Compute pixel scale based on matrix max scale before doing the fill or storke. (#124)

src/pixie/paths.nim

@@ -34,6 +34,12 @@ type
 when defined(release):
   {.push checks: off.}
 
+proc maxScale(m: Mat3): float32 =
+  max(
+    vec2(m[0, 0], m[0, 1]).length,
+    vec2(m[1, 0], m[1, 1]).length
+  )
+
 proc parameterCount(kind: PathCommandKind): int =
   case kind:
   of Close: 0
@@ -495,7 +501,7 @@ proc polygon*(path: var Path, x, y, size: float32, sides: int) =
 proc polygon*(path: var Path, pos: Vec2, size: float32, sides: int) {.inline.} =
   path.polygon(pos.x, pos.y, size, sides)
 
-proc commandsToShapes*(path: Path): seq[seq[Vec2]] =
+proc commandsToShapes*(path: Path, pixelScale: float32 = 1.0): seq[seq[Vec2]] =
   ## Converts SVG-like commands to line segments.
 
   var
@@ -507,7 +513,7 @@ proc commandsToShapes*(path: Path): seq[seq[Vec2]] =
     prevCommandKind = Move
     prevCtrl, prevCtrl2: Vec2
 
-  const errorMargin = 0.2
+  let errorMargin = 0.2 / pixelScale
 
   proc addSegment(shape: var seq[Vec2], at, to: Vec2) =
     # Don't add any 0 length lines
@@ -1250,11 +1256,11 @@ proc strokeShapes(
     if strokeShape.len > 0:
       result.add(strokeShape)
 
-proc parseSomePath(path: SomePath): seq[seq[Vec2]] {.inline.} =
+proc parseSomePath(path: SomePath, pixelScale:float32 = 1.0): seq[seq[Vec2]] {.inline.} =
   when type(path) is string:
-    parsePath(path).commandsToShapes()
+    parsePath(path).commandsToShapes(pixelScale)
   elif type(path) is Path:
-    path.commandsToShapes()
+    path.commandsToShapes(pixelScale)
   elif type(path) is seq[seq[Segment]]:
     path
 
@@ -1275,7 +1281,11 @@ proc fillPath*(
   windingRule = wrNonZero,
   blendMode = bmNormal
 ) =
-  var shapes = parseSomePath(path)
+  when type(transform) is Mat3:
+    let pixelScale = transform.maxScale()
+  else:
+    let pixelScale = 1.0
+  var shapes = parseSomePath(path, pixelScale)
   for shape in shapes.mitems:
     for segment in shape.mitems:
       when type(transform) is Vec2:
@@ -1324,7 +1334,11 @@ proc strokePath*(
   strokeWidth = 1.0,
   blendMode = bmNormal
 ) =
-  var strokeShapes = strokeShapes(parseSomePath(path), strokeWidth)
+  when type(transform) is Mat3:
+    let pixelScale = transform.maxScale()
+  else:
+    let pixelScale = 1.0
+  var strokeShapes = strokeShapes(parseSomePath(path, pixelScale), strokeWidth)
   for shape in strokeShapes.mitems:
     for segment in shape.mitems:
       when type(transform) is Vec2:

tests/test_pixelScale_fill.nim

@@ -0,0 +1,11 @@
+import pixie
+
+let image = newImage(200, 200)
+image.fill(rgba(255, 255, 255, 255))
+
+var p = parsePath("M1 0.5C1 0.776142 0.776142 1 0.5 1C0.223858 1 0 0.776142 0 0.5C0 0.223858 0.223858 0 0.5 0C0.776142 0 1 0.223858 1 0.5Z")
+image.fillPath(p, rgba(255, 0, 0, 255), scale(vec2(200, 200)))
+
+image.strokePath(p, rgba(0, 255, 0, 255), scale(vec2(200, 200)), strokeWidth=0.01)
+
+image.writeFile("tests/images/paths/pixelScale.png")