Win Api Basics...

This is a discussion on Win Api Basics... within the Windows Programming forums, part of the Platform Specific Boards category; >i think the above posts explain it pretty well... >hDC = GetDC(hwnd); I tried all that. I also searched for ...

  1. #16
    Code Monkey Davros's Avatar
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    >i think the above posts explain it pretty well...
    >hDC = GetDC(hwnd);

    I tried all that.

    I also searched for example code written by other people, but nothing worked. What I ever I did, it would fail one in 20 times or so.

    I do read the manuals. Whatever was wrong with my code, it was something subtle that I couldn't figure out.
    OS: Windows XP
    Compilers: MinGW (Code::Blocks), BCB 5

    BigAngryDog.com

  2. #17
    * Death to Visual Basic * Devil Panther's Avatar
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    what do you mean it would fail one in 20 times?

    does it compile?
    "I don't suffer from insanity but enjoy every minute of it" - Edgar Allen Poe

    http://www.Bloodware.net - Developing free software for the community.

  3. #18
    Code Monkey Davros's Avatar
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    >does it compile?

    Of course. And it ran. And it worked - 1 in 20 times. But when it failed, GetDIBits would return invalid colour values in around half the image.

    I tried other's people code which was doing exactly the same thing I was, and that had the same problem. I have no issues with stability on my machine (i.e. no graphic card problems).

    Withouta really proper understanding of what was going on, and how the API was being used (which I have been unable to get from MSDN), I was unable to find a solution.

    In the end, I resolved my problem by calling a third party API, which I guess just wrapped GetDIBits, but it worked. So it must have been something wrong with what I was doing.

    Here was my code. Although I got my application to work now, I would still be interested to know what I did wrong.

    Code:
    int Gfx::create(Gfx& dst, void* src, int y, int cnt)
    {
      // (this code DOES NOT seem to work reliably)
      // Creates gfx data and fills it with contents of bitmap from
      // platform specific bitmap object src. At the moment, this method
      // only works under windows. Does nothing under any other platform.
      // If this method fails, rslt.data is NULL(0) & returns
      // platform specific error code. Error is -1 if operation
      // is not supported on platform.
      int err;
      if (y < 0) y = 0;
    
      // Ensure existing is destroyed.
      destroy(dst);
    
    #ifdef AIDAWIN
      // WINDOWS IMPLEMENTATION
      // src must not be 'selected into a device'
      err = 0;
      HDC hdc = 0;
      BITMAPINFO bmi;
      memset(&bmi, 0, sizeof(BITMAPINFO));
      bmi.bmiHeader.biSize = sizeof(BITMAPINFOHEADER);
    
      try
      {
        // Make temporary compatible device
        hdc = GetDC(0); // CreateCompatibleDC
        GdiFlush();
    
        // Get dimensions first
        GetDIBits(hdc, (HBITMAP)src, 0, 0, 0, &bmi, DIB_RGB_COLORS);
    
        // We always want positive height (bottom up bmp)
        bmi.bmiHeader.biHeight = abs(bmi.bmiHeader.biHeight);
    
        // Work out full size count if needed
        if (cnt <= 0) cnt = bmi.bmiHeader.biHeight - y;
    
        // Fill data
        dst.pDim.x = bmi.bmiHeader.biWidth;
        dst.pDim.y = cnt;
    
        // Check we can handle range
        err = ERROR_INVALID_PARAMETER;
    
        if (y + cnt <= bmi.bmiHeader.biHeight && cnt > 0)
        {
          // Set pixel format to be retrieved
          bmi.bmiHeader.biBitCount = 24;
          bmi.bmiHeader.biCompression = BI_RGB;
    
    ** HERE sz includes packing bytes
          int sz = dst.rowsz() * dst.pDim.y;
    
          if (sz > 0)
          {
            // Create memory array
            dst.pData = new char[sz];
    
    ** HERE  GetDiBits
            err = 0;
            if (GetDIBits(hdc, src, y, cnt, dst.pData,
              &bmi, DIB_RGB_COLORS) == 0)
            {
              // Error - destroy memory and
              // error code will be set below
              destroy(dst);
    ShowMessage("Y " + IntToStr(y));
    ShowMessage("CNT : " +IntToStr(cnt));
    
            throw Exception("Error " + IntToStr(GetLastError()));
            }
          }
        }
    
