) + n * sizeof (RGBQUAD));
Then, you can access the colors [0] to [n-1].
But again, you don't need this because you are using 32 bits colors.

Now that you have created a bitmap object and made sure it is valid (I hope you have), maybe you could first try a simple BitBlt to draw the image without transparency?
If BitBlt also fails, there's something wrong with the bitmap or the memory DC.

And could you show me the code that initializes the BITMAPINFO in the WinMain function?

Well, basically, here's the code that I have for this:

Code:

---

BLENDFUNCTION AlphaUsage;
HDC HDCBitmap; // DC for bitmaps
RGBQUAD RGBColors;

unsigned char MountainsData[524288]; // The mountains background
LPVOID MountainsDataPointer;
BITMAPINFO MountainsMainInfo;
BITMAPINFOHEADER MountainsInfo;
LPBITMAPINFOHEADER MountainsInfoPointer;
HBITMAP MountainsBMPHandle;
struct SceneryData Mountains;

// in the "InitializeDrawing" function
        HDCScreen = GetDC(hwnd); // set the screen buffer DC
        HDCBack = CreateCompatibleDC(HDCScreen); // create a compatible DC, of which is to be used for drawing into the back buffer
        HBMPBack = CreateCompatibleBitmap(HDCScreen, 800, 600); // create compatible bitmap, used for drawing into, but not on screen
        SelectObject(HDCBack, HBMPBack); // select the created bitmap
        ImageHandle = DrawDibOpen(); // set the DrawDib DC handle
        AlphaUsage.BlendOp = AC_SRC_OVER;
        AlphaUsage.BlendFlags = 0;
        AlphaUsage.SourceConstantAlpha = 255;
        AlphaUsage.AlphaFormat = AC_SRC_ALPHA;
        RGBColors->rgbBlue = 255;
        RGBColors->rgbGreen = 255;
        RGBColors->rgbRed = 255;
        RGBColors->rgbReserved = 0;
        HDCBitmap = CreateCompatibleDC(HDCScreen); // for AlphaBlend
        MountainsMainInfo.bmiHeader = MountainsInfo;
        MountainsMainInfo.bmiColors = RGBColors;
        MountainsBMPHandle = CreateDIBitmap(HDCScreen, &MountainsMainInfo.bmiHeader, CBM_INIT, MountainsData, &MountainsMainInfo, DIB_RGB_COLORS);
        SelectObject(HDCBitmap, MountainsBMPHandle); // select the created bitmap

---

The InitializeDrawing function is called within the WinMain function, just before the main loop. The RGBQUAD element is causing the compiler to error.

Quote:

---

Originally Posted by ulillillia

I always use bottom-up TGA files. It matches BMPs and it helps keep consistency.

---

You can use a top-down bitmap in Windows, you just have to set the height to a negative value to make it happen.

Of course I know that, but some functions, like alpha blend, will not work when height is negative. The main thing is that it matches BMP files which otherwise helps keep the consistancy in style and retain maximum support. If I want bottom-up coordinates instead of top down (as most graphics edittors use), just take the image height, then subtract the coordinate and 1 extra. The coordinate (0, 255) on a 256x256 image is the bottom left pixel. 256 minus 255 gives 1 but the actual position is 0. It's simple math at about the 4th grade level.

Quote:

---

Originally Posted by ulillillia

Of course I know that, but some functions, like alpha blend, will not work when height is negative. The main thing is that it matches BMP files which otherwise helps keep the consistancy in style and retain maximum support. If I want bottom-up coordinates instead of top down (as most graphics edittors use), just take the image height, then subtract the coordinate and 1 extra. The coordinate (0, 255) on a 256x256 image is the bottom left pixel. 256 minus 255 gives 1 but the actual position is 0. It's simple math at about the 4th grade level.

---

Um, I know that. Didn't know that some functions couldn't work with top-down bitmaps. Sounds like those functions are badly broken.

