Fix COLRv1 sweeps modulo and paint clipping

Lib/blackrenderer/backends/cairo.py

@@ -174,6 +174,9 @@ def drawPathSweepGradient(
             useGouraudShading=False,
             extendMode=extendMode,
         )
+        if not patches:
+            self.context.restore()
+            return
         for (P0, color0), C0, C1, (P1, color1) in patches:
             # draw patch
             pat.begin_patch()

Lib/blackrenderer/backends/coregraphics.py

@@ -11,7 +11,8 @@
 _compositeModeMap = {
     CompositeMode.CLEAR: CG.kCGBlendModeClear,
     CompositeMode.SRC: CG.kCGBlendModeCopy,
-    CompositeMode.DEST: CG.kCGBlendModeNormal,  # This is wrong, but is worked around in canvas.compositeMode()
+    # This is wrong, but is worked around in canvas.compositeMode().
+    CompositeMode.DEST: CG.kCGBlendModeNormal,
     CompositeMode.SRC_OVER: CG.kCGBlendModeNormal,
     CompositeMode.DEST_OVER: CG.kCGBlendModeDestinationOver,
     CompositeMode.SRC_IN: CG.kCGBlendModeSourceIn,
@@ -233,6 +234,8 @@ def drawPathSweepGradient(
                 useGouraudShading=True,
                 extendMode=extendMode,
             )
+            if not patches:
+                return
             CG.CGContextBeginTransparencyLayer(self.context, None)
             CG.CGContextSetAllowsAntialiasing(self.context, False)
             for (P0, color0), (P1, color1) in patches:

Lib/blackrenderer/backends/pathCollector.py

@@ -36,7 +36,7 @@ def transform(self, transform):
         self.currentTransform = self.currentTransform.transform(transform)
 
     def clipPath(self, path):
-        self._addPath(path)
+        pass
 
     def drawPathSolid(self, path, color):
         self._addPath(path)

Lib/blackrenderer/backends/skia.py

@@ -159,8 +159,10 @@ def drawPathSweepGradient(
         gradientTransform,
     ):
         colorLine, startAngle, endAngle = normalizeSweepColorLineAndAngles(
-            colorLine, startAngle, endAngle
+            colorLine, startAngle, endAngle, extendMode
         )
+        if not colorLine:
+            return
         matrix = skia.Matrix()
         matrix.setAffine(gradientTransform)
         colors, stops = _unpackColorLine(colorLine)
@@ -169,7 +171,7 @@ def drawPathSweepGradient(
             cy=center[1],
             colors=colors,
             positions=stops,
-            mode=_extendModeMap[extendMode],
+            mode=skia.TileMode.kClamp,
             startAngle=startAngle,
             endAngle=endAngle,
             localMatrix=matrix,

Lib/blackrenderer/backends/svg.py

@@ -138,7 +138,7 @@ def _addElement(self, fillPath, fillTransform, paint, gradientTransform):
             if len(self.clipStack) > 1:
                 # FIXME: intersect clip paths with pathops
                 self._warn(
-                    "nested_clip"
+                    "nested_clip",
                     "SVG canvas does not support more than two nested clip paths"
                 )
             if clipTransform is not None:

Lib/blackrenderer/backends/sweepGradient.py

@@ -1,4 +1,4 @@
-from math import pi, ceil, floor, sin, cos, radians
+from math import pi, ceil, floor, sin, cos, radians, isclose
 from fontTools.misc.vector import Vector
 from fontTools.ttLib.tables.otTables import ExtendMode
 
@@ -34,16 +34,10 @@ def buildSweepGradientPatches(
         360° circle."""
 
     colorLine, startAngle, endAngle = normalizeSweepColorLineAndAngles(
-        colorLine, startAngle, endAngle
+        colorLine, startAngle, endAngle, extendMode
     )
-
-    angleRange = endAngle - startAngle
-
-    # Extend the color line to cover the full 360° circle if needed
-    if extendMode is not None and angleRange < 360:
-        colorLine, startAngle, endAngle = _extendColorLineForFullCircle(
-            colorLine, startAngle, endAngle, angleRange, extendMode
-        )
+    if not colorLine:
+        return []
 
     return _buildPatches(
         colorLine,
@@ -56,77 +50,84 @@ def buildSweepGradientPatches(
     )
 
