Determine bug in bezier curve rendering

shader/bezierQuad.geom

@@ -1,6 +1,6 @@
 #version 430 core
 layout (triangles) in;
-layout (triangle_strip, max_vertices = 4) out;
+layout (triangle_strip, max_vertices = 5) out;
 in vec4 vColor[];
 in float vRad[];
 out vec4 gColor;
@@ -8,8 +8,11 @@ out float gRadStart;
 out float gRadEnd;
 out vec3 gBoundingBox;
 
-vec3 normV (vec3 v)
-{   return vec3(v.y,-v.x,v.z) ;
+vec2 normV2 (vec2 v)
+{   return vec2(-v.y,v.x) ;
+}
+float lhs (vec2 da, vec2 db)
+{   return sign(dot(da, normV2(db))) ;
 }
 
 void main()
@@ -21,21 +24,31 @@ void main()
   gRadStart = vRad[0];
   gRadEnd   = vRad[2];
 
+  vec2 ab = (pa.xy - pb.xy);
+  vec2 cb = (pc.xy - pb.xy);
+  float dir = lhs( cb,ab);
 
+  gBoundingBox = vec3 (0.9,0.1,0);
+  gColor = vColor[0];
+  gl_Position = vec4 (pa.xy + dir * 2 * gRadStart * normV2(ab) , pa.z , 1);
+  EmitVertex();
+  gBoundingBox = vec3 (0.1,0.9,0);
+  gColor = vColor[2];
+//  gl_Position = vec4 (pc.xy + dir * gRadEnd * (normV2 (pb.xy-pc.xy)), pa.z , 1);
+  gl_Position = vec4 (pc.xy - dir * 2 * gRadEnd * normV2(cb) , pc.z , 1);
+  EmitVertex();
   gBoundingBox = vec3 (1,0,1);
   gColor = vColor[0];
-  gl_Position = vec4 (pa + normV (pa-pb) , 1);
-  EmitVertex();
   gl_Position = vec4 (pa, 1);
   EmitVertex();
-  gBoundingBox = vec3 (0,0,0);
-  gColor = vColor[1];
-  gl_Position = vec4 (pb, 1);
-  EmitVertex();
   gBoundingBox = vec3 (0,1,1);
   gColor = vColor[2];
   gl_Position = vec4 (pc, 1);
   EmitVertex();
+  gBoundingBox = vec3 (0,0,0);
+  gColor = vColor[1];
+  gl_Position = vec4 (pb, 1);
+  EmitVertex();
 
   EndPrimitive();
 }

src/Dodge/Critters.hs

@@ -364,7 +364,6 @@ startCr = basicCreature
                             ,hvAutoGun
                             ,teslaGun
                             ,latchkey 0
-                            ,frontArmour
                             ,miniGun
                             ,medkit 50
                             ,bezierGun

src/Dodge/Rendering.hs

@@ -122,7 +122,7 @@ worldPictures w
 
 testPic :: World -> [Picture]
 testPic w = --[blank]
-     [setLayer 1 $ onLayerL [99] $ bezierQuad white red 20 50 (-200,0) (0,0) (200,50) ]
+     [setLayer 1 $ onLayerL [99] $ bezierQuad white red 20 20 (00,00) (200,200) (200,000) ]
     -- $ uncurry translate (mouseWorldPos w) 
 
 

src/Dodge/Rooms.hs

@@ -548,7 +548,7 @@ deadEndRoom = Room
                  ]
     , _rmLinks = lnks
     , _rmPath  = []
-    , _rmPS    = [PS (0,-10) 0 basicLS]
+    , _rmPS    = [PS (0,-20) 0 basicLS]
     , _rmBound = rectNSWE 20 (-20) (-30) 30
     }
     where lnks = [((0,30)  ,0)

src/Picture.hs

@@ -70,19 +70,22 @@ polygonCol :: [(Point2,RGBA)] -> Picture
 polygonCol = PolygonCol 0
 
 -- note that much of work computing the width of the bezier curve is done here
--- not sure that moving the control point does much...
 bezierQuad :: Color -> Color -> Float -> Float -> Point2 -> Point2 -> Point2 -> Picture
 bezierQuad cola colc ra rc a b c = BezierQuad 0 [(aX,cola                 ,raX)
-                                                ,(bx,mixColors 0.5 0.5 cola colc,1)
+                                                ,(bX,mixColors 0.5 0.5 cola colc,1)
                                                 ,(cX,colc                 ,rcX)]
-    where v = a -.- c
-          nv = normalizeV v
-          aX = a +.+ ra * 0.5 *.* nv
-          cX = c -.- rc * 0.5 *.* nv
-          raX = ra / magV (aX -.- cX)
-          rcX = rc / magV (aX -.- cX)
-          bx = b +.+ (0.5 * ra *.* normalizeV (b -.- a))
-                 +.+ (0.5 * rc *.* normalizeV (b -.- c))
+    where b2a | isLHS a b c = b -.- a
+              | otherwise   = a -.- b
+          nb2a = normalizeV $ vNormal b2a
+          aX = a +.+ ra * 0.5 *.* nb2a
+          b2c | isLHS a b c = c -.- b
+              | otherwise   = b -.- c
+          nb2c = normalizeV $ vNormal b2c
+          cX = c +.+ rc * 0.5 *.* nb2c
+          raX = ra / magV (aX -.- bX)
+          rcX = rc / magV (cX -.- bX)
+          bX = b +.+ (0.5 * ra *.* nb2a)
+                 +.+ (0.5 * rc *.* nb2c)
 
 color :: RGBA -> Picture -> Picture
 {-# INLINE color #-}