As I explained you don't need to specify a color table of 1 entry (not that useful), so you don't need RGBQUAD.

Looking again at your Massive Reply, it seems you call InitializeDrawing before loading the targa file. So you try to create a bitmap with no bitmap data and an uninitialized BITMAPINFOHEADER.
(Note that when you create a HBITMAP, the pixel data your pointer points to is copied, so you can't use your own pointer to change the data later on.)
Am I right?

If I don't include RGBQuad, then AlphaBlend fails because the bitmapinfo thing has something uninitialized. If I do include it, then I just get compiler errors (cannot convert along with some others). You're saying I don't need it, but there's an uninitialized value if I don't include it. Please explain what I need to do.... You're only giving conflicting information.

Quote:

---

Originally Posted by ulillillia

If I don't include RGBQuad, then AlphaBlend fails because the bitmapinfo thing has something uninitialized.

---

So initialize it. Set it to NULL. The documentation clearly says this.

Quote:

---

Originally Posted by ulillillia

Of course I know that, but some functions, like alpha blend, will not work when height is negative.

---

Not if you try to mirror it vertically while drawing, by passing a negative height. But you can mirror it while creating a bitmap. For example, you can pass a negative height to CreateDIBitmap() to specify that the bitmap is top-down. That works fine.

Hey maybe you could just read my post and tell if I found the bug?

I'm not giving conflicting information. I explained what the RGBQUAD[1] is for, and then I told you that you don't need it. In post #36 I gave you an example from my code, in which I implicitly set the RGBQUAD stuff to 0.

Yes, it's working now and I calculated the resulting color displayed (after snagging a screenshot) and it is exactly what I'm expecting it to be. I ran my alpha transparency formula with the original on the background and the colors were off by fractions and rounding them gives identical values. I wonder what the premultiplication is used for and why it's needed.... Maybe for simplification of the formula (as, looking at my formula there, it's a little lengthy).

Yes, it was the placement of InitializeDrawing that messed things up. I moved it by using copy paste then commented out the original and it then worked. Yay! Now let's see if I can do the hills correctly which also has alpha. The bitmap font will be more complex since it gets cropped out with random amounts (for each character). I know how to get the character and location needed, cropping the image would be new. I'll try figuring that out on my own but if I'm unable to resolve it for some reason, then I'll ask about it again. Thanks for the assistance.

Yeah, finally, victory!! Pretty simple solution, actually:D.

I also noticed I misplaced the "initialize object positions" function. The two merely needed to be switched around. I've added the fog (and had a bug since I forgot to declare a char as unsigned then I had a copy paste mistake where I forgot to fix the array. The mountain's scaling is 1125 (exactly 10 miles distance) and the visibility is 1350 (exactly 12 miles). The fog now works exactly as expected. Yep, I've got the formula for fog as well, another derivative of the fundamental color-averaging formula. Next up, the hills (of which have a scaling of 900 (exactly 8 miles).

Great, it does not look hard at all to understand, your fog thing, if I'd only know what those words mean.

What are you confused about with the fog? The formula? What the fog does? I'm figuring out text displaying which uses AlphaBlend. I'm only having trouble getting wordwrap working right (infinite loops - oy!). The text stuff is a more complex usage of AlphaBlend. Everything is now working outside the text.

I only meant that I wouldn't know what BC, PDIST or VIS are.

BC - base color (the color without fog)
FG - fog color (the color of the fog at maximum intensity)
DIST - the object's distance (the more distance, the stronger the effect the fog has)
VIS - visibility (the distance at which fog has it's maximum effect).
MCOL - the resulting color, of which is displayed.

This screenshot shows the fog in my program. The visibility is 1350. The mountains have a scaling of 1125 making them 5/6 that of the fog color. The hills up closer have a scaling of 900 making them 2/3 that of the fog color. The houses have 3 making them almost unaffected by fog.

Edit: left out the MCOL variable

Ok thanks for that information, maybe I could use that some day.:cool: