CODEWITHSUNDEEP
c++openglglsl
xthexder
xthexder

Reputation: 1565

Transferring large voxel data to a GLSL shader

I'm working a program which renders a dynamic high resolution voxel landscape.

Currently I am storing the voxel data in 32x32x32 blocks with 4 bits each:

struct MapData {
    char data[32][32][16];
}

MapData *world = new MapData[(width >> 5) * (height >> 5) * (depth >> 5)];

What I'm trying to do with this, is send it to my vertex and fragment shaders for processing and rendering. There are several different methods I've seen to do this, but I have no idea which one will be best for this.

I started with a sampler1D format, but that results in floating point output between 0 and 1. I also had the hinting suspicion that it was storing it as 16 bits per voxel.

As for Uniform Buffer Objects I tried and failed to implement this.

My biggest concern with all of this is not having to send the whole map to the GPU every frame. I want to be able to load maps up to ~256MB (1024x2048x256 voxels) in size, so I need to be able to send it all once, and then resend only the blocks that were changed.

What is the best solution for this short of writing OpenCL to handle the video memory for me. If there's a better way to store my voxels that makes this easier, I'm open to other formats.

Upvotes: 3

Views: 3037

Answers (1)

Nicol Bolas
Nicol Bolas

Reputation: 473174

If you just want a large block of memory to access from in a shader, you can use a buffer texture. This obviously requires a semi-recent GL version (3.0 or better), so you need DX10 hardware or better.

The concept is pretty straightforward. You make a buffer object that stores your data. You create a buffer texture using the typical glGenTextures command, then glBindTexture it to the GL_TEXTURE_BUFFER target. Then you use glTexBuffer to associate your buffer object with the texture.

Now, you seem to want to use 4 bits per voxel. So your image format needs to be a single-channel, unsigned 8-bit integral format. Your glTexBuffer call should be something like this:

glTexBuffer(GL_TEXTURE_BUFFER, GL_RUI8, buffer);

where buffer is the buffer object that stores your voxel data.

Once this is done, you can change the contents of this buffer object using the usual mechanisms.

You bind the buffer texture for rendering just like any other texture.

You use a usamplerBuffer sampler type in your shader, because it's an unsigned integral buffer texture. You must use the texelFetch command to access data from it, which takes integer texture coordinates and ignores filtering. Which is of course exactly what you want.

Note that buffer textures do have size limits. However, the size limits are often some large percentage of video memory.

Upvotes: 7

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