cull zero-sized rects in ui.Canvas when filling them

Author: flar

lib/ui/painting.dart

@@ -5857,6 +5857,9 @@ base class _NativeCanvas extends NativeFieldWrapperClass1 implements Canvas {
   void clipRect(Rect rect, { ClipOp clipOp = ClipOp.intersect, bool doAntiAlias = true }) {
     assert(_rectIsValid(rect));
     rect = _sorted(rect);
+    // Even if rect is still empty - which implies it has a zero dimension -
+    // we still need to perform the clipRect operation as it will effectively
+    // nullify any further rendering until the next restore call.
     _clipRect(rect.left, rect.top, rect.right, rect.bottom, clipOp.index, doAntiAlias);
   }
 
@@ -5930,7 +5933,9 @@ base class _NativeCanvas extends NativeFieldWrapperClass1 implements Canvas {
   void drawRect(Rect rect, Paint paint) {
     assert(_rectIsValid(rect));
     rect = _sorted(rect);
-    _drawRect(rect.left, rect.top, rect.right, rect.bottom, paint._objects, paint._data);
+    if (paint.style != PaintingStyle.fill || !rect.isEmpty) {
+      _drawRect(rect.left, rect.top, rect.right, rect.bottom, paint._objects, paint._data);
+    }
   }
 
   @Native<Void Function(Pointer<Void>, Double, Double, Double, Double, Handle, Handle)>(symbol: 'Canvas::drawRect')
@@ -5959,7 +5964,9 @@ base class _NativeCanvas extends NativeFieldWrapperClass1 implements Canvas {
   void drawOval(Rect rect, Paint paint) {
     assert(_rectIsValid(rect));
     rect = _sorted(rect);
-    _drawOval(rect.left, rect.top, rect.right, rect.bottom, paint._objects, paint._data);
+    if (paint.style != PaintingStyle.fill || !rect.isEmpty) {
+      _drawOval(rect.left, rect.top, rect.right, rect.bottom, paint._objects, paint._data);
+    }
   }
 
   @Native<Void Function(Pointer<Void>, Double, Double, Double, Double, Handle, Handle)>(symbol: 'Canvas::drawOval')

testing/dart/canvas_test.dart

@@ -568,37 +568,71 @@ void main() async {
         ..color = color
         ..strokeWidth = 5.0;
 
+      final Rect tallThin = Rect.fromLTRB(
+        min(rect.left, rect.right) - 10,
+        rect.top,
+        min(rect.left, rect.right) - 10,
+        rect.bottom,
+      );
+      final Rect wideThin = Rect.fromLTRB(
+        rect.left,
+        min(rect.top, rect.bottom) - 10,
+        rect.right,
+        min(rect.top, rect.bottom) - 10,
+      );
+
       canvas.save();
       canvas.translate(x, y);
 
       paint.style = PaintingStyle.fill;
       canvas.drawRect(rect, paint);
+      canvas.drawRect(tallThin, paint);
+      canvas.drawRect(wideThin, paint);
 
       canvas.save();
       canvas.translate(0, 100);
       paint.style = PaintingStyle.stroke;
       canvas.drawRect(rect, paint);
+      canvas.drawRect(tallThin, paint);
+      canvas.drawRect(wideThin, paint);
       canvas.restore();
 
-
       canvas.save();
       canvas.translate(100, 0);
       paint.style = PaintingStyle.fill;
       canvas.drawOval(rect, paint);
+      canvas.drawOval(tallThin, paint);
+      canvas.drawOval(wideThin, paint);
       canvas.restore();
 
       canvas.save();
       canvas.translate(100, 100);
       paint.style = PaintingStyle.stroke;
       canvas.drawOval(rect, paint);
+      canvas.drawOval(tallThin, paint);
+      canvas.drawOval(wideThin, paint);
       canvas.restore();
 
       canvas.save();
       canvas.translate(50, 50);
+
+      canvas.save();
       canvas.clipRect(rect);
       canvas.drawPaint(paint);
       canvas.restore();
 
+      canvas.save();
+      canvas.clipRect(tallThin);
+      canvas.drawPaint(paint);
+      canvas.restore();
+
+      canvas.save();
+      canvas.clipRect(wideThin);
+      canvas.drawPaint(paint);
+      canvas.restore();
+
+      canvas.restore();
+
       canvas.restore();
     }