dropoff of line as it thickens

modules/globebrowsing/shaders/asdf_fs.glsl

@@ -25,9 +25,15 @@
 #include "fragment.glsl"
 
 uniform vec3 color;
+uniform vec2 viewport;
+uniform float lineWidth;
+
+in vec2 center;
 
 Fragment getFragment() {
+  float dist = 1.0 - length(gl_FragCoord.xy - center) / lineWidth;
+  float alpha = pow(dist, 2.5);
   Fragment frag;
-  frag.color = vec4(color, 1);
+  frag.color = vec4(color, alpha);
   return frag;
 }

modules/globebrowsing/shaders/asdf_gs.glsl

@@ -30,12 +30,21 @@ layout (triangle_strip, max_vertices = 6) out;
 uniform vec2  viewport;
 uniform float lineWidth;
 
+out vec2 center;
+
 void main()
 {
   vec4 p0 = gl_in[0].gl_Position;
-  vec4 p1 = gl_in[1].gl_Position;
-  vec4 p2 = gl_in[2].gl_Position;
-  vec4 p3 = gl_in[3].gl_Position;
+  p0.xyz /= p0.w;
+
+  vec4 p1 = gl_in[1].gl_Position/gl_in[1].gl_Position.w;
+  p1.xyz /= p1.w;
+
+  vec4 p2 = gl_in[2].gl_Position/gl_in[2].gl_Position.w;
+  p2.xyz /= p2.w;
+
+  vec4 p3 = gl_in[3].gl_Position/gl_in[3].gl_Position.w;
+  p3.xyz /= p3.w;
 
   vec2 p = normalize((p1.xy - p0.xy) * viewport);
   vec2 pn = vec2(-p.y, p.x);
@@ -48,26 +57,32 @@ void main()
 
   // P2
   gl_Position = p1 + vec4(pn * lineWidth / viewport, 0, 0);
+  center = 0.5 * (1.0 + p1.xy) * viewport;
   EmitVertex();
 
   // V0
   gl_Position = p1 + vec4(ln * lineWidth / viewport, 0, 0);
+  center = 0.5 * (1.0 + p1.xy) * viewport;
   EmitVertex();
 
   // V1
   gl_Position = p1 - vec4(ln * lineWidth / viewport, 0, 0);
+  center = 0.5 * (1.0 + p1.xy) * viewport;
   EmitVertex();
 
   // V2
   gl_Position = p2 + vec4(ln * lineWidth / viewport, 0, 0);
+  center = 0.5 * (1.0 + p2.xy) * viewport;
   EmitVertex();
 
   // V3
   gl_Position = p2 - vec4(ln * lineWidth / viewport, 0, 0);
+  center = 0.5 * (1.0 + p2.xy) * viewport;
   EmitVertex();
 
   // N1
   gl_Position = p2 - vec4(nn * lineWidth / viewport, 0 , 0);
+  center = 0.5 * (1.0 + p2.xy) * viewport;
   EmitVertex();
 
   EndPrimitive();