 
-def normalizeSweepColorLineAndAngles(colorLine, startAngle, endAngle):
+def normalizeSweepColorLineAndAngles(colorLine, startAngle, endAngle, extendMode=None):
+    colorLine = _normalizeCoincidentStops(colorLine, extendMode)
+    if not colorLine:
+        return [], 0, 0
+
+    if _anglesCoincident(startAngle, endAngle):
+        if extendMode in (ExtendMode.REPEAT, ExtendMode.REFLECT):
+            return [], 0, 0
+        if extendMode == ExtendMode.PAD:
+            return _padColorLineForCoincidentAngles(colorLine, startAngle), 0, 360
+
     # When endAngle < startAngle, the sweep covers the arc going clockwise.
     # Our backends consume increasing angles, so swap angles and reverse the
     # color line to draw the same color rays.
     if endAngle < startAngle:
         startAngle, endAngle = endAngle, startAngle
         colorLine = [(1.0 - stop, color) for stop, color in reversed(colorLine)]
 
-    # Normalize angles to [0, 360) range and ensure startAngle < endAngle.
-    startAngle %= 360
-    endAngle %= 360
-    if startAngle >= endAngle:
-        endAngle += 360
+    if extendMode is not None:
+        colorLine = _colorLineForDrawingTurn(
+            colorLine, startAngle, endAngle, extendMode
+        )
+        return colorLine, 0, 360
 
     return colorLine, startAngle, endAngle
 
 
-def _extendColorLineForFullCircle(
-    colorLine, startAngle, endAngle, angleRange, extendMode
-):
-    """Extend the color line to cover a full 360° circle based on the extend mode.
-
-    Returns (newColorLine, newStartAngle, newEndAngle).
-    """
-    newColorLine = []
-    for angle0, angle1, wrapOffset in _splitSweepSegments(
-        startAngle, endAngle, extendMode
-    ):
-        if angle1 <= angle0:
-            continue
-
-        t0 = (angle0 + wrapOffset - startAngle) / angleRange
-        t1 = (angle1 + wrapOffset - startAngle) / angleRange
-        segmentSamples = _extendedSegmentSamples(colorLine, t0, t1, extendMode)
-
-        for t, color in segmentSamples:
-            angle = startAngle + t * angleRange - wrapOffset
-            if angle0 <= angle <= angle1:
-                newColorLine.append((angle / 360.0, color))
-
-    newColorLine.sort(key=lambda item: item[0])
-    return newColorLine, 0, 360
-
-
-def _splitSweepSegments(startAngle, endAngle, extendMode):
-    """Return one-turn angle segments with the correct shader t mapping.
-
-    Sweep shader angles live in the 0°..360° turn. If the sweep crosses the
-    angle wrap, angles from 0° to endAngle % 360 are part of the in-range
-    sector and must be evaluated with a +360° offset. Angles between the
-    wrapped end and the start are before the start, not after the end.
-    """
-    if endAngle <= 360:
-        return (
-            (0, startAngle, 0),
-            (startAngle, endAngle, 0),
-            (endAngle, 360, 0),
-        )
-
-    if extendMode == ExtendMode.PAD:
-        return (
-            (0, startAngle, 0),
-            (startAngle, 360, 0),
-        )
-
-    wrappedEnd = endAngle - 360
-    return (
-        (0, wrappedEnd, 360),
-        (wrappedEnd, startAngle, 0),
-        (startAngle, 360, 0),
-    )
+def _normalizeCoincidentStops(colorLine, extendMode):
+    if not colorLine:
+        return []
+    if not all(isclose(stop, colorLine[0][0], abs_tol=1e-9) for stop, _ in colorLine):
+        return colorLine
+    if extendMode in (ExtendMode.REPEAT, ExtendMode.REFLECT):
+        return []
+    if extendMode != ExtendMode.PAD:
+        return colorLine
+
+    offset = max(0, min(1, colorLine[0][0]))
+    firstColor = colorLine[0][1]
+    lastColor = colorLine[-1][1]
+    return [
+        (0, firstColor),
+        (offset, firstColor),
+        (offset, lastColor),
+        (1, lastColor),
+    ]
+
+
+def _anglesCoincident(startAngle, endAngle):
+    return isclose(startAngle, endAngle, abs_tol=1e-9)
+
+
+def _padColorLineForCoincidentAngles(colorLine, startAngle):
+    angle = (startAngle % 360) / 360.0
+    firstColor = colorLine[0][1]
+    lastColor = colorLine[-1][1]
+    return [
+        (0, firstColor),
+        (angle, firstColor),
+        (angle, lastColor),
+        (1, lastColor),
+    ]
+
+
+def _colorLineForDrawingTurn(colorLine, startAngle, endAngle, extendMode):
+    angleRange = endAngle - startAngle
+    if angleRange <= 0:
+        return []
+
+    t0 = (0 - startAngle) / angleRange
+    t1 = (360 - startAngle) / angleRange
+    samples = _extendedSegmentSamples(colorLine, t0, t1, extendMode)
+    colorLine = [
+        ((startAngle + t * angleRange) / 360.0, color)
+        for t, color in samples
+    ]
+    colorLine.sort(key=lambda item: item[0])
+    return colorLine
 
