message: Restrict channel to rgb
diff: @@ -11,7 +11,7 @@ declare abstract class AbstractBaseMaskFilter extends PIXI.Filter {
  * The fragment shader which renders this filter.
  * A subclass of AbstractBaseMaskFilter must implement the fragmentShader(channel) static field.
  */
  - static fragmentShader: ((channel: string) => string) | null;
  + static fragmentShader: ((channel: 'r' | 'g' | 'b') => string) | null;
  /**
  * A factory method for creating the filter using its defined default values
  @@ -22,7 +22,7 @@ declare abstract class AbstractBaseMaskFilter extends PIXI.Filter {
  */
  static create(
  defaultUniforms?: ConstructorParameters<typeof PIXI.Filter>[2],
  - channel?: string
  + channel?: 'r' | 'g' | 'b'
  ): AbstractBaseMaskFilter;
  /**
  