SkCanvas interface for drawing a patch.

src/utils/SkPatchUtils.cpp

Index: src/utils/SkPatchUtils.cpp
diff --git a/src/utils/SkPatchUtils.cpp b/src/utils/SkPatchUtils.cpp
new file mode 100644
index 0000000000000000000000000000000000000000..24428beb74f9e6ac6037ad765ae590aacf87b793
--- /dev/null
+++ b/src/utils/SkPatchUtils.cpp
@@ -0,0 +1,57 @@
+/*
+ * Copyright 2014 Google Inc.
+ *
+ * Use of this source code is governed by a BSD-style license that can be
+ * found in the LICENSE file.
+ */
+
+#include "SkPatchUtils.h"
+
+#include "SkGeometry.h"
+
+// size in pixels of each partition per axis, adjust this knob
+static const int kPartitionSize = 30;
+
+/**
+ * Calculate the approximate arc length given a bezier curve's control points.
+ */
+static SkScalar approx_arc_length(SkPoint* points, int count) {
+    if (count < 2) {
+        return 0;
+    }
+    SkScalar arcLength = 0;
+    for (int i = 0; i < count - 1; i++) {
+        arcLength += SkPoint::Distance(points[i], points[i + 1]);
+    }
+    return arcLength;
+}
+
+SkIPoint SkPatchUtils::GetLevelOfDetail(const SkPatch& patch, const SkMatrix* matrix) {
+    
+    SkPoint mapPts[12];
+    matrix->mapPoints(mapPts, patch.getControlPoints(), 12);
+    
+    // Approximate length of each cubic.
+    SkPoint pts[4];
+    patch.getTopPoints(pts);
+    matrix->mapPoints(pts, 4);
+    int topLength = approx_arc_length(pts, 4);
+    
+    patch.getBottomPoints(pts);
+    matrix->mapPoints(pts, 4);
+    int bottomLength = approx_arc_length(pts, 4);
+    
+    patch.getLeftPoints(pts);
+    matrix->mapPoints(pts, 4);
+    int leftLength = approx_arc_length(pts, 4);
+    
+    patch.getRightPoints(pts);
+    matrix->mapPoints(pts, 4);
+    int rightLength = approx_arc_length(pts, 4);
+    
+    // Level of detail per axis, based on the larger side between top and bottom or left and right
+    int lodX = SkMaxScalar(topLength, bottomLength) / kPartitionSize;
+    int lodY = SkMaxScalar(leftLength, rightLength) / kPartitionSize;
+    
+    return SkIPoint::Make(SkMax32(4, lodX), SkMax32(4, lodY));
+}