有没有更快的方法在 OpenGL 中指定立方体贴图纹理？

Question

I'm specifying cubemap texture for my skybox in the following way:

 glTexImage2D(GL_TEXTURE_CUBE_MAP_POSITIVE_X + 0, 0, GL_RGB, width, height, 0, GL_RGB, GL_UNSIGNED_BYTE, texData(0));
 glTexImage2D(GL_TEXTURE_CUBE_MAP_POSITIVE_X + 1, 0, GL_RGB, width, height, 0, GL_RGB, GL_UNSIGNED_BYTE, texData(1));
 glTexImage2D(GL_TEXTURE_CUBE_MAP_POSITIVE_X + 2, 0, GL_RGB, width, height, 0, GL_RGB, GL_UNSIGNED_BYTE, texData(2));
 glTexImage2D(GL_TEXTURE_CUBE_MAP_POSITIVE_X + 3, 0, GL_RGB, width, height, 0, GL_RGB, GL_UNSIGNED_BYTE, texData(3));
 glTexImage2D(GL_TEXTURE_CUBE_MAP_POSITIVE_X + 4, 0, GL_RGB, width, height, 0, GL_RGB, GL_UNSIGNED_BYTE, texData(4));
 glTexImage2D(GL_TEXTURE_CUBE_MAP_POSITIVE_X + 5, 0, GL_RGB, width, height, 0, GL_RGB, GL_UNSIGNED_BYTE, texData(5));

texData is an unsigned char* vector .

Using Visual Studio Debugger I found that each line takes about 4ms to run, so using 6 lines to specify the cubemap texture takes about 20-25ms in total. I update this cubemap texture in each iteration of my main loop, and it is slowing down my main loop considerably. I know skyboxes are tradionally static but my application needs the skybox to be updated because I'm creating a 360 video viewer.

Is there another way to specify the cubemap texture that could be faster? I have checked OpenGL's docs already but I don't see a faster way.

UPDATE: I replaced glTexImage2D with glTexSubImage2D for all iterations except the 0th iteration and now the total time taken by 6 glTexSubImage2D lines is under 5ms. This is satisfactory for me but I guess I'll leave the question open because technically there's no answer yet.

Answer 1

glTexImage is slower as every time you call it, it will allocate memory on driver side and copy pixel data from your image from CPU to GPU, which happens over the bus.

On the other hand, glTexSubImage is not allocating memory every time. On first call it allocates memory and holds the pointer to it. Later it just copies directly to the memory via that pointer.

I think depending on filtering flags you mention, OpenGL might be creating different texture levels.

Try using glTexStorage2D with level 1 .

Also, try using SOIL library - it has one function with simple API to load cubemap.

One other thing you can try is compressing textures and then profile your program - I am sure this option should give you the best performance.

Answer 2

glTexImage2D is slow because it is copying large amounts of dqta from CPU memory to GPU memory. If the images are coming from a video decoder, they are possibly already in GPU memory. In such a case you might be able to texturize then using OpenGL extensions.

These tend to be platform specific though.