use quads for mixed radius rrects

src/core/SkPath.cpp

Index: src/core/SkPath.cpp
diff --git a/src/core/SkPath.cpp b/src/core/SkPath.cpp
index 60cfe0373c08628573cf5be16ff829f428e7cd0f..9bcf18c8f7ba85a84679c0aaf290b94603ab71ec 100644
--- a/src/core/SkPath.cpp
+++ b/src/core/SkPath.cpp
@@ -950,41 +950,6 @@ static int build_arc_points(const SkRect& oval, SkScalar startAngle,
                           &matrix, pts);
 }
 
-static void add_corner_arc(SkPath* path, const SkRect& rect,
-                           SkScalar rx, SkScalar ry, int startAngle,
-                           SkPath::Direction dir, bool forceMoveTo) {
-    // These two asserts are not sufficient, since really we want to know
-    // that the pair of radii (e.g. left and right, or top and bottom) sum
-    // to <= dimension, but we don't have that data here, so we just have
-    // these conservative asserts.
-    SkASSERT(0 <= rx && rx <= rect.width());
-    SkASSERT(0 <= ry && ry <= rect.height());
-
-    SkRect   r;
-    r.set(-rx, -ry, rx, ry);
-
-    switch (startAngle) {
-        case   0:
-            r.offset(rect.fRight - r.fRight, rect.fBottom - r.fBottom);
-            break;
-        case  90:
-            r.offset(rect.fLeft - r.fLeft,   rect.fBottom - r.fBottom);
-            break;
-        case 180: r.offset(rect.fLeft - r.fLeft,   rect.fTop - r.fTop); break;
-        case 270: r.offset(rect.fRight - r.fRight, rect.fTop - r.fTop); break;
-        default: SkDEBUGFAIL("unexpected startAngle in add_corner_arc");
-    }
-
-    SkScalar start = SkIntToScalar(startAngle);
-    SkScalar sweep = SkIntToScalar(90);
-    if (SkPath::kCCW_Direction == dir) {
-        start += sweep;
-        sweep = -sweep;
-    }
-
-    path->arcTo(r, start, sweep, forceMoveTo);
-}
-
 void SkPath::addRoundRect(const SkRect& rect, const SkScalar radii[],
                           Direction dir) {
     SkRRect rrect;
@@ -992,6 +957,131 @@ void SkPath::addRoundRect(const SkRect& rect, const SkScalar radii[],
     this->addRRect(rrect, dir);
 }
 
+/* The inline clockwise and counterclockwise round rect quad approximations
+   make it easier to see the symmetry patterns used by add corner quads.
+Clockwise                                                     corner value
+    path->lineTo(rect.fLeft,           rect.fTop    + ry);    0 upper left
+    path->quadTo(rect.fLeft,           rect.fTop    + offPtY,
+                 rect.fLeft  + midPtX, rect.fTop    + midPtY);
+    path->quadTo(rect.fLeft  + offPtX, rect.fTop,
+                 rect.fLeft  + rx,     rect.fTop);
+
+    path->lineTo(rect.fRight - rx,     rect.fTop);            1 upper right
+    path->quadTo(rect.fRight - offPtX, rect.fTop,
+                 rect.fRight - midPtX, rect.fTop    + midPtY);
+    path->quadTo(rect.fRight,          rect.fTop    + offPtY,
+                 rect.fRight,          rect.fTop    + ry);
+
+    path->lineTo(rect.fRight,          rect.fBottom - ry);    2 lower right
+    path->quadTo(rect.fRight,          rect.fBottom - offPtY,
+                 rect.fRight - midPtX, rect.fBottom - midPtY);
+    path->quadTo(rect.fRight - offPtX, rect.fBottom,
+                 rect.fRight - rx,     rect.fBottom);
+
+    path->lineTo(rect.fLeft  + rx,     rect.fBottom);         3 lower left
+    path->quadTo(rect.fLeft  + offPtX, rect.fBottom,
+                 rect.fLeft  + midPtX, rect.fBottom - midPtY);
+    path->quadTo(rect.fLeft,           rect.fBottom - offPtY,
+                 rect.fLeft,           rect.fBottom - ry);
+
+Counterclockwise
+    path->lineTo(rect.fLeft,           rect.fBottom - ry);    3 lower left
+    path->quadTo(rect.fLeft,           rect.fBottom - offPtY,
+                 rect.fLeft  + midPtX, rect.fBottom - midPtY);
+    path->quadTo(rect.fLeft  + offPtX, rect.fBottom,
+                 rect.fLeft  + rx,     rect.fBottom);
+
+    path->lineTo(rect.fRight - rx,     rect.fBottom);         2 lower right
+    path->quadTo(rect.fRight - offPtX, rect.fBottom,
+                 rect.fRight - midPtX, rect.fBottom - midPtY);
+    path->quadTo(rect.fRight,          rect.fBottom - offPtY,
+                 rect.fRight,          rect.fBottom - ry);
+
+    path->lineTo(rect.fRight,          rect.fTop    + ry);    1 upper right
+    path->quadTo(rect.fRight,          rect.fTop    + offPtY,
+                 rect.fRight - midPtX, rect.fTop    + midPtY);
+    path->quadTo(rect.fRight - offPtX, rect.fTop,
+                 rect.fRight - rx,     rect.fTop);
+
+    path->lineTo(rect.fLeft  + rx,     rect.fTop);            0 upper left
+    path->quadTo(rect.fLeft  + offPtX, rect.fTop,
+                 rect.fLeft  + midPtX, rect.fTop    + midPtY);
+    path->quadTo(rect.fLeft,           rect.fTop    + offPtY,
+                 rect.fLeft,           rect.fTop    + ry);
+*/

