SkPDF: when drawing stroked path, draw using SVG rules for zero-length segments

The "zeroPath" and emptystroke GMs capture this issue.

This CL changes the following PDF GMs: emptystroke dashing4
lineclosepath dashing3 zeroPath linepath
complexclip3_complex complexclip3_simple roundrects
degeneratesegments filltypes strokerect pathfill
inverse_paths desk_chalkboard.skp

After this change, all PDF GMs look better (closer to 8888).
The dashing4, emptystroke, and zeroPath GMs still need a lot
of work to make them look right.

BUG=538726

Review URL: https://codereview.chromium.org/1374383004

1 files changed, 54 insertions, 0 deletions

diff --git a/gm/path_stroke_with_zero_length.cpp b/gm/path_stroke_with_zero_length.cpp
new file mode 100644
index 0000000000..dc52947da3
--- /dev/null
+++ b/gm/path_stroke_with_zero_length.cpp
@@ -0,0 +1,54 @@
+/*
+ * Copyright 2015 Google Inc.
+ *
+ * Use of this source code is governed by a BSD-style license that can be
+ * found in the LICENSE file.
+ */
+
+#include "SkPath.h"
+#include "SkStream.h"
+#include "gm.h"
+
+// Test how short paths are stroked with various caps
+DEF_SIMPLE_GM(path_stroke_with_zero_length, canvas, 240, 120) {
+    SkPath paths[5];
+    paths[0].moveTo(30.0f, 0);  // single line segment
+    paths[0].rLineTo(30.0f, 0);
+
+    paths[1].moveTo(90.0f, 0);  // single line segment with close
+    paths[1].rLineTo(30.0f, 0);
+    paths[1].close();
+
+    paths[2].moveTo(150.0f, 0);  // zero-length line
+    paths[2].rLineTo(0, 0);
+
+    paths[3].moveTo(180.0f, 0);  // zero-length line with close
+    paths[3].rLineTo(0, 0);
+    paths[3].close();
+
+    paths[4].moveTo(210.0f, 0);  // close only, no line
+    paths[4].close();
+
+    auto drawPaths = [&](const SkPaint& paint) {
+        canvas->translate(0, 30.0f);
+        for (const SkPath& path : paths) {
+            canvas->drawPath(path, paint);
+        }
+    };
+    
+    SkAutoCanvasRestore autoCanvasRestore(canvas, true);
+
+    SkPaint butt;
+    butt.setStyle(SkPaint::kStroke_Style);
+    butt.setStrokeWidth(20.0f);
+    butt.setStrokeCap(SkPaint::kButt_Cap);
+    drawPaths(butt);
+
+    SkPaint round(butt);
+    round.setStrokeCap(SkPaint::kRound_Cap);
+    drawPaths(round);
+
+    SkPaint square(butt);
+    square.setStrokeCap(SkPaint::kSquare_Cap);
+    drawPaths(square);
+}