Software renderer redesign for 0.15.0

[afritz1]

The existing software renderer is a naive 2.5D ray caster and retains several poor design choices from the past few years. Although it has a couple optimizations like multi-threading and per-pixel-column occlusion culling, it was meant only for prototyping new features. I am rewriting it for 0.15.0 so it is actually decent (more importantly: optimizable) and can match Arena's appearance more closely with 8-bit palette colors instead of true color.

Part 1

• Scrap 2.5D ray caster, salvaging important functions
• Implement scene graph which feeds the renderer geometry and lights and keeps gameplay details (voxels/entities/sky/etc.) away. The renderer stores only frame buffers and allocated textures; it does not own geometry
• Implement 3D triangle rasterization (projection, clipping, barycentric coordinates, debug RGB colors, perspective correctness)
• Implement all pixel shaders using 8-bit textures and light tables, supporting material types (i.e. opaque/alpha-tested/ghost)
• Don't need optimization or features like dithering or multi-threading in bulk yet
• Some color/palette bugs are okay

Part 2

• Prepare for 0.15.0 release, fix bugs
• All features in to look identical to Arena (i.e. dithering)
• More scene graph optimizations (antiportal occlusion culling, multi-threading)
• See how close to 2160p 60 fps we can get

Branch naming convention: sw-renderer-redesign-part-#

[afritz1]

Revised roadmap as of 1/13/2024.

Part 1

• [x] Implement 3D triangle rasterization (projection, clipping, barycentric coordinates, perspective correctness)
• [x] Implement vertex buffers, attribute buffers, and index buffers
• [x] Implement 8-bit texturing
• [x] Implement basic scene graph which feeds the renderer draw calls every frame for visible geometry
• [x] Implement one pixel shader for all geometry just to get everything on-screen
• [x] Various engine design clean-ups to support renderer development as needed (scene management, etc.)
• [x] Get to a geometry-complete state with the chunk system, meaning all voxels and entities are appearing in-world

Part 2

• [x] Get to a geometry-complete state with sky objects, particles, and screen-space fog (fog shading not required)
• [x] Implement pixel shader per material (opaque, alpha-tested, ghost, chasm wall, etc.)
• [x] Implement sky gradient using dither textures
• [x] Implement lights using light tables and basic forward rendering, supporting up to 8 lights per draw call
• [x] Get to a complete state with lighting voxels and entities using the light levels from the original game
• [x] Get appearance to be nearly identical to Arena while supporting any screen resolution

Part 3

• [x] Implement voxel visibility manager using quadtree
• [x] Optimize voxel draw call generation
• [x] Implement entity visibility manager using bounding boxes
• [x] Optimize entity draw call generation
• [x] Implement sky object visibility manager
• [x] Optimize sky object draw call generation
• [x] Change triangle clipping from world space to clip space
• [x] Implement lighting using clip space -> world space transform in rasterizer
• [x] Render sky and weather near the camera and without depth testing so far plane can be closer
• [x] Sort entities by distance (fixes ghost rendering)
• [x] Prioritize lights by distance (fixes shading with tightly-grouped lights)
• [x] Implement puddle shader again
• [x] Optimize rasterizer and pixel shading for higher pixels per second
• [x] Add multi-threaded pixel shading

[afritz1]

#252 is a big enough issue with rain/snow that it should be considered a blocker for finishing part 3.

[afritz1]

Done with #252.

[afritz1]

Going to skip harder optimizations like occlusion culling and just optimize the rasterizer and shaders a more conventional way with fewer special cases/algorithms/etc..

Ideally opaque meshes would draw front to back without depth reads and then sky would draw after it with a depth < INFINITY check, but that's too hard to implement, so instead going to draw sky first and then everything else after it.

[afritz1]

Deciding how to handle tiled rendering with puddles and ghosts, because these two shaders have to read from the frame buffer. I think trying to do multi-pass shading is a good idea instead of coming up with a complex tile scheduler to keep threads from blocking on unfinished tiles.

[afritz1]

Added multi-threading today but performance is still poor even with very high threads. I think the binning design will need to change so they store much more work for each thread, instead of needing threads to synchronize every 8 or so draw calls.