To generate more sophisticated lighting, with area shadows, sky occlusion, colored light bounces, etc, we’ll have to trace some rays. I found this article very funny, like an adventure, even though I didn’t know 1/3 of the terms, also learned something. Alpha channels also contain interesting things like world-space texel size and triangle ID. I do multiple iterations with low res, then with a final high res pass – known as ‘Final Gathering’, which is what the ‘brute force’ primary GI engine refers to. That’s why I had to also invent some mip-mapping tricks, so I don’t need crazy amount of memory to bake large worlds. However, there is another problem. We will start with picture on the left and will make it look like the one on the right: Contents: I consider it a success. You signed in with another tab or window. Originally intended for my own game, I decided to make it a product by itself and hopefully help other people bake nice lighting. Why should we even care about ray distance, what happens if it’s unlimited? Push texel center outside using both hit face normal and ray direction. Adjusting sample positions is a massive improvement: And another comparison, before and after: Next thing to address is the wrong self-shadowing of smooth low-poly surfaces. In some cases like using stratified sampling, the rays are naturally aligned, so sorting won’t be much useful. they're used to gather information about the pages you visit and how many clicks you need to accomplish a task. Very cool! Adding constant bias to ray start (used in many offline renderers), Making shadow rays ignore adjacent faces that are almost coplanar (used in 3dsmax in “Advanced Ray-Traced Shadow” mode), Tessellating/smoothing geometry before ray-tracing (mentioned somewhere), Blurring the result (mentioned somewhere), Trace a ray from flat position to smooth position, If there is an obstacle, use flat, otherwise smooth. Ray bias I agree, Enlighten’s mesh projection is a great idea. ( Log Out /  Just render the UV layout with, say, 8x MSAA, then resolve it without any blur by either using any sample or somehow averaging them. I’ll go over each of these problems one by one. There is an interesting preprocess step I didn’t describe in the article when I throw some rays from one lightmap to another and check texel size at the hit to determine which mip level would suffice for GI. In fact 0.0000002 is a rounded version of FLT_EPSILON. They have a lot of similarities, so knowing one should give you an idea of how to operate the other: you define surfaces, build an acceleration structure and intersect rays against it. Previously OptiX denoiser was only trained on non-HDR data (although input/output is float3). I am working on a GPU lightmapper now, I try to bake single lightmap for the highest LOD,and mapped it to other LODs. Attempting to push it behind more distant faces with leave the texel incorrectly shadowed. or are they done on the CPU side only? Hit me up if you are! Unfortunately I don’t have a working code of this implementation anymore, but I remember it was pretty bad. I expect more attention to this problem in the future, as real-time ray-tracing is getting bigger, and games can’t just apply real tessellation to everything like in offline rendering. Once again, there are multiple ways to fix it. Push positions outside of closed surfaces. This problem is fairly common in ray-tracing in general  and often mentioned as the “shadow terminator problem” (google it). It should at least have: Smooth position obtained by Phong Tessellation adapted to only produce convex surfaces. In accordance with the art. Brute force search can be terribly slow. Shadow leaks occur because texels are large. Draw a UV GBuffer using (pseudo) conservative rasterization. Take an edge and test its first vertex against first vertices of its neighbours: If so, perform same tests on second vertices, Now also check if edge UVs share a line segment. Simply using rounded “smooth” position gets us here: Almost nice But what is this little seam on the left? The windows are realistic in size, made according to an architect's plan. We use essential cookies to perform essential website functions, e.g. You can always update your selection by clicking Cookie Preferences at the bottom of the page. It is usually combined with explicit skylight cubemap sampling + ray clamping firefly rejection. Here I specifically mean sorting the rays so they have much coherent memory access behavior during BVH traversal thus much better traversal performance. The image above was the first time the lightmapper was tested on a relatively large map. They can create rays, trace them by executing and waiting for intersection/hit programs (also new shader types) and then obtain the result. The whole point of tracing the bitmask and dilating these spots inside is to minimize shadow leaking in mips, while not affecting the original texture. Render using this layout, or transfer texels from the original layout to this one after rendering. Right: multi-tap rasterization. When combined with typical smooth interpolated normals, it looks wrong. All of them had one thing in common – something had to be rasterized in UV space. Results are projected into SH basis and saved as a texture per coefficient. I also wanted to mention that the quality of the lightmap is exceptional, it's really smooth and there are no splotches or smudges anywhere. To overcome this you need to balance the amount of sunlight with skylight and possibly interior lighting. Quite often (e.g. Lightmass importance volume is put in place. Unlike path tracing, since all the materials are diffuse, we can sort the lightmap texels rather than rays and still get ‘sorted’ performance. To avoid aforementioned MSAA problems, we can have a centered sample with zero offset, always rendered last on top of everything else (or you can use depth/stencil buffer and render it first instead… but I was lazy to do so, and it’s not a perf-critical code). Even given some imperfections, I think the quality is quite good for most cases and simple to understand/implement comparing to least squares.

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