add simple game-of-life demo

example/life.js

@@ -0,0 +1,76 @@
+const regl = require('../regl')()
+
+const RADIUS = 512
+const INITIAL_CONDITIONS = (Array(RADIUS * RADIUS * 4)).fill(0).map(
+  () => Math.random() > 0.9 ? 255 : 0)
+
+const state = (Array(2)).fill().map(() =>
+  regl.framebuffer({
+    colorBuffer: regl.texture({
+      radius: RADIUS,
+      data: INITIAL_CONDITIONS,
+      wrap: 'repeat'
+    }),
+    depth: false
+  }))
+
+const updateLife = regl({
+  frag: `
+  precision mediump float;
+  uniform sampler2D prevState;
+  varying vec2 uv;
+  void main() {
+    float n = 0.0;
+    for(int dx=-1; dx<=1; ++dx)
+    for(int dy=-1; dy<=1; ++dy) {
+      n += texture2D(prevState, uv+vec2(dx,dy)/float(${RADIUS})).r;
+    }
+    float s = texture2D(prevState, uv).r;
+    if(n > 3.0+s || n < 3.0) {
+      gl_FragColor = vec4(0,0,0,1);
+    } else {
+      gl_FragColor = vec4(1,1,1,1);
+    }
+  }`,
+
+  framebuffer: (args, id, params) => state[(params.count + 1) % 2]
+})
+
+const setupQuad = regl({
+  frag: `
+  precision mediump float;
+  uniform sampler2D prevState;
+  varying vec2 uv;
+  void main() {
+    float state = texture2D(prevState, uv).r;
+    gl_FragColor = vec4(vec3(state), 1);
+  }`,
+
+  vert: `
+  precision mediump float;
+  attribute vec2 position;
+  varying vec2 uv;
+  void main() {
+    uv = 0.5 * (position + 1.0);
+    gl_Position = vec4(position, 0, 1);
+  }`,
+
+  attributes: {
+    position: regl.buffer([ -4, -4, 4, -4, 0, 4 ])
+  },
+
+  uniforms: {
+    prevState: (args, id, params) => state[params.count % 2].color[0]
+  },
+
+  depth: { enable: false },
+
+  count: 3
+})
+
+regl.frame(() => {
+  setupQuad(() => {
+    regl.draw()
+    updateLife()
+  })
+})