Add GMs for testing drawArc

gm/circulararcs.cpp

Index: gm/circulararcs.cpp
diff --git a/gm/circulararcs.cpp b/gm/circulararcs.cpp
new file mode 100644
index 0000000000000000000000000000000000000000..7bc40de3faecf02ffd5eb27aa1dbba6d702f4554
--- /dev/null
+++ b/gm/circulararcs.cpp
@@ -0,0 +1,102 @@
+/*
+ * Copyright 2016 Google Inc.
+ *
+ * Use of this source code is governed by a BSD-style license that can be
+ * found in the LICENSE file.
+ */
+
+#include <functional>
+#include "SkCanvas.h"
+#include "gm.h"
+
+static constexpr SkScalar kStarts[] = {0.f, 10.f, 30.f, 45.f, 90.f, 165.f, 180.f, 270.f};
+static constexpr SkScalar kSweeps[] = {45.f, 90.f, 165.f, 180.f, 220.f, 270.f, 300.f, 315.f};
+static constexpr SkScalar kDiameter = 40.f;
+static constexpr SkRect kRect = {0.f, 0.f, kDiameter, kDiameter};
+static constexpr int kW = 1000;
+static constexpr int kH = 1000;
+static constexpr SkScalar kPad = 20.f;
+
+void draw_arcs(SkCanvas* canvas, std::function<void(SkPaint*)> configureStyle) {
+    // Draws grid of arcs with different start/sweep angles in red and their complement arcs in
+    // blue.
+    auto drawGrid = [canvas, &configureStyle] (SkScalar x, SkScalar y, bool useCenter, bool aa) {
+        SkPaint p0;
+        p0.setColor(SK_ColorRED);
+        p0.setAntiAlias(aa);
+        // Set a reasonable stroke width that configureStyle can override.
+        p0.setStrokeWidth(15.f);
+        // Use alpha so we see magenta on overlap between arc and its complement.
+        p0.setAlpha(100);
+        SkPaint p1 = p0;
+        p1.setColor(SK_ColorBLUE);
+        configureStyle(&p0);
+        configureStyle(&p1);
+
+        canvas->save();
+        canvas->translate(kPad + x, kPad + y);
+        for (auto start : kStarts) {
+            canvas->save();
+            for (auto sweep : kSweeps) {
+                canvas->drawArc(kRect, start, sweep, useCenter, p0);
+                canvas->drawArc(kRect, start, -(360.f - sweep), useCenter, p1);
+                canvas->translate(kRect.width() + kPad, 0.f);
+            }
+            canvas->restore();
+            canvas->translate(0, kRect.height() + kPad);
+        }
+        canvas->restore();
+    };
+    // Draw a grids for combo of enabling/disabling aa and using center.
+    static constexpr SkScalar kGridW = kW / 2.f;
+    static constexpr SkScalar kGridH = kH / 2.f;
+    drawGrid(0.f   , 0.f   , false, false);
+    drawGrid(kGridW, 0.f   , true , false);
+    drawGrid(0.f   , kGridH, false, true );
+    drawGrid(kGridW, kGridH, true , true );
+    // Draw separators between the grids.
+    SkPaint linePaint;
+    linePaint.setAntiAlias(true);
+    linePaint.setColor(SK_ColorBLACK);
+    canvas->drawLine(kGridW, 0.f   , kGridW,            SkIntToScalar(kH), linePaint);
+    canvas->drawLine(0.f   , kGridH, SkIntToScalar(kW), kGridH,            linePaint);
+}
+
+#define DEF_ARC_GM(name) DEF_SIMPLE_GM(circular_arcs_##name, canvas, kW, kH)
+
+DEF_ARC_GM(circular_arcs_fill) {

[egdaniel, 2016/08/19 18:35:18]

the "circular_arcs_circular_arcs_fill" gm? somehow i feel like this name could
be shortened.

[bsalomon, 2016/08/19 18:52:35]

shoot, should be just fill here.

+    auto setFill = [] (SkPaint*p) { p->setStyle(SkPaint::kFill_Style); };
+    draw_arcs(canvas, setFill);
+}
+
+DEF_ARC_GM(hairline) {
+    auto setHairline = [] (SkPaint* p) {
+        p->setStyle(SkPaint::kStroke_Style);
+        p->setStrokeWidth(0.f);
+    };
+    draw_arcs(canvas, setHairline);
+}
+
+DEF_ARC_GM(stroke_butt) {
+    auto setStroke = [](SkPaint* p) {
+        p->setStyle(SkPaint::kStroke_Style);
+        p->setStrokeCap(SkPaint::kButt_Cap);
+    };
+    draw_arcs(canvas, setStroke);
+}
+
+DEF_ARC_GM(stroke_square) {
+    auto setStroke = [] (SkPaint* p) {
+        p->setStyle(SkPaint::kStroke_Style);
+        p->setStrokeCap(SkPaint::kSquare_Cap);
+    };
+    draw_arcs(canvas, setStroke);
+}
+
+DEF_ARC_GM(stroke_round) {
+    auto setStroke = [] (SkPaint* p) {
+        p->setStyle(SkPaint::kStroke_Style);
+        p->setStrokeCap(SkPaint::kRound_Cap);
+    };
+    draw_arcs(canvas, setStroke);
+}