Add svg path arcto

The arcto() used by SVG in Chrome and Android is ported here, using conics
instead of cubics. The logic is a direct transposition of the WebKit code.

The attached GM includes SVG that draws the same as Skia.

R=reed@google.com
BUG=skia:3959
GOLD_TRYBOT_URL= https://gold.skia.org/search2?unt=true&query=source_type%3Dgm&master=false&issue=1613303002

Review URL: https://codereview.chromium.org/1613303002

1 files changed, 86 insertions, 0 deletions

diff --git a/gm/arcto.cpp b/gm/arcto.cpp
new file mode 100644
index 0000000000..900c6b30ea
--- /dev/null
+++ b/gm/arcto.cpp
@@ -0,0 +1,86 @@
+/*
+ * Copyright 2016 Google Inc.
+ *
+ * Use of this source code is governed by a BD-style license that can be
+ * found in the LICENSE file.
+ */
+
+#include "gm.h"
+#include "SkParsePath.h"
+#include "SkPath.h"
+
+/*
+The arcto test below should draw the same as this SVG:
+(Note that Skia's arcTo Direction parameter value is opposite SVG's sweep value, e.g. 0 / 1)
+
+<svg width="500" height="600">
+<path d="M 50,100 A50,50,   0,0,1, 150,200" style="stroke:#660000; fill:none; stroke-width:2" />
+<path d="M100,100 A50,100,  0,0,1, 200,200" style="stroke:#660000; fill:none; stroke-width:2" />
+<path d="M150,100 A50,50,  45,0,1, 250,200" style="stroke:#660000; fill:none; stroke-width:2" />
+<path d="M200,100 A50,100, 45,0,1, 300,200" style="stroke:#660000; fill:none; stroke-width:2" />
+
+<path d="M150,200 A50,50,   0,1,0, 150,300" style="stroke:#660000; fill:none; stroke-width:2" />
+<path d="M200,200 A50,100,  0,1,0, 200,300" style="stroke:#660000; fill:none; stroke-width:2" />
+<path d="M250,200 A50,50,  45,1,0, 250,300" style="stroke:#660000; fill:none; stroke-width:2" />
+<path d="M300,200 A50,100, 45,1,0, 300,300" style="stroke:#660000; fill:none; stroke-width:2" />
+
+<path d="M250,400  A120,80 0 0,0 250,500"
+    fill="none" stroke="red" stroke-width="5" />
+
+<path d="M250,400  A120,80 0 1,1 250,500"
+    fill="none" stroke="green" stroke-width="5"/>
+
+<path d="M250,400  A120,80 0 1,0 250,500"
+    fill="none" stroke="purple" stroke-width="5"/>
+
+<path d="M250,400  A120,80 0 0,1 250,500"
+    fill="none" stroke="blue" stroke-width="5"/>
+</svg>
+ */
+
+DEF_SIMPLE_GM(arcto, canvas, 500, 600) {
+    SkPaint paint;
+    paint.setAntiAlias(true);
+    paint.setStyle(SkPaint::kStroke_Style);
+    paint.setStrokeWidth(2);
+    paint.setColor(0xFF660000);
+    canvas->scale(2, 2);
+    SkRect oval = SkRect::MakeXYWH(100, 100, 100, 100);
+    SkPath svgArc;
+
+    for (int angle = 0; angle <= 45; angle += 45) {
+       for (int oHeight = 2; oHeight >= 1; --oHeight) {
+            SkScalar ovalHeight = oval.height() / oHeight;
+            svgArc.moveTo(oval.fLeft, oval.fTop);
+            svgArc.arcTo(oval.width() / 2, ovalHeight, SkIntToScalar(angle), SkPath::kSmall_ArcSize,
+                    SkPath::kCW_Direction, oval.right(), oval.bottom());
+            canvas->drawPath(svgArc, paint);
+            svgArc.reset();
+
+            svgArc.moveTo(oval.fLeft + 100, oval.fTop + 100);
+            svgArc.arcTo(oval.width() / 2, ovalHeight, SkIntToScalar(angle), SkPath::kLarge_ArcSize,
+                    SkPath::kCCW_Direction, oval.right(), oval.bottom() + 100);
+            canvas->drawPath(svgArc, paint);
+            oval.offset(50, 0);
+            svgArc.reset();
+
+        }
+    }
+
+    paint.setStrokeWidth(5);
+    const SkColor purple = 0xFF800080;
+    const SkColor darkgreen = 0xFF008000;
+    const SkColor colors[] = { SK_ColorRED, darkgreen, purple, SK_ColorBLUE };
+    const char* arcstrs[] = {
+        "M250,400  A120,80 0 0,0 250,500",
+        "M250,400  A120,80 0 1,1 250,500",
+        "M250,400  A120,80 0 1,0 250,500",
+        "M250,400  A120,80 0 0,1 250,500"
+    };
+    int cIndex = 0;
+    for (const char* arcstr : arcstrs) {
+        SkParsePath::FromSVGString(arcstr, &svgArc);
+        paint.setColor(colors[cIndex++]);
+        canvas->drawPath(svgArc, paint);
+    }
+}