Interesting problem with bmp drawing

This is a discussion on Interesting problem with bmp drawing within the C++ Programming forums, part of the General Programming Boards category; HI! I've been programming my bmp loader recently but got stuck in drawing this bmp... Everything is right for sqare ...

  1. #1
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    May 2004
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    Interesting problem with bmp drawing

    HI!
    I've been programming my bmp loader recently but got stuck in drawing this bmp... Everything is right for sqare bitmaps or bitmaps with height < width.
    But when bitmap height > than it's width the function draws it in a wrong way... Here's the code:

    Code:
    #include "stdio.h"
    #include "stdlib.h"
    #include "SDL.h"
    #include "bmp_load.h"
    
    //open file
    BMP::BMP(char *filename, SDL_Surface *scr)
    {
            FILE *f = fopen(filename, "rb");
            if(!f)
            {
                    printf("Couldn't open file %s\n", filename);
                    exit(1);
            }
    
            fread(&bF, sizeof(BITMAPFILEHEADER), 1, f);
            fread(&bI, sizeof(BITMAPINFOHEADER), 1, f);
    
            if(bF.bfType != BITMAP_ID)      //it's not a bitmap file
            {
                    printf("Wrong file! %s\n", filename);
                    exit(1);
            }
    
            fseek(f, bF.bfOffBits, SEEK_SET);
    
            imgData = (unsigned char*)malloc(bF.bfSize);
            fread(imgData, bF.bfSize, 1, f);
    
            screen = scr;
    
            isT = 0;
            fclose(f);
    }
    
    BMP::BMP()
    {
    
    }
    
    BMP::~BMP()
    {
            delete imgData;
    }
    
    int BMP::load(char *filename, SDL_Surface *scr)
    {
            FILE *f = fopen(filename, "rb");
            if(!f)
            {
                    printf("Couldn't open file %s\n", filename);
                    return 0;
            }
    
            fread(&bF, sizeof(BITMAPFILEHEADER), 1, f);
            fread(&bI, sizeof(BITMAPINFOHEADER), 1, f);
    
            if(bF.bfType != BITMAP_ID)      //it's not a bitmap file
            {
                    printf("Wrong file! %s\n", filename);
                    return 0;
            }
    
            fseek(f, bF.bfOffBits, SEEK_SET);
    
            imgData = (unsigned char*)malloc(bF.bfSize);
            fread(imgData, bF.bfSize, 1, f);
    
            screen = scr;
    
    	printf("Width: %d Height: %d\n", bI.biWidth, bI.biHeight);
    	
            fclose(f);
            return 1;
    }
    
    inline void BMP::draw_px(int x, int y, int r, int g, int b)
    {
            color = SDL_MapRGB(screen->format, r, g, b);
            bufp = (int*)screen->pixels+y*screen->pitch/4+x;
            *bufp = color;
    }
    
    void BMP::draw(int posX, int posY)
    {
            if(!isT)
            {
                    posY += bI.biHeight;
                    for(int j = 0; j < bI.biHeight; j++)
                            for(int i = 0; i < bI.biWidth; i++)
                                    draw_px(posX+i, posY-j, imgData[j*bI.biWidth*3+i*3+2], imgData[j*bI.biWidth*3 + i*3+1], imgData[j*bI.biWidth*3 + i*3]);
            } else { 
                    posY += bI.biHeight;
                    for(int j = 0; j < bI.biHeight; j++)
                            for(int i = 0; i < bI.biWidth; i++)
                                    if((imgData[j*bI.biWidth*3+i*3+2] != R) || (imgData[j*bI.biWidth*3+i*3+1] != G) || (imgData[j*bI.biWidth*3+i*3] != B))
                                            draw_px(posX+i, posY-j, imgData[j*bI.biWidth*3+i*3+2], imgData[j*bI.biWidth*3 + i*3+1], imgData[j*bI.biWidth*3 + i*3]);
            }
    
    
    }
    
    void BMP::setTransparent(int cR, int cG, int cB)
    {
            isT = 1;
            R = cR;
            G = cG;
            B = cB;
    }
    In my opinion the drawing function is wrong, but it could be also the loading function...
    Could you help me?

  2. #2
    Budding Synth Programmer samGwilliam's Avatar
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    The constructor and load () functions do pretty much the same thing. Why not have the constructor call load () and have the constructor-specific code (what little there is) just there?

    Not what you wanted to hear, but worth saying nontheless...
    MSVC++ 6.0

  3. #3
    Confused Magos's Avatar
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    Location
    Sweden
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    Did you take into account that if the width is not a multiple of 4 there are empty bytes at the end of each scanline?
    MagosX.com

    Give a man a fish and you feed him for a day.
    Teach a man to fish and you feed him for a lifetime.

  4. #4
    Registered User
    Join Date
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    Quote Originally Posted by Magos
    Did you take into account that if the width is not a multiple of 4 there are empty bytes at the end of each scanline?
    No, I didn't know it before :/
    Thanks!


    Hm... you're right... I don't know why I've rewritten that code twice instead of just calling load()
    (these are bad sides of programming at 2 a.m. :> )

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