PIXI.MaskSystem

There are three built-in types of masking: Scissor Masking: Scissor masking discards pixels that are outside of a rectangle called the scissor box. It is the most performant as the scissor test is inexpensive. However, it can only be used when the mask is rectangular. Stencil Masking: Stencil masking discards pixels that don't overlap with the pixels rendered into the stencil buffer. It is the next fastest option as it does not require rendering into a separate framebuffer. However, it does cause the mask to be rendered twice for each masking operation; hence, minimize the rendering cost of your masks. Sprite Mask Filtering: Sprite mask filtering discards pixels based on the red channel of the sprite-mask's texture. (Generally, the masking texture is grayscale). Using advanced techniques, you might be able to embed this type of masking in a custom shader - and hence, bypassing the masking system fully for performance wins.

The best type of masking is auto-detected when you push one. To use scissor masking, you must pass in a Graphics object with just a rectangle drawn.

Mask Stacks

In the scene graph, masks can be applied recursively, i.e. a mask can be applied during a masking operation. The mask stack stores the currently applied masks in order. Each PIXI.BaseRenderTexture holds its own mask stack, i.e. when you switch render-textures, the old masks only applied when you switch back to rendering to the old render-target.