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# OpenGL Voxel Cone Tracing Experiment - Progress

## 28 posts in this topic

As for what I meant by anti-aliasing, I realized I'm not sure what I meant. Or rather I'm not sure how you'd go about implementing it. With voxelization in the way everyone does it you're always implementing solid voxel blocks. Somewhere in my head there's this idea of implementing blocks with an alpha value to cover cases where a mesh is partly in a voxel's space but not enough to register in solid. As in, when the Buddha model is moving back and forth instead of it's voxelization popping from 0 to 1 in a binary fashion from voxel space to voxel space, there'd be a smooth transition, filling in an alpha value of that voxel space as more of the mesh takes it up.

I figured out how to do voxel "anti-aliasing" by getting the vertex position (transformed to inverse voxel space - each voxel is one unit) of each dominant axis and subtracting the integer version of that value, during the voxelization stage in the geometry shader. i.e. if a vertex's dominant axis is x and its x position is 32.4 (out of 64x64x64 maximum position), then it is 0.4 filled of voxel 32. I transfer this value into the fragment shader as a density value and multiply it by the final alpha value.

The problem is, it doesn't seem to help at all, in some cases, making it worse.

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As for what I meant by anti-aliasing, I realized I'm not sure what I meant. Or rather I'm not sure how you'd go about implementing it. With voxelization in the way everyone does it you're always implementing solid voxel blocks. Somewhere in my head there's this idea of implementing blocks with an alpha value to cover cases where a mesh is partly in a voxel's space but not enough to register in solid. As in, when the Buddha model is moving back and forth instead of it's voxelization popping from 0 to 1 in a binary fashion from voxel space to voxel space, there'd be a smooth transition, filling in an alpha value of that voxel space as more of the mesh takes it up.

I figured out how to do voxel "anti-aliasing" by getting the vertex position (transformed to inverse voxel space - each voxel is one unit) of each dominant axis and subtracting the integer version of that value, during the voxelization stage in the geometry shader. i.e. if a vertex's dominant axis is x and its x position is 32.4 (out of 64x64x64 maximum position), then it is 0.4 filled of voxel 32. I transfer this value into the fragment shader as a density value and multiply it by the final alpha value.

The problem is, it doesn't seem to help at all, in some cases, making it worse.

What's making it worse? I just visualized the alpha filling in, but as I've said I've not done it myself, nor have I seen anyone else even suggesting it. Any videos to show what's going on?

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What's making it worse? I just visualized the alpha filling in, but as I've said I've not done it myself, nor have I seen anyone else even suggesting it. Any videos to show what's going on?

I guess I've stated my assumption in the wrong manner. What I have meant to say was that the way I was implementing it was making the flickering worse. Something to do with the way I accumulate my lighting. I envision that by having a one voxel offset from the surface may provide what I want. Anyhow, lately I haven't had time to think about this and I have decided to put this on hold until a later stage.

In the meanwhile, I am trying to get better filtering for my voxels.

Original 2x2x2 bricks:

[attachment=15278:giboxemunfilt.jpg]

[attachment=15279:giboxemfilt.jpg]

no noticeable performance loss at all.

However, for optimal filtering, I'm going to need to use octrees instead of directly using 3D textures because 3D textures do not allow me to sample at offsets of less than 1 texel.

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Here's an update after some tweaking of some parameters (increasing diffuse cone trace to 1.0 from 0.3 and adjusting bounce attenuation). I've also turned off the ugly cone traced shadows - I need to work out a better way of getting shadows:

[attachment=16355:giboxv2-0.png][attachment=16356:giboxv2-1.png]

[attachment=16357:giboxv2-2.png][attachment=16358:giboxv2-3.png]

[attachment=16359:giboxv2-4.png][attachment=16360:giboxv2-5.png]

As you can see, the diffuse is a lot more realistic and consistent - especially with emissive object lighting.

The last image demonstrates multiple bounces with emissive lighting.

Now I'm hoping to work out a way of getting accurate soft-shadows that also occur with emissive object lighting. It seems the fastest way would be to assign all emissive objects as lights and switch to deferred rendering for deferred shadow mapping. The darkness of the shadowing would be a function of the emissivity parameter. But with point-light sources, I would need some sort of dual-paraboloid shadow mapping, which would be slow.

I wonder if there is another way such as ray-tracing shadows. I've already seen the artifacts of cone-tracing shadows, which are very apparent with the sphere - they show up very voxelized (unless someone has an idea of how to filter these better during sampling).

The biggest limitation of cone tracing shadows is that I have to trace a cone in the direction of every light - meaning that performance is highly dependent on the number of light sources I have in the scene.

I was thinking another way would be to implement some sort of ambient occlusion, which is similar to tracing a shadow cone, but instead of tracing one in the direction of every light source, I would just have a set number of multiple cones that capture averaged visibility.

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