Cleanup arc drawing

2023-01-11 00:21:06 +00:00
parent 471c6fec7e
commit 9796564075
4 changed files with 133 additions and 73 deletions
@@ -0,0 +1,49 @@
+module Picture.Arc where
+
+import Color
+import Geometry
+import Picture.Data
+
+-- this should work regardless of which angle is larger, though swapping the
+-- angles will affect the winding of the drawn triangles
+arcFull :: Float -> Float -> Color -> Float -> Float -> Color -> Float -> Color -> Picture
+arcFull startA swidth scol endA ewidth ecol r centercol
+    | abs (difference startA endA) > pi / 2 =
+        arcFull startA swidth scol midA mw mc r centercol
+            <> arcFull midA mw mc endA ewidth ecol r centercol
+    | otherwise = arcPart startA swidth scol endA ewidth ecol r centercol
+  where
+    midA = 0.5 * (startA + endA)
+    mw = 0.5 * (swidth + ewidth)
+    mc = mixColors 0.5 0.5 scol ecol
+
+-- should work if the angles are pi/2 or less apart.
+arcPart :: Float -> Float -> Color -> Float -> Float -> Color -> Float -> Color -> Picture
+arcPart startA sw sc endA ew ec r centercol =
+    map
+        f
+        [ (V3 0 0 0, centercol, V3 0 0 mwdth)
+        , (V3 xa ya 0, sc, V3 ad op wdth)
+        , (V3 xb yb 0, mc, V3 1 1 mwdth)
+        , (V3 0 0 0, centercol, V3 0 0 mwdth)
+        , (V3 xb yb 0, mc, V3 1 1 mwdth)
+        , (V3 xc yc 0, ec, V3 ad op ewdth)
+        ]
+  where
+    mc = mixColors 0.5 0.5 sc ec
+    ang = endA - startA
+    -- imagine that the arc is centered on the diagonal of the first quadrant
+    -- then the x-y values for the start and end of the arc are the following
+    op = sin ((pi / 2 - ang) / 2)
+    ad = cos ((pi / 2 - ang) / 2)
+    -- for most of the drawn triangles, the "width" value is interpolated towards the center
+    wdth = (wdth' + (wdth' - 1) * mwdth) / wdth'
+    wdth' = 1 - sw / r
+    -- along the middle line the "width" value is the following constant
+    mwdth = 1 - (0.5 * (sw + ew)) / r
+    ewdth' = 1 - ew / r
+    ewdth = (ewdth' + (ewdth' - 1) * mwdth) / ewdth'
+    (V2 xa ya) = rotateV startA (V2 r 0)
+    (V2 xb yb) = rotateV (0.5 * (startA + endA)) (V2 (r * sqrt 2) 0)
+    (V2 xc yc) = rotateV endA (V2 r 0)
+    f (pos, col, V3 a b c) = Verx pos col [a, b, c] BottomLayer arcNum