Add shaders that will just return positional information

shader/posTwoD/bezierQuad.geom

@@ -0,0 +1,76 @@
+#version 430 core
+layout (triangles) in;
+layout (triangle_strip, max_vertices = 5) out;
+in vec4 vColor[];
+in vec2 vPosOff[];
+in float vRadMag[];
+out vec4 gColor;
+out float wStart;
+out float wEnd;
+out vec3 gBoundingBox;
+
+out vec2 box2 ;
+
+vec2 normV2 (vec2 v)
+{   return vec2(-v.y,v.x) ;
+}
+float lhs (vec2 da, vec2 db)
+{   return sign(dot(da, normV2(db))) ;
+}
+
+float extrapolate (vec2 inOne, vec2 inZeroA, vec2 inZeroB, vec2 xy)
+{ 
+    float det = inOne.x * (inZeroA.y - inZeroB.y)
+                + inZeroA.x * (inZeroB.y - inOne.y)
+                + inZeroB.x * (inOne.y   - inZeroA.y)
+                ;
+    float r = (inZeroA.y - inZeroB.y) ;
+    float s = (inZeroB.x - inZeroA.x) ;
+    float t = (inZeroA.x * inZeroB.y - inZeroB.x * inZeroA.y) ;
+    return r * xy.x + s * xy.y + t
+            / det ;
+}
+
+void main()
+{
+  vec3 pa = gl_in[0].gl_Position.xyz;
+  vec3 pb = gl_in[1].gl_Position.xyz;
+  vec3 pc = gl_in[2].gl_Position.xyz;
+
+  wStart = vRadMag [0];
+  wEnd   = vRadMag [2];
+
+  box2 = vec2 (1,0);
+  gBoundingBox = vec3 (0.9,0.1,0);
+  gColor = vColor[0];
+  gl_Position = vec4 (vPosOff[0] , pa.z , 1);
+  EmitVertex();
+  box2 = vec2 (0,1);
+  gBoundingBox = vec3 (0.1,0.9,0);
+  gColor = vColor[2];
+  gl_Position = vec4 (vPosOff[2] , pc.z , 1);
+  EmitVertex();
+  box2 = vec2( extrapolate(vPosOff[0],vPosOff[2],pb.xy,pa.xy)
+             , extrapolate(vPosOff[2],vPosOff[0],pb.xy,pa.xy)
+             ) ;
+  box2 = vec2(0.2,0);
+  gBoundingBox = vec3 (1,0,1);
+  gColor = vColor[0];
+  gl_Position = vec4 (pa, 1);
+  EmitVertex();
+  box2 = vec2( extrapolate(vPosOff[0],vPosOff[2],pb.xy,pc.xy)
+             , extrapolate(vPosOff[2],vPosOff[0],pb.xy,pc.xy)
+             ) ;
+  box2 = vec2(0,0.2);
+  gBoundingBox = vec3 (0,1,1);
+  gColor = vColor[2];
+  gl_Position = vec4 (pc, 1);
+  EmitVertex();
+  box2 = vec2( 0,0 ) ;
+  gBoundingBox = vec3 (0,0,0);
+  gColor = vColor[1];
+  gl_Position = vec4 (pb, 1);
+  EmitVertex();
+
+  EndPrimitive();
+}