Groups all (entity, meshRef) pairs by GfxObjId before drawing so each
GfxObj's sub-meshes are processed as a contiguous batch. Still uses
per-entity uniform uModel — visual output is identical to the old
StaticMeshRenderer — but the _groups dict is the structural prerequisite
for swapping to DrawElementsInstanced in the follow-up commit.
Key changes:
- New InstancedMeshRenderer.cs with CollectGroups() that fills
_groups[gfxObjId] = List<InstanceEntry> each frame, reusing the
inner List<> objects to avoid per-frame allocation.
- Same two-pass (opaque+clipmap first, translucent second) draw logic
from StaticMeshRenderer, now iterating over groups rather than raw
entity/meshRef pairs.
- GameWindow.cs: field and constructor swapped from StaticMeshRenderer
to InstancedMeshRenderer — public API is identical.
- 431 tests green, 0 warnings.
Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
