Simple glow shader for HUD elements

Simple glow shader for HUD elements

Postby kodi » Sun Oct 06, 2019 1:42 am

This is a shader meant for hud graphics that are supposed to glow. The larger you want your glow to be, the more transparent space you'll need to have around the edge of your graphic.
The armor pieces on the little dude at the left edge of the screen shows the effect.

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//texture glow fragment shader by kodi
//use as you wish, no need to ask. Credits appreciated though!

//control the shader with these. Both radialSamples and size affect performance. The former should not be a lower value than the latter.
const int radialSamples = 16;
const int size = 8;
const float intensity = 0.005;

//full revolution in radians
const float twopi = 6.2831;

vec4 Process(vec4 color)
   vec2 tc = gl_TexCoord[0].st; //coordinate of the fragment(pixel) in the image
   vec4 color1 = getTexel(tc); //texture color of fragment
   ivec2 texSize = textureSize(tex, 0); //texture size in pixels
   vec2 pixel = 1.0/vec2(texSize); //pixel size in a normalized 0-1.0 range
   vec4 newcolor = color1;
   if(color1.a <= 0) //if the fragment is transparent we attempt adding glow
      for(int i=1; i<=radialSamples; i++) //in this loop, we rotate around the fragment to check color of neighbouring ones
         float angle = twopi*(float(i)/float(radialSamples)); //angle, increases each time "i" does.
         vec2 offset = vec2(cos(angle)*pixel.x,sin(angle)*pixel.y); //gets offset to a pixel adjacent to the original
         for(int j=1; j<=size; j++) //in this loop, we check the color of (size) amount of pixels in a straight line
            vec4 glowSample = getTexel(tc+(offset*float(j))); //gets the color of a new sample   
            newcolor.rgb = newcolor.rgb + (glowSample.rgb*intensity);  //adds to the original
            newcolor.a = min(1.0, newcolor.a+(glowSample.a*intensity)); //adjusts and caps alpha
   return newcolor;
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