 
 def _extendedSegmentSamples(colorLine, t0, t1, extendMode):

Lib/blackrenderer/font.py

@@ -129,15 +129,9 @@ def colrV1GlyphNames(self):
     def getGlyphBounds(self, glyphName):
         if glyphName in self.colrV1Glyphs:
             bounds = self._getGlyphBounds(glyphName)
-            if self.clipBoxes is not None:
-                box = self.clipBoxes.get(glyphName)
-                if box is not None:
-                    if (
-                        box.Format == ClipBoxFormat.Variable
-                        and self.instancer is not None
-                    ):
-                        box = VarTableWrapper(box, self.instancer, self.varIndexMap)
-                    bounds = box.xMin, box.yMin, box.xMax, box.yMax
+            box = self._getClipBox(glyphName)
+            if box is not None:
+                bounds = box.xMin, box.yMin, box.xMax, box.yMax
         elif glyphName in self.colrV0Glyphs:
             # For COLRv0, we take the union of all layer bounds
             bounds = None
@@ -187,7 +181,8 @@ def _drawGlyphCOLRv1(self, glyph, canvas):
             raise RecursionError(f"Glyph '{glyph.BaseGlyph}' references itself")
         self._recursionCheck.add(glyph.BaseGlyph)
         try:
-            self._drawPaint(glyph.Paint, canvas)
+            with self._ensureClipBox(glyph.BaseGlyph, canvas):
+                self._drawPaint(glyph.Paint, canvas)
         finally:
             self._recursionCheck.remove(glyph.BaseGlyph)
 
@@ -409,6 +404,35 @@ def _ensureClipAndPushPath(self, canvas, path):
         self.currentPath = currentPath
         self.currentTransform = currentTransform
 
+    @contextmanager
+    def _ensureClipBox(self, glyphName, canvas):
+        box = self._getClipBox(glyphName)
+        if box is None:
+            yield
+            return
+
+        path = canvas.newPath()
+        path.moveTo((box.xMin, box.yMin))
+        path.lineTo((box.xMin, box.yMax))
+        path.lineTo((box.xMax, box.yMax))
+        path.lineTo((box.xMax, box.yMin))
+        path.closePath()
+        with canvas.savedState():
+            canvas.clipPath(path)
+            yield
+
+    def _getClipBox(self, glyphName):
+        if self.clipBoxes is None:
+            return None
+        box = self.clipBoxes.get(glyphName)
+        if (
+            box is not None
+            and box.Format == ClipBoxFormat.Variable
+            and self.instancer is not None
+        ):
+            box = VarTableWrapper(box, self.instancer, self.varIndexMap)
+        return box
+
     @contextmanager
     def _savedTransform(self):
         savedTransform = self.currentTransform