nx_raster_legacy.nx

nx_raster.nx -- software 2D rasterizer (lines + triangles). Closes the GRAPHICS-PATH gap named in docs/VULKAN_COMPARISON.md. Vulkan / OpenGL / DirectX / Metal all do graphics; we had zero rasterizer until this brick. Pure i64 substrate -- no FPU, no GPU dependency -- runs on every backend including Cortex-M3 with a framebuffer. L2 canonical primitive composing: nx_image.Image (L1 canonical pixel container) nx_loop.LoopVerdict (bounded loops) ===== Algorithms ================================================ Lines: Bresenham 1965 (the canonical integer-only rasterizer). Pure integer ops; no division beyond /2 and bit shifts. O(max(dx, dy)) pixels visited. Triangles: edge-function method (Pineda 1988 "A Parallel Algorithm for Polygon Rasterization"). For each triangle vertex pair, compute the 2D cross product (the "edge function") at each pixel; pixel is inside the triangle iff all three edge functions have the same sign. Bounding-box prune to avoid testing the whole framebuffer. Barycentric: the three edge functions ARE the barycentric coordinates (after normalization by triangle area). Free interpolation of per-vertex attributes. ===== Why pure i64 ============================================== Substrate has no FPU yet (compiler I2 parked). All rasterization can be done in i64 with edge functions and barycentric weights scaled to Q10. Subpixel accuracy via fixed-point coordinate input (caller passes coords in Q4 or Q8 if needed; this v1 accepts i64 pixel-aligned coordinates). Subpixel coords + perspective-correct attribute interpolation queued for v2.