[robertphillips, 2013/11/05 16:47:56]

Would it make sense to pass in the SkRRect itself (and use corner to get the
right radii) rather than bounds and radii separately?

[caryclark, 2013/11/05 20:29:55]

Done.

+static void add_corner_quads(SkPath* path, const SkRect& rect, const SkVector& radii,
+                             SkRRect::Corner corner, SkPath::Direction dir) {
+    SkScalar rx = radii.fX;
+    SkScalar ry = radii.fY;
+    // The mid point of the quadratic arc approximation is half way between the two
+    // control points. The float epsilon adjustment moves the on curve point out by
+    // two bits, distributing the convex test error between the round rect approximation
+    // and the convex cross product sign equality test.
+    SkScalar midPtX = rx - rx * (SK_Scalar1 + SK_ScalarTanPIOver8 + FLT_EPSILON * 4) / 2;
+    SkScalar midPtY = ry - ry * (SK_Scalar1 + SK_ScalarTanPIOver8 + FLT_EPSILON * 4) / 2;
+    SkScalar offPtX = rx - rx * SK_ScalarTanPIOver8;
+    SkScalar offPtY = ry - ry * SK_ScalarTanPIOver8;
+    static const int kCornerPts = 5;
+    SkScalar xOff[kCornerPts];
+    SkScalar yOff[kCornerPts];
+
+    if ((corner & 1) == (dir == SkPath::kCCW_Direction)) {  // corners always alternate direction
+        SkASSERT(dir == SkPath::kCCW_Direction
+             ? corner == SkRRect::kLowerLeft_Corner || corner == SkRRect::kUpperRight_Corner
+             : corner == SkRRect::kUpperLeft_Corner || corner == SkRRect::kLowerRight_Corner);
+        xOff[0] = xOff[1] = 0;
+        xOff[2] = midPtX;
+        xOff[3] = offPtX;
+        xOff[4] = rx;
+        yOff[0] = ry;
+        yOff[1] = offPtY;
+        yOff[2] = midPtY;
+        yOff[3] = yOff[4] = 0;
+    } else {
+        xOff[0] = rx;
+        xOff[1] = offPtX;
+        xOff[2] = midPtX;
+        xOff[3] = xOff[4] = 0;
+        yOff[0] = yOff[1] = 0;
+        yOff[2] = midPtY;
+        yOff[3] = offPtY;
+        yOff[4] = ry;
+    }
+    if ((corner - 1) & 2) {
+        SkASSERT(corner == SkRRect::kLowerLeft_Corner || corner == SkRRect::kUpperLeft_Corner);
+        for (int i = 0; i < kCornerPts; ++i) {
+            xOff[i] = rect.fLeft + xOff[i];  // cw lower right, lower left
+        }
+    } else {
+        SkASSERT(corner == SkRRect::kLowerRight_Corner || corner == SkRRect::kUpperRight_Corner);
+        for (int i = 0; i < kCornerPts; ++i) {
+            xOff[i] = rect.fRight - xOff[i];
+        }
+    }
+    if (corner < SkRRect::kLowerRight_Corner) {
+        for (int i = 0; i < kCornerPts; ++i) {
+            yOff[i] = rect.fTop + yOff[i];
+        }
+    } else {
+        for (int i = 0; i < kCornerPts; ++i) {
+            yOff[i] = rect.fBottom - yOff[i];
+        }
+    }
+
+    SkPoint lastPt;
+    SkAssertResult(path->getLastPt(&lastPt));
+    if (lastPt.fX != xOff[0] || lastPt.fY != yOff[0]) {
+        path->lineTo(xOff[0], yOff[0]);
+    }
+    if (rx || ry) {
+        path->quadTo(xOff[1], yOff[1], xOff[2], yOff[2]);
+        path->quadTo(xOff[3], yOff[3], xOff[4], yOff[4]);
+    } else {
+        path->lineTo(xOff[2], yOff[2]);
+        path->lineTo(xOff[4], yOff[4]);
+    }
+}
+
 void SkPath::addRRect(const SkRRect& rrect, Direction dir) {
     assert_known_direction(dir);
 
