[Unity] Star Glow

This is an example show that how to use post-processing to create the star glow effect.

ApplyBrightnessEffect(src, brightness);
ApplyBlurEffect(brightness, blur1, blur2, composite);
CompositeEffect(src, dst, composite);

The overall idea could be summarized as the following steps:

1. Extract bright regions that are above a certain threshold
2. Apply blur effect along the star streak direction
3. Combine all the blur images together as a composite image
   Blend OneMinusDstColor One
4. Combine the composite image with the original image

The blurred image along is computed as :

for (int j = 0; j < 4; j++) {
  color += saturate(tex2D(_MainTex, uv) * pow(_BlurAttenuation,   
  i.power * j));
  uv += i.offset;
}

where we define the offset as :

var glowAngle = anglePerDivision * i + glowAngleOffset;
var blurOffset = (Quaternion.AngleAxis(glowAngle, Vector3.forward) * Vector2.up).normalized;
offset = _MainTex_TexelSize.xy * _BlurOffset * o.power;