Refactor arc shader so it uses only matrix uniform

shader/twoD/arc.frag

@@ -1,34 +1,34 @@
 #version 430 core
 in vec4 gColor;
-in vec2 cenPosT;
 in float gRadIn;
-in float gRadOut;
 in vec2 angles;
+in vec2 dist;
 out vec4 fColor;
-out float gl_FragDepth;
 
-uniform float rotation;
+//uniform float rotation;
 
 void main()
 {
-  vec2 pos = gl_FragCoord.xy;
-  float d = distance(pos,cenPosT);
-  float dTest = max ( step(gRadOut/2,d)
-                    , 1 - step(gRadIn/2,d)
-                    );
-
-  vec2 posDiff = pos - cenPosT;
-  float sa = angles.x - rotation;
+//  vec2 pos = gl_FragCoord.xy;
+//  float d = distance(pos,cenPosT);
+//  float dTest = max ( step(gRadOut/2,d)
+//                    , 1 - step(gRadIn/2,d)
+//                    );
+//
+//  vec2 posDiff = pos - cenPosT;
+  float sa = angles.x;
   vec2 sv = vec2 (-sin(sa), cos(sa));
-  float saTest = dot(sv,posDiff) >= 0 ? 0 : 1;
-  float ea = angles.y - rotation;
+//  float saTest = dot(sv,posDiff) >= 0 ? 0 : 1;
+  float ea = angles.y;
   vec2 ev = vec2 (-sin(ea), cos(ea));
-  float eaTest = dot(ev,posDiff) <= 0 ? 0 : 1;
-  float aTest = ea - sa < radians(180) ? max (saTest,eaTest) 
-                                       : min (saTest,eaTest);
-
-  float onArcTest = max(dTest,aTest); 
-
-  gl_FragDepth = max(gl_FragCoord.z , onArcTest);
+//  float eaTest = dot(ev,posDiff) <= 0 ? 0 : 1;
+//  float aTest = ea - sa < radians(180) ? max (saTest,eaTest) 
+//                                       : min (saTest,eaTest);
+//
+//  float onArcTest = max(dTest,aTest); 
+//
+//  gl_FragDepth = max(gl_FragCoord.z , onArcTest);
+ float d = (dist.x * dist.x) + (dist.y * dist.y);
+  if (d > 1 || d < gRadIn || dot(sv, dist) < 0 || dot(ev, dist) > 0) {discard;}
   fColor = gColor;
 }

shader/twoD/arc.geom

@@ -5,32 +5,32 @@ in vec4 vColor [];
 in vec4 vparams [];
 out vec4 gColor;
 out float gRadIn;
-out float gRadOut;
-out vec2 cenPosT;
 out vec2 angles;
+out vec2 dist;
 
-uniform vec2 winSize;
-uniform float zoom;
+uniform mat4 worldMat;
 
 void main()
 {
   angles = vparams[0].xy;
-  vec3 cenPos = gl_in[0].gl_Position.xyz;
+  vec4 cenPos = gl_in[0].gl_Position;
   gColor = vColor[0];
-  float width = vparams[0].w * 0.5;
-  float rad = vparams[0].z;
-  gRadOut = (rad + width) * zoom * 2;
-  gRadIn  = (rad - width) * zoom * 2;
+  float width = vparams[0].w ;
+  float rad = vparams[0].z + width;
+  gRadIn  = 1 - width * 2 / rad;
+  // I am not currently sure why the multiplicand is 4 and not 2
 
-  cenPosT = vec2 ( (cenPos.x + 1) * 0.5 * winSize.x , (cenPos.y + 1) * 0.5 * winSize.y);
-
-  gl_Position = vec4 (cenPos.x + gRadOut/winSize.x, cenPos.y + gRadOut/winSize.y, cenPos.z , 1);
+  gl_Position = worldMat * vec4 (cenPos.x + rad, cenPos.y + rad, cenPos.z , 1);
+  dist = vec2 (1,1);
   EmitVertex();
-  gl_Position = vec4 (cenPos.x - gRadOut/winSize.x, cenPos.y + gRadOut/winSize.y, cenPos.z , 1);
+  gl_Position = worldMat * vec4 (cenPos.x - rad, cenPos.y + rad, cenPos.z , 1);
+  dist = vec2 (-1,1);
   EmitVertex();
-  gl_Position = vec4 (cenPos.x + gRadOut/winSize.x, cenPos.y - gRadOut/winSize.y, cenPos.z , 1);
+  gl_Position = worldMat * vec4 (cenPos.x + rad, cenPos.y - rad, cenPos.z , 1);
+  dist = vec2 (1,-1);
   EmitVertex();
-  gl_Position = vec4 (cenPos.x - gRadOut/winSize.x, cenPos.y - gRadOut/winSize.y, cenPos.z , 1);
+  gl_Position = worldMat * vec4 (cenPos.x - rad, cenPos.y - rad, cenPos.z , 1);
+  dist = vec2 (-1,-1);
   EmitVertex();
 
   EndPrimitive();

shader/twoD/arc.vert

@@ -13,7 +13,8 @@ uniform mat4 worldMat;
 
 void main()
 {
-  gl_Position = worldMat * vec4(position.xyz,1);
+  //gl_Position = worldMat * vec4(position.xyz,1);
+  gl_Position = vec4(position.xyz,1);
   vColor = color;
   vparams = saEaRadWdth;
 }

src/Dodge/Default.hs

@@ -95,7 +95,7 @@ defaultWorld = World
     , _midgroundDecorations = 
         [setDepth (-0.1) $ color orange $ pictures
             [ polygon $ rectNSEW 50 40 140 (-20)
-            , translate 60 45 $ thickArc 0 pi 75 10
+            , translate 60 45 $ scale 0.5 1 $  thickArc 0 pi 75 10
             ]
         ]
     }