​

varying vec2 vTexCoord;

uniform sampler2D uTexture0;

​

uniform vec2 uScale;

​

void main() {

​

  vec2 uv = vTexCoord;

  uv.y = 1.0 - uv.y;

  // Sample our texture

  vec4 color = texture2D(uTexture0, uv);

  // Convert to gray scale

  // color.rgb = vec3((color.r + color.g + color.b) / 3.0);

  // we will plug these into smoothstep

  // Colors less than edge will be black

  // Colors brighter than edge + feather will be white

  // Colors in between edge and edge plus feather will be grayscale

  float edge = uScale.x;

  float feather = uScale.y;

  // Smoothstep the colors

  // color.rgb = smoothstep(edge, edge + feather, color.rgb);

  // Smoothstep just red for a lighting effect

  color.r = smoothstep(edge, edge + feather, color.r);

  // You could also just do step instead

  // color.rgb = step(edge, color.rgb);

  // Send the color to the screen

  gl_FragColor = color;

​

}