        // If no data - set error code
        if (dst.pData == 0)
        {
          dst.pDim = Axy();
          if (err == 0) err = GetLastError();
        }
    
        // Free temporary device context
        ReleaseDC(0, hdc);
      }
      catch(...)
      {
        // Clean-up
        destroy(dst);
        ReleaseDC(hdc);
        throw;
      }
    #else
      // NOT SUPPORTED
      err = -1;
    #endif
    
      return err;
    }
    OS: Windows XP
    Compilers: MinGW (Code::Blocks), BCB 5

    BigAngryDog.com

  4. #19
    Carnivore ('-'v) Hunter2's Avatar
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    Davros: I can't explain your problem, and I have no intention of reading through your code since I don't remember what parameters do what, and have no desire to read the documentations again But I did use GetDIBits once when I was trying to generate rotated bitmaps for my GDI graphics library, and never had any problems with it; if you care, you can sift through this and see if anything helps:
    Code:
    HBITMAP GFX::getRotatedBmp(HBITMAP orig, double angle, int rPointX, int rPointY)
    {
    	if(orig == NULL)
    		return NULL;
    
    	HBITMAP img;
    	HDC dcSrc = CreateCompatibleDC(dcFront);
    
    	RECT bounds = getBmpDimensions(orig);
    	int width = bounds.right + 1;
    	int height = bounds.bottom + 1;
    
    	img = CreateCompatibleBitmap(dcFront, width, height);
    
    	BITMAPINFO bi = {0};
    
    	bi.bmiHeader.biSize = sizeof(bi.bmiHeader);
    	bi.bmiHeader.biWidth = width;
    	bi.bmiHeader.biHeight = height;
    	bi.bmiHeader.biPlanes = 1;
    	bi.bmiHeader.biBitCount = 32;
    	bi.bmiHeader.biCompression = BI_RGB;
    
    	unsigned char* srcBits = new unsigned char[4 * width * height];
    	if(!GetDIBits(dcSrc, orig, 0, height, srcBits, &bi, DIB_RGB_COLORS))
    	{
    		delete[] srcBits;
    		return NULL;
    	}
    	unsigned char* destBits = new unsigned char[4 * width * height];
    
    	float sine = (float)sin(angle), cosine = (float)cos(angle); //Store result to save time
    	float cX = (float)rPointX, cY = (float)(bounds.bottom - rPointY); //Typecast & convert from normal coords
    	float tempX, tempY; //Offset on source to centre the image
    
    	tempX = (cX*(cosine-1) - cY*sine);
    	tempY = (cY*(cosine-1) + cX*sine);
    
    	int origX, origY;
    
    	unsigned char* destLine = destBits;
    	for(int y = 0; y < height; ++y)
    	{
    		for(int x = 0; x < width; ++x)
    		{
    			origX = (int)(((float)x + tempX)*cosine + ((float)y + tempY)*sine);
    			origY = (int)(((float)y + tempY)*cosine - ((float)x + tempX)*sine);
    
    			if(origX >= 0 && origY >= 0 && origX < bounds.right && origY < bounds.bottom)
    			{
    				destLine[(x << 2)    ] = srcBits[((origX + width*origY) << 2)    ];
    				destLine[(x << 2) + 1] = srcBits[((origX + width*origY) << 2) + 1];
    				destLine[(x << 2) + 2] = srcBits[((origX + width*origY) << 2) + 2];
    			}
    			else
    			{
    				destLine[(x << 2)    ] = 0;
    				destLine[(x << 2) + 1] = 0;
    				destLine[(x << 2) + 2] = 0;
    			}
    		}
    		destLine += (width << 2);
    	}
    
    	SetDIBits(dcSrc, img, 0, height, destBits, &bi, DIB_RGB_COLORS);
    
    	DeleteDC(dcSrc);
    
    	delete[] srcBits;
    	delete[] destBits;
    
    	return img;
    }
    Just Google It. √

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  5. #20
    Code Monkey Davros's Avatar
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    >I have no intention of reading through your code

    I can understand that. I did try simplifying my code in a previous post, but found I made so many typo errors in the simplification, that it made the effort pointless.

    >if you care, you can sift through this and see if anything helps

    Thanks. I will do so.

    Cheers for the reply.
    OS: Windows XP
    Compilers: MinGW (Code::Blocks), BCB 5

    BigAngryDog.com

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