Ambient lighting. Defer texture filtering

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+# Lighting
+
+## Forward
+
+```
+for each triangle:
+    for each pixel:
+        for each light:
+            shade(pixel, light)
+```
+
+- Overdraw penalty.
+- Client must specify all lights (for the object) up front.
+
+## Deferred
+
+### Forward Pass
+
+The forward pass generates:
+- Depth
+- Texture ID
+- Texture coordinates
+
+Sampling of textures is deferred to avoid overdraw penalty.
+
+### Pixel-centric Shading
+
+```
+for each pixel:
+    for each light:
+        shade(pixel, light)
+```
+
+- Need a pixel-in-volume test.
+- Inefficient if most pixels are not affected by a light.
+  - Ok:  ambient, directional.
+  - Bad: point, area.
+
+### Light-centric Shading
+
+```
+for each light:
+    volume <- project light volume
+    for each pixel in volume:
+        shade(pixel, light)
+```
+
+- Need to project the light volume.
+- Shades only the pixels that are covered by the volume.
+- For ambient and directional, the volume is all space.
+
+## Clustered
+
+### Cluster Generation
+
+```
+for each light:
+    volume <- project light volume to NDC
+    for each cluster:
+        test(cluster, volume)
+```
+
+- Need a volume-AABB test (the cluster is an AABB in NDC space.)
+- Lighting then proceeds as in deferred.