Loading a TGA File and Using it with OpenGL

Question

I currently am trying to load a tag file with c++ and rendering it with OpenGL. Currently the colors are all mixed up (red becomes blue, green becomes red, and blue becomes green). My current code for putting it into the video memory is.

glTexImage2D(GL_TEXTURE_2D, 0, GL_RGB, width, height, 0, GL_RGB, GL_UNSIGNED_BYTE, data);

Where the data is the pixel data and the rest is self explanatory. The files are saved with no compression are in 24 bits saved from photoshop.

Post a complete, minimal program that demonstrates the problem. — genpfault, Aug 12 '11 at 21:07
@Jjack:Perhaps you could post a picture of what you're getting? — Nicol Bolas, Aug 12 '11 at 23:52
Change to: glTextImage2D(GL_TEXTURE_2D, 0,GL_RGB , widht, height, 0, GL_BRG, GL_UNSIGNED_BYTE, data); It just because you read TGA that have other order of colors (or you read them in wrong order). That you should change second GL_RBG to GL_BRG. For more see here: http://www.opengl.org/sdk/docs/man/xhtml/glTexImage2D.xml — przemo_li, Aug 13 '11 at 15:06

score 6 · Answer 1 · edited Oct 13 '15 at 19:45

Your glTexImage2D is correct, so that's not the problem.

I do need (when loading TGA files) to swap the color components. Try this:

typedef struct
{
    unsigned char imageTypeCode;
    short int imageWidth;
    short int imageHeight;
    unsigned char bitCount;
    unsigned char *imageData;
} TGAFILE;

bool LoadTGAFile(char *filename, TGAFILE *tgaFile)
{
    FILE *filePtr;
    unsigned char ucharBad;
    short int sintBad;
    long imageSize;
    int colorMode;
    unsigned char colorSwap;

    // Open the TGA file.
    filePtr = fopen(filename, "rb");
    if (filePtr == NULL)
    {
        return false;
    }

    // Read the two first bytes we don't need.
    fread(&ucharBad, sizeof(unsigned char), 1, filePtr);
    fread(&ucharBad, sizeof(unsigned char), 1, filePtr);

    // Which type of image gets stored in imageTypeCode.
    fread(&tgaFile->imageTypeCode, sizeof(unsigned char), 1, filePtr);

    // For our purposes, the type code should be 2 (uncompressed RGB image)
    // or 3 (uncompressed black-and-white images).
    if (tgaFile->imageTypeCode != 2 && tgaFile->imageTypeCode != 3)
    {
        fclose(filePtr);
        return false;
    }

    // Read 13 bytes of data we don't need.
    fread(&sintBad, sizeof(short int), 1, filePtr);
    fread(&sintBad, sizeof(short int), 1, filePtr);
    fread(&ucharBad, sizeof(unsigned char), 1, filePtr);
    fread(&sintBad, sizeof(short int), 1, filePtr);
    fread(&sintBad, sizeof(short int), 1, filePtr);

    // Read the image's width and height.
    fread(&tgaFile->imageWidth, sizeof(short int), 1, filePtr);
    fread(&tgaFile->imageHeight, sizeof(short int), 1, filePtr);

    // Read the bit depth.
    fread(&tgaFile->bitCount, sizeof(unsigned char), 1, filePtr);

    // Read one byte of data we don't need.
    fread(&ucharBad, sizeof(unsigned char), 1, filePtr);

    // Color mode -> 3 = BGR, 4 = BGRA.
    colorMode = tgaFile->bitCount / 8;
    imageSize = tgaFile->imageWidth * tgaFile->imageHeight * colorMode;

    // Allocate memory for the image data.
    tgaFile->imageData = (unsigned char*)malloc(sizeof(unsigned char)*imageSize);

    // Read the image data.
    fread(tgaFile->imageData, sizeof(unsigned char), imageSize, filePtr);

    // Change from BGR to RGB so OpenGL can read the image data.
    for (int imageIdx = 0; imageIdx < imageSize; imageIdx += colorMode)
    {
        colorSwap = tgaFile->imageData[imageIdx];
        tgaFile->imageData[imageIdx] = tgaFile->imageData[imageIdx + 2];
        tgaFile->imageData[imageIdx + 2] = colorSwap;
    }

    fclose(filePtr);
    return true;
}

Please correct the comment 'Read 13 bytes' to 'Read 9 bytes' like int the code — Maciej Szpakowski, Jun 16 '16 at 23:22

score 0 · Answer 2 · edited Nov 05 '13 at 21:48

0

glTexImage2D(GL_TEXTURE_2D, 0, GL_RGBA, Width,Height, 0,
         GL_BGRA_EXT, GL_UNSIGNED_BYTE, Pixels);

TRY This I had The Same Problem Every thing was blue it had the texture pattern just not the color

edited Nov 05 '13 at 21:48

Benjamin Toueg

10,511
7
48
79

answered Nov 05 '13 at 21:29

Mastereus

1

Loading a TGA File and Using it with OpenGL

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