Graphics › Light
Direct and indirect light
Know first: Normals and light, Surface properties: roughness, metallic, AO, How an engine draws a frame: passes and the G-buffer
Light reaches every point of a scene by two routes: straight from a source, and bounced off everything around it. The second route is why shadows are not black, and why a room is bright even where the sun never shines. This lesson goes through the kinds of light source and why a lamp twice as far away gives only a quarter of the light. It also explains why the sun is thousands of times brighter than a room, and how engines calculate bounced light. It is the sixth lesson of the course “How an engine draws a frame.”
Why this matters
In the lesson “Normals and light,” a face grew brighter as it turned toward the sun, and a face turned away went black. In real life, shadows are almost never black. Without the second route, these things make no sense:
- why a shadow on a sunny day looks bluish, and why you can see every corner of a room by the window;
- why a lamp raised higher lights a table much worse, while the sun lights the ground and a rooftop equally well;
- why the same scene is black one moment and blown out the next, and what the camera’s “eye” is adjusting;
- what Lumen, baked light and probes are, and what they charge for their good looks.