@@ -1009,18 +1099,23 @@ void SkPath::addRRect(const SkRRect& rrect, Direction dir) {
         const SkVector& rad = rrect.getSimpleRadii();
         this->addRoundRect(bounds, rad.x(), rad.y(), dir);
     } else {
+        fDirection = this->hasOnlyMoveTos() ? dir : kUnknown_Direction;
+
         SkAutoPathBoundsUpdate apbu(this, bounds);
 
+        this->incReserve(21);
         if (kCW_Direction == dir) {

[robertphillips, 2013/11/05 16:47:56]

Should 0 be 3 here? One of the Corner enum values could help with clarity.

[caryclark, 2013/11/05 20:29:55]

Done.

-            add_corner_arc(this, bounds, rrect.fRadii[0].fX, rrect.fRadii[0].fY, 180, dir, true);
-            add_corner_arc(this, bounds, rrect.fRadii[1].fX, rrect.fRadii[1].fY, 270, dir, false);
-            add_corner_arc(this, bounds, rrect.fRadii[2].fX, rrect.fRadii[2].fY,   0, dir, false);
-            add_corner_arc(this, bounds, rrect.fRadii[3].fX, rrect.fRadii[3].fY,  90, dir, false);
+            this->moveTo(bounds.fLeft, bounds.fBottom - rrect.fRadii[0].fY);  // bottom-left
+            add_corner_quads(this, bounds, rrect.fRadii[0], SkRRect::kUpperLeft_Corner, dir);
+            add_corner_quads(this, bounds, rrect.fRadii[1], SkRRect::kUpperRight_Corner, dir);
+            add_corner_quads(this, bounds, rrect.fRadii[2], SkRRect::kLowerRight_Corner, dir);
+            add_corner_quads(this, bounds, rrect.fRadii[3], SkRRect::kLowerLeft_Corner, dir);
         } else {
-            add_corner_arc(this, bounds, rrect.fRadii[0].fX, rrect.fRadii[0].fY, 180, dir, true);
-            add_corner_arc(this, bounds, rrect.fRadii[3].fX, rrect.fRadii[3].fY,  90, dir, false);
-            add_corner_arc(this, bounds, rrect.fRadii[2].fX, rrect.fRadii[2].fY,   0, dir, false);
-            add_corner_arc(this, bounds, rrect.fRadii[1].fX, rrect.fRadii[1].fY, 270, dir, false);
+            this->moveTo(bounds.fLeft, bounds.fTop + rrect.fRadii[0].fY);  // top-left
+            add_corner_quads(this, bounds, rrect.fRadii[3], SkRRect::kLowerLeft_Corner, dir);
+            add_corner_quads(this, bounds, rrect.fRadii[2], SkRRect::kLowerRight_Corner, dir);
+            add_corner_quads(this, bounds, rrect.fRadii[1], SkRRect::kUpperRight_Corner, dir);
+            add_corner_quads(this, bounds, rrect.fRadii[0], SkRRect::kUpperLeft_Corner, dir);
         }
         this->close();
     }