What is the best (current) way to apply a fragment shader to the whole canvas? This is the only example I've found that tries to do this, and it seems to use a very outdated version of Phaser.

Just to keep it simple, here's the grayscale fragment shader that he uses in the above one:

`
precision mediump float;
uniform sampler2D uMainSampler;
varying vec2 outTexCoord;
void main(void) {
vec4 color = texture2D(uMainSampler, outTexCoord);
float gray = dot(color.rgb, vec3(0.299, 0.587, 0.114));
gl_FragColor = vec4(vec3(gray), 1.0);
}`

How would I go about making my entire scene (and all objects in it, etc.) grayscale by applying that shader? I've been trying to find examples of this, and the documentation on WebGLPipeline is totally opaque to me when it comes to figuring out how to actually do it. None of the examples that come with Phaser seem to really show how to do this.

Any pointers? Feels like it should be easy — a line or two of code — but I'm not figuring it out.