OpenGL Video RAM Limits

Question

I have been trying to make a Cross-platform 2D Online Game, and my maps are made of tiles. My tileset, which I render the tiles from, is quite huge. I wanted to know how can I disable hardware rendering, or at least making it more capable. Hence, I wanted to know what are the basic limits of the video ram, as far as I know, Direct3D has a texture size limits (by that I don't mean the power-of-two texture sizes).

Answer 1

If you want to use a software renderer, link against Mesa.

You can get an estimate of the maximum texture size using these methods:

21.130 What's the maximum size texture map my device will render hardware accelerated?

A good OpenGL implementation will render with hardware acceleration whenever possible. However, the implementation is free to not render hardware accelerated. OpenGL doesn't provide a mechanism to ensure that an application is using hardware acceleration, nor to query that it's using hardware acceleration. With this information in mind, the following may still be useful:

You can obtain an estimate of the maximum texture size your implementation supports with the following call:

GLint texSize;
glGetIntegerv(GL_MAX_TEXTURE_SIZE, &texSize);

If your texture isn't hardware accelerated, but still within the size restrictions returned by GL_MAX_TEXTURE_SIZE, it should still render correctly.

This is only an estimate, because the glGet*() function doesn't know what format, internalformat, type, and other parameters you'll be using for any given texture. OpenGL 1.1 and greater solves this problem by allowing texture proxy.

Here's an example of using texture proxy:

glTexImage2D(GL_PROXY_TEXTURE_2D, level, internalFormat, width, height, border, format, type, NULL);

Note the pixels parameter is NULL, because OpenGL doesn't load texel data when the target parameter is GL_PROXY_TEXTURE_2D. Instead, OpenGL merely considers whether it can accommodate a texture of the specified size and description. If the specified texture can't be accommodated, the width and height texture values will be set to zero. After making a texture proxy call, you'll want to query these values as follows:

GLint width;
glGetTexLevelParameteriv(GL_PROXY_TEXTURE_2D, 0, GL_TEXTURE_WIDTH, &width);

if (width==0) {
   /* Can't use that texture */
}