c - 我们如何从 GLSL 中获取变量值？

Question

我正在做一个需要大量计算的项目，我有一个想法是将工作交给 GPU，但我想知道我们是否可以从 GLSL 检索结果，如果可能的话，如何？

Answer 1

除了放在帧缓冲区中的内容之外，GLSL 不提供输出。

要对 GPU 进行编程并更方便地获得结果，请使用CUDA（仅限 NVidia）或OpenCL（跨平台）。

Answer 2

In general, what you want to do is use OpenCL for general-purpose GPU tasks. However, if you are insistent about pretending that OpenGL is not a rendering API...

Framebuffer Objects make it relatively easy to render to multiple outputs. This of course means that you have to structure your processing such that what gets rendered matches what you want. You can render to 32-bit floating-point "images", so you have access to plenty of precision. The biggest difficulty is what I stated: figuring out how to structure your task to match rendering.

It's a bit easier when using transform feedback. This is the ability to write the output of the vertex (or geometry) shader processing to a buffer object. This still requires structuring your tasks into something like rendering, but it's easier because vertex shaders have a strict one-vertex-to-one-vertex mapping. For every input vertex, there is exactly one output. And if you draw GL_POINTS, it's not too difficult to use attributes to pass the data that changes.

Both easier and harder is the use of shader_image_load_store. This is effectively the ability to read/write from/to arbitrary images "whenever you want". I put that last part in quotes because there are lots of esoteric rules about data race conditions: reading from a value written by another shader invocation and so forth. These are not trivial to deal with. You can try to structure your code to avoid them, by not writing to the same image location in the same shader. But in many cases, if you could do that, you could just render to the framebuffer.

Ultimately, it's pretty much impossible to answer this question in the general case, without knowing what exactly you're trying to actually do. How you approach GPGPU through a rendering API depends greatly on exactly what you're trying to compute.