import type { VertexLayout } from '../context/vertex-layout';
import type { Shader } from '../context/shader';
import type { ExcaliburGraphicsContextWebGL } from '../context/excalibur-graphics-context-webgl';

/**
 * PostProcessors can be used to apply a shader to the entire screen. It is recommended
 * you use the {@apilink ScreenShader} to build your post processor shader.
 *
 * The screen texture comes through as this uniform
 *
 * `uniform sampler2D u_image`
 *
 * Post processor shaders get some default uniforms passed to them
 *
 * `uniform float u_time_ms` - total playback time in milliseconds
 * `uniform float u_elapsed_ms` - the elapsed time from the last frame in milliseconds
 * `uniform vec2 u_resolution` - the resolution of the canvas (in pixels)
 *
 * Custom uniforms can be updated in the {@apilink PostProcessor.onUpdate}
 */
export interface PostProcessor {
  initialize(graphicsContext: ExcaliburGraphicsContextWebGL): void;
  getShader(): Shader;
  getLayout(): VertexLayout;
  /**
   * Use the onUpdate hook to update any uniforms in the postprocessors shader
   *
   * The shader has already been bound so there is no need to call shader.use();
   * @param elapsed
   */
  onUpdate?(elapsed: number): void;

  /**
   * Use the onDraw hook to upload any textures or command that need to run right before draw
   * @param elapsed
   */
  onDraw?(): void;
}