Module dda_sprite 

Clean-room KV6 sprite raycaster for the DDA backend (Substage DDA.8).

Renders KV6 sprites by per-pixel ray casting: for every screen pixel the sprite covers, transform the camera ray into the sprite’s local voxel space, 3D-DDA through the KV6, and depth-composite the first solid voxel against the shared z-buffer. Clean-room (no voxlap code), the sprite counterpart to the terrain renderer in crate::dda.

Depth parity. Transforming the ray by the inverse sprite basis leaves the ray parameter unchanged in world units — a hit at local parameter t is at world point cam.pos + dir·t — so the perpendicular depth is t · (dir·forward), exactly the convention crate::dda writes for terrain. Sprites therefore occlude and are occluded by DDA terrain correctly.

Shading reads the KV6 voxel’s baked brightness byte (high byte of the packed colour) via [crate::dda::shade] — the clean-room brightness model, not voxlap’s dir-LUT reflection shading.

Functions

draw_sprite_dda

Draw one KV6 Sprite into (fb, zb) by per-pixel ray casting, depth-compositing against whatever the terrain pass already wrote. Returns the number of pixels written.