iPhone OpenGL ES Texture Pipeline for JPEG

Question

I am having trouble getting my texture pipeline working for JPEGs. Everything works right for PNGs but converting over has been an issue.

I am loading by image data via UIImage and CGBitmapContextCreate

UIImage* tI = [UIImage imageWithContentsOfFile:fileName];
Image = tI.CGImage;

mWidth = CGImageGetWidth(Image);
mHeight = CGImageGetHeight(Image);

mData = new uint8[mWidth * mHeight * 4];

Context = CGBitmapContextCreate(mData, mWidth, mHeight, CGImageGetBitsPerComponent(Image), CGImageGetBytesPerRow(Image), 
                                CGImageGetColorSpace(Image), 
                                CGImageGetBitmapInfo(Image));

CGContextDrawImage(Context, CGRectMake(0.0, 0.0, float(mWidth), float(mHeight)), Image);
CGContextRelease(Context);

Then I setup my GLTexture with the call...

glTexImage2D(GL_TEXTURE_2D, 0, GL_RGB, texture->Width(), texture->Height(), 0, GL_RGB, GL_UNSIGNED_BYTE, texture->Data());

I suspect this glTexImage2D call is the issue. I have been using different combinations to try and get things to work. The BitmapInfo state for alpha is 'kCGImageAlphaNoneSkipLast' so I am not sure if I should be using RGBA and GL_UNSIGNED_SHORT_5_5_5_1 but no combination I have tried worked so far. The closest I got was...

glTexImage2D(GL_TEXTURE_2D, 0, GL_RGBA, texture->Width(), texture->Height(), 0, GL_RGBA, GL_UNSIGNED_BYTE, texture->Data());

which gave me very blown out texture (color edges were discernable but everything was too bright)

Any help would be great. I am using JPEGs to try and save space over PNGs.

Answer 1

Your mData buffer is too big. JPEG images don't support alpha, so there are only three components per pixel (RGB), whereas you'd usually use four for PNGs (RGBA).