fix transform bug for Mathf.PI.

Runtime/rendering/object.cs

 
         public void pushTransform(bool needsCompositing, Offset offset, Matrix3 transform,
             PaintingContextCallback painter) {
-            var effectiveTransform = Matrix3.makeTrans(offset.dx, offset.dy);
-            effectiveTransform.preConcat(transform);
-            effectiveTransform.preTranslate(-offset.dx, -offset.dy);
+            Matrix3 effectiveTransform;
+            if (offset == null || offset == Offset.zero) {
+                effectiveTransform = transform;
+            } else {
+                effectiveTransform = Matrix3.makeTrans(offset.dx, offset.dy);
+                effectiveTransform.preConcat(transform);
+                effectiveTransform.preTranslate(-offset.dx, -offset.dy);
+            }
 
             if (needsCompositing) {
                 var inverse = Matrix3.I();

Runtime/ui/geometry.cs

                 Mathf.Floor(this.right), Mathf.Floor(this.bottom));
         }
 
+        public Rect normalize() {
+            if (this.left <= this.right && this.top <= this.bottom) {
+                return this;
+            }
+
+            return fromLTRB(
+                Mathf.Min(this.left, this.right),
+                Mathf.Min(this.top, this.bottom),
+                Mathf.Max(this.left, this.right),
+                Mathf.Max(this.top, this.bottom)
+            );
+        }
+
         public static Rect lerp(Rect a, Rect b, float t) {
             if (a == null && b == null) {
                 return null;

Runtime/ui/matrix.cs

                     src.top + ty,
                     src.right + tx,
                     src.bottom + ty
-                );
+                ).normalize();
 
                 return true;
             }
                 src.top * sy + ty,
                 src.right * sx + tx,
                 src.bottom * sy + ty
-            );
+            ).normalize();
         }
 
         public static bool operator ==(Matrix3 a, Matrix3 b) {