Methods
_computeScissor()
Compute the projector frustum screen-space AABB in pixels (origin = bottom-left). Returns:
- true + filled
_scissorrect when the projector is on-screen. - false when the projector is entirely off-screen (caller should skip the draw).
If any frustum corner is behind the main camera (w<=0), falls back to the full viewport (CPU-side near-plane clipping of the volume is too costly to be worth it here).
apply()
Apply per-projector additive projector color(lighting) into the currently bound framebuffer.