[Purdze]

Type of change

• Bug fix
• New feature
• Breaking change
• Refactor / code cleanup
• Performance improvement
• Chore / tooling
• Documentation

Summary

shadows under moving mobs flickered. Position::lerp used glam's a * (1 - s) + b * s, which isn't exact when both ends match: an interpolation step at y = -60 gave -60.00000000000001, the shadow's floor dropped to the cell inside the block below, and the shadow vanished for that frame (about a third of frames while a mob moves on superflat). it now uses a + s * (b - a) like Mth.lerp, which covers interpolation steps and the per-frame render lerp.

Reference

Vec3.lerp, Mth.lerp, LinearInterpolationHandler.doInterpolate, EntityRenderer.extractShadow

Testing

unit test that a lerp between equal positions stays exact at -60 and -63; this is the reliable guard. new entities/shadow_interpolation nudges a pig by one wire step (1/4096 of a block) six times and matches ten frames of each interpolation against the still one, allowing 100 pixels for the nudge's edge flips (a lost shadow changes ~3700). whether a frame lands on the bad tick depends on tick timing the harness can't pin, so on master it failed 4 of 6 runs; with the fix it passes every run, and on the vanilla harness. adds max_differing_pixels to match_screenshots for that. full just ingame-test passes.

other position lerps (first-person camera pivot, particles, the dark-disc eye height) still use the inexact form; none feeds a block floor, so they're left for a separate change.