Function that will go through all texture object levels and count pixel counts and memory in bytes. Currently only Compressed textures formats are supported and RGB8 (RGB) or RGBA8 (RGBA)

CalcTexPixels.cpp

void CalculateTextureObjectPixels(GLuint texID, unsigned long *pixelCount, unsigned long *memoryUsed)
{
        int baseLevel = 0, maxLevel = 0;
        glGetTexParameteriv(GL_TEXTURE_2D, GL_TEXTURE_BASE_LEVEL, &baseLevel);
        glGetTexParameteriv(GL_TEXTURE_2D, GL_TEXTURE_MAX_LEVEL, &maxLevel);

        long pixels = 0, bytes = 0, bpp = 0;
        int texW = 0, texH = 0, texFmt = 0, compressed = 0, compressedBytes = 0;
        for (int level = baseLevel; level <= maxLevel; ++level)
        {
                glGetTexLevelParameteriv(GL_TEXTURE_2D, level, GL_TEXTURE_WIDTH, &texW);
                glGetTexLevelParameteriv(GL_TEXTURE_2D, level, GL_TEXTURE_HEIGHT, &texH);
                glGetTexLevelParameteriv(GL_TEXTURE_2D, level, GL_TEXTURE_INTERNAL_FORMAT, &texFmt);
                glGetTexLevelParameteriv(GL_TEXTURE_2D, level, GL_TEXTURE_COMPRESSED, &compressed);
                pixels += texW*texH;

                if (compressed == GL_TRUE)
                {
                        glGetTexLevelParameteriv(GL_TEXTURE_2D, level, GL_TEXTURE_COMPRESSED_IMAGE_SIZE, &compressedBytes);
                        bytes += compressedBytes;
                }
                else
                {
                        if (texFmt == GL_RGB || texFmt == GL_RGB8)
                                bpp = 3;
                        else if (texFmt == GL_RGBA || texFmt == GL_RGBA8)
                                bpp = 4;
                        else
                                bpp = 0;

                        bytes += texW*texH*bpp;
                }

                if (texW <= 1 && texH <= 1) // break when size is also 0
                        break;
        }
        *pixelCount += pixels;
        *memoryUsed += bytes;
}