Introduce some util code for drawing vector assets.

ui/gfx/vector_icons.cc

+// Copyright 2015 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#include "ui/gfx/vector_icons.h"
+
+#include "ui/gfx/canvas.h"
+
+namespace gfx {
+
+namespace {
+
+const int kReferenceSizeDp = 48;
+
+enum CommandType {
+  MOVE_TO,
+  R_MOVE_TO,
+  LINE_TO,
+  R_LINE_TO,
+  H_LINE_TO,
+  R_H_LINE_TO,
+  V_LINE_TO,
+  R_V_LINE_TO,
+  R_CUBIC_TO,
+  CIRCLE,
+  CLOSE,
+  END
+};
+
+struct PathElement {
+  PathElement(CommandType value) : type(value) {}
+  PathElement(SkScalar value) : arg(value) {}
+
+  union {
+    CommandType type;
+    SkScalar arg;
+  };
+};

[sadrul, 2015/07/07 04:18:11]

Would it make sense for PathElement to have a bool (e.g. is_command) which gets
set in the constructors, and is DCHECK()ed below in PaintVectorIcon to make sure
we are specifying the right number of args for each type? Something like:

 for (i ...) {
   DCHECK(path_elements[i].is_command);
   switch (path_elements[i].type) {
     case X:
       DCHECK(!path_elements[i + 1].is_command);
       DCHECK(!path_elements[i + 2].is_command);
       ...
   }
 }

[Peter Kasting, 2015/07/07 04:55:17]

I think this adds too much boilerplate to the class and code for little gain. 
It's unlikely someone would get this wrong and not notice.

+
+const PathElement* GetPathForVectorIcon(VectorIconId id) {
+  switch (id) {
+    case VectorIconId::VECTOR_ICON_NONE:
+      NOTREACHED();
+      return nullptr;
+
+    case VectorIconId::CHECK_CIRCLE: {
+      static PathElement path[] = {
+        CIRCLE, 24, 24, 20,
+        MOVE_TO, 20, 34,
+        LINE_TO, 10, 24,
+        R_LINE_TO, 2.83f, -2.83f,
+        LINE_TO, 20, 28.34f,
+        R_LINE_TO, 15.17f, -15.17f,
+        LINE_TO, 38, 16,
+        LINE_TO, 20, 34,
+        END
+      };
+      return path;
+    }
+
+    case VectorIconId::PHOTO_CAMERA: {
+      static PathElement path[] = {
+        CIRCLE, 24, 24, 6.4f,
+        MOVE_TO, 18, 4,
+        R_LINE_TO, -3.66f, 4,
+        H_LINE_TO, 8,
+        R_CUBIC_TO, -2.21f, 0, -4, 1.79f, -4, 4,
+        R_V_LINE_TO, 24,
+        R_CUBIC_TO, 0, 2.21f, 1.79f, 4, 4, 4,
+        R_H_LINE_TO, 32,
+        R_CUBIC_TO, 2.21f, 0, 4, -1.79f, 4, -4,
+        V_LINE_TO, 12,
+        R_CUBIC_TO, 0, -2.21f, -1.79f, -4, -4, -4,
+        R_H_LINE_TO, -6.34f,
+        LINE_TO, 30, 4,
+        H_LINE_TO, 18,
+        CLOSE,
+        CIRCLE, 24, 24, 10,
+        END
+      };
+      return path;
+    }
+  }
+}
+
+}  // namespace
+
+void PaintVectorIcon(Canvas* canvas,
+                     VectorIconId id,
+                     size_t dp_size,
+                     SkColor color) {
+  DCHECK(VectorIconId::VECTOR_ICON_NONE != id);
+  const PathElement* path_elements = GetPathForVectorIcon(id);
+  SkPath path;
+  path.setFillType(SkPath::kEvenOdd_FillType);
+  if (dp_size != kReferenceSizeDp) {
+    SkScalar scale = SkIntToScalar(dp_size) / SkIntToScalar(kReferenceSizeDp);
+    canvas->sk_canvas()->scale(scale, scale);
+  }
+
+  for (size_t i = 0; path_elements[i].type != END;) {
+    switch (path_elements[i++].type) {
+      case MOVE_TO: {
+        SkScalar x = path_elements[i++].arg;
+        SkScalar y = path_elements[i++].arg;
+        path.moveTo(x, y);
+        break;
+      }
+
+      case R_MOVE_TO: {
+        SkScalar x = path_elements[i++].arg;
+        SkScalar y = path_elements[i++].arg;
+        path.rMoveTo(x, y);
+        break;
+      }
+
+      case LINE_TO: {
+        SkScalar x = path_elements[i++].arg;
+        SkScalar y = path_elements[i++].arg;
+        path.lineTo(x, y);
+        break;
+      }
+
+      case R_LINE_TO: {
+        SkScalar x = path_elements[i++].arg;
+        SkScalar y = path_elements[i++].arg;
+        path.rLineTo(x, y);
+        break;
+      }
+
+      case H_LINE_TO: {
+        SkPoint last_point;
+        path.getLastPt(&last_point);

[sadrul, 2015/07/07 04:18:11]

DCHECK that this returns true?

[Evan Stade, 2015/07/07 16:47:50]

It needn't return true. You could start a path with H_LINE_TO and expect it to
make a horizontal line from (0, 0) to some point.

+        SkScalar x = path_elements[i++].arg;
+        path.lineTo(x, last_point.fY);
+        break;
+      }
+
+      case R_H_LINE_TO: {
+        SkScalar x = path_elements[i++].arg;
+        path.rLineTo(x, 0);
+        break;
+      }
+
+      case V_LINE_TO: {
+        SkPoint last_point;
+        path.getLastPt(&last_point);

[sadrul, 2015/07/07 04:18:11]

ditto

+        SkScalar y = path_elements[i++].arg;
+        path.lineTo(last_point.fX, y);
+        break;
+      }
+
+      case R_V_LINE_TO: {
+        SkScalar y = path_elements[i++].arg;
+        path.rLineTo(0, y);
+        break;
+      }
+
+      case R_CUBIC_TO: {
+        SkScalar x1 = path_elements[i++].arg;
+        SkScalar y1