672d25b02d
Split shadow rendering per LOD per tilemap and improve fragment shader invocation rate by using multi-viewport. Also changes the layout of the atlas to be 4 x 4 x Layers. This allow to grow the atlas while keeping the content and page indirection correct, but this isn't implemented in this patch. # First attempt Shadow rendering using atomic proved to be less than ideal and performance were not quite to an acceptable level. The previous method had issue with atomic contention when a lot of triangle would overlap and too many fragment shader invocations with quite complex indirection rules and biases which made the technique costly. The new implementation leverage multi viewport and layered rendeing to effectively replace the need for atomic and render directly to the shadow atlas. Using the well supported extension these are free on modern hardware and do not need a geometry shader. One view per tile is needed since we use the viewport index and the layer index as a way to index a specific tile in the array. # Geometric Complexity Problem The counterpart of this is that we need to draw one geometry instance per tile which is 32x32 time more instances (at most) than with the previous method. This means that we will have to find a way to mitigate this geometry cost by either reducing the number of tiles per tilemaps (in other words, making the system less memory efficient) or splitting complex objects' geometry into smaller, more cull friendly chunks (for example, like the sculpt PBVH nodes). The later seems to be a longer term solution as it requires way too much engineering time we have right now. # Update Lag Problem This also mean we can only update up to 64 tile per redraw which is not enough even in the most basic cases. This leads to missing or over shadowing when a light updates until there is no updates and the shadow rendering can catch up. One possible solution is to update a lower LODs first waiting until there is no update to render. This would allow no artifact during the transforms (unless there is too many light updates even for lowest LOD, but that was an issue also for the previous implementation). This could also help with the geometric complexity. # Solution In the end, we decided to have one view per lod. This limits the complexity of the fragment shader (improve speed), reduces the number of views per tilemap (fix update lag), and reduces the number of instances. This also mean we cannot render directly to the atlas anymore and reverted to the atomic solution. Using the smallest possible viewport, we assure that there isn't that much fragment shader invocations which was one of the bottleneck. And also reduces the amount of geometry instances that pass the clipping test. Pull Request: https://projects.blender.org/blender/blender/pulls/110979
Blender
Blender is the free and open source 3D creation suite. It supports the entirety of the 3D pipeline-modeling, rigging, animation, simulation, rendering, compositing, motion tracking and video editing.
Project Pages
Development
License
Blender as a whole is licensed under the GNU General Public License, Version 3. Individual files may have a different, but compatible license.
See blender.org/about/license for details.