Add uUseTexture==2 (RGBA modulate) branch to ui_text.frag so dat sprites
can be drawn through the existing 2D batcher without touching the font path.
TextRenderer gains _spriteBufs (per-GL-handle List<float>), DrawSprite(), and
a Flush block that issues one draw call per distinct texture with uUseTexture=2.
Also adds DepthMask(false) in the state-save block (restored to true after) to
prevent the transparent-quad pass from writing depth and corrupting the 3D scene
if the UI is flushed mid-frame.
TextureCache gains GetOrUpload(surfaceId, out width, out height) — caches pixel
dimensions alongside the GL handle so UI 9-slice geometry can compute slice UVs
from the source image size without a second decode.
UiRenderContext gains a DrawSprite forwarder that applies the current 2D
translate stack, matching the DrawRect / DrawRectOutline pattern.
Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
c9eef1d7cd