Add a test for wide butt caps

This tests the case where the stroke has butt caps and its width
significantly larger than the path itself. There seems to be some
uncertainty over what should actually be drawn in some of these cases,
as evidenced by the variable results from different path renderers
here.

Change-Id: I5b62ec446bfbba73d09ddb4eac710e338bedfc6e
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/296114
Commit-Queue: Chris Dalton <csmartdalton@google.com>
Reviewed-by: Mike Reed <reed@google.com>

Author: csmartdalton86

gm/widebuttcaps.cpp

@@ -0,0 +1,84 @@
+/*
+ * Copyright 2020 Google Inc.
+ *
+ * Use of this source code is governed by a BSD-style license that can be
+ * found in the LICENSE file.
+ */
+
+#include "gm/gm.h"
+#include "include/core/SkCanvas.h"
+#include "include/core/SkPath.h"
+#include "include/core/SkPoint.h"
+
+static constexpr float kStrokeWidth = 100;
+
+class WideButtCaps : public skiagm::GM {
+public:
+    WideButtCaps() {}
+
+protected:
+
+    SkString onShortName() override {
+        return SkString("widebuttcaps");
+    }
+
+    SkISize onISize() override {
+        return SkISize::Make(120 * 4, 120 * 3 + 140);
+    }
+
+    void onOnceBeforeDraw() override {
+        fStrokePaint.setAntiAlias(true);
+        fStrokePaint.setStrokeWidth(kStrokeWidth);
+        fStrokePaint.setColor(SK_ColorGREEN);
+        fStrokePaint.setStyle(SkPaint::kStroke_Style);
+    }
+
+    void onDraw(SkCanvas* canvas) override {
+        SkAutoCanvasRestore arc(canvas, true);
+        canvas->translate(60, 60);
+        canvas->clear(SK_ColorBLACK);
+
+        this->drawStrokes(canvas,
+                SkPath().lineTo(10,0).lineTo(10,10),
+                SkPath().cubicTo(10,0, 10,0, 10,10));
+        canvas->translate(0, 120);
+
+        this->drawStrokes(canvas,
+                SkPath().lineTo(0,-10).lineTo(0,10),
+                SkPath().cubicTo(0,-10, 0,-10, 0,10));
+        canvas->translate(0, 120);
+
+        this->drawStrokes(canvas,
+                SkPath().lineTo(0,-10).lineTo(10,-10).lineTo(10,10).lineTo(0,10),
+                SkPath().cubicTo(0,-10, 10,10, 0,10));
+        canvas->translate(0, 140);
+
+        this->drawStrokes(canvas,
+                SkPath().lineTo(0,-10).lineTo(10,-10).lineTo(10,0).lineTo(0,0),
+                SkPath().cubicTo(0,-10, 10,0, 0,0));
+        canvas->translate(0, 120);
+    }
+
+    void drawStrokes(SkCanvas* canvas, const SkPath& path, const SkPath& cubic) {
+        SkAutoCanvasRestore arc(canvas, true);
+        fStrokePaint.setStrokeJoin(SkPaint::kBevel_Join);
+        canvas->drawPath(path, fStrokePaint);
+
+        canvas->translate(120, 0);
+        fStrokePaint.setStrokeJoin(SkPaint::kRound_Join);
+        canvas->drawPath(path, fStrokePaint);
+
+        canvas->translate(120, 0);
+        fStrokePaint.setStrokeJoin(SkPaint::kMiter_Join);
+        canvas->drawPath(path, fStrokePaint);
+
+        canvas->translate(120, 0);
+        canvas->drawPath(cubic, fStrokePaint);
+    }
+
+private:
+    SkPaint fStrokePaint;
+    typedef GM INHERITED;
+};
+
+DEF_GM( return new WideButtCaps; )

gn/gm.gni

@@ -386,6 +386,7 @@ gm_sources = [
   "$_gm/vertices.cpp",
   "$_gm/verylargebitmap.cpp",
   "$_gm/wacky_yuv_formats.cpp",
+  "$_gm/widebuttcaps.cpp",
   "$_gm/windowrectangles.cpp",
   "$_gm/xfermodeimagefilter.cpp",
   "$_gm/xfermodes.cpp",