What is the preferred way to show large images in OpenGL

Question

I\'ve had this problem a couple of times. Let\'s say I want to display a splash-screen or something in an OpenGL context (or DirectX for that matter, it\'s more of a conceptual

Answer 1

If this is a single frame splash image with no animations, then there's no harm using glDrawPixels. If performance is crucial and you are required to use a texture, then the correct way to do it is to determine at runtime, the maximum supported texture size, using a proxy texture.

GLint width = 0;
while ( 0 == width ) {  /* use a better condition to prevent possible endless loop */
    glTexImage2D(GL_PROXY_TEXTURE_2D, 
                      0,                /* mip map level */
                      GL_RGBA,          /* internal format */
                      desiredWidth,     /* width of image */
                      desiredHeight,    /* height of image */
                      0,                /* texture border */
                      GL_RGBA           /* pixel data format, */ 
                      GL_UNSIGNED_BYTE, /* pixel data type */
                      NULL              /* null pointer because this a proxy texture */
    );

    /* the queried width will NOT be 0, if the texture format is supported */
    glGetTexLevelParameteriv(GL_PROXY_TEXTURE_2D, 0, GL_TEXTURE_WIDTH, &width);

    desiredWidth /= 2; desiredHeight /= 2;
}

Once you know the maximum texture size supported by the system's OpenGL driver, you have at least two options if your image doesn't fit:

• Image tiling: use multiple quads after splitting your image into smaller supported chunks. Image tiling for something like a splash screen should not be too tricky. You can use glPixelStorei's GL_PACK_ROW_LENGTH parameter to load sections of a larger image into a texture.
• Image resizing: resize your image to fit the maximum supported texture size. There's even a GLU helper function to do this for you, gluScaleImage.

Answer 2

I don't think there is a built-in opengl function, but you might find a library (or write the function yourself) to break the image down into smaller chunks and then print to screen the smaller chunks (128x128 tiles or similar).

I had problem with this using Slick2D for a Java game. You can check out their "BigImage" class for ideas here.