Refactor arc shader so it uses only matrix uniform

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();