Voxel Cone Tracing

Voxel Cone Tracing implementation

Latest screenshots

Indirect light

Ambient occlusion

Testing

Unit tests

To run the tests, do cargo test -- --test-threads 1. Because all tests initialize an OpenGL context, that gets cleaned up at the end of the test, they can't run concurrently.

Visual tests

Screenshots are stored in the root screenshots directory. The --visual-tests flag runs the program headless and draws the output to a framebuffer. This framebuffer is then compared to the stored screenshot with the name of the preset that was used. This means the following command will compare the output to the file screenshots/cornell-box-diffuse.png:

cargo run -- --scene cornell-box --preset cornell-box-diffuse --visual-tests

In the case you actually want to override the screenshot, you should also add the --update-screenshots flag:

cargo run -- --scene cornell-box --preset cornell-box-diffuse --visual-tests --update-screenshots

This flag also works when you want to create a screenshot of a new preset that doesn't have one yet.

Process

We voxelize the entire scene. This generates a voxel fragment list. We then use this list to create the sparse voxel octree (SVO). Every voxel fragment ends up in an octree leaf.

Every node has at least one child node unless it's the last level. This means there are no leaves on higher levels.

Standards

Octree terminology and utils

We'll use as an example the triangle.obj model.

This is node 0, it represents the whole scene -> [0, 0, 0, 0, 1, 2, 3, 4]. We find these nodes in the OCTREE_NODE_POOL buffer texture (could be called OCTREE_NODE_CHILD_POINTERS for consistency). Every one of the 8 elements in the node is a pointer to a child node.

If a texture holds pointers, its layout is r32ui, if it holds coordinates, it's rgb10_a2ui.

Level 0 is composed of node 0. Level 1 is composed of nodes 1, 2, 3, and 4. This is because the octree is sparse. The indices of the first nodes in each level are stored in OCTREE_LEVEL_START_INDICES. In our example, its [0, 1, 5, 9, 22, 65, 216, 775] for 8 levels.

We find the position of each of these nodes in OCTREE_NODE_POSITIONS. This positions are used

Each node has a brick that's accessed by its index in OCTREE_NODE_POOL_BRICK_POINTERS.

Each node's neighbor is stored in the buffer textures called OCTREE_NODE_POOL_NEIGHBOR_N, with N being one of (X, X_NEGATIVE, Y, Y_NEGATIVE, Z, Z_NEGATIVE).

_octreeTraversal.glsl holds functions to query the SVO with coordinates and get different results back. All of them return the node where they found the query coordinates, or NODE_NOT_FOUND if they did not.

How to debug compute shaders ("print debugging")

Create and bind a buffer texture

let (debug_texture, debug_texture_buffer) = helpers::generate_texture_buffer(size, gl::R32F, default_value);
helpers::bind_image_texture(image_index, debug_texture, gl::WRITE_ONLY, gl::R32F);

R32F is a good format since everything can be turned into a float.

Access texture in shader

uniform layout(binding = image_index, r32f) imageBuffer debugBuffer;

...

imageStore(debugBuffer, 0, vec4(float(someValue), 0, 0, 0));

Get values from buffer

let values = helpers::get_values_from_texture_buffer(debug_texture_buffer, size, default_value);
dbg!(&values);