Shadow Mask

Shadow Mask (Shadow mask) is a technical term that is extremely important in rendering and optimizing game graphics (technical art). A middle-rendering technology that minimizes shadow calculations during runtime by burning the shadow information cast by static background objects onto dynamic objects (characters, etc.) into a dedicated texture (Shadowmask) that is separate from the lightmap.

Real-world analogy: Instead of re-measuring the (static) shadow of a huge building on a road at night with a spotlight every night, you can take the shortcut of ``drawing the outline of the shadow in black chalk (shadow mask)'' on the road in advance

Shadow mask is ``the ultimate cheat sheet technique in which the shadow cast by a huge stationary building (static shadow) is written down in advance on a special notebook (Shadowmask texture) on the ground and burned in.'' The moment the character (dynamic object) enters the noted area (chalked shadow), only the character's feet will automatically darken, and the shadows of the buildings in the background will be blended beautifully like real-time shadows. Since there is no need to rotate the shadow calculation camera every frame, the GPU load is dramatically reduced.

Detailed mechanism and operating principle

Set the lighting mode to "Shadowmask" and pre-bake. Only static shadow information is saved in an ultra-lightweight texture (Shadowmask) dedicated to shadows, and at runtime, shadows are synthesized simply by reading numerical values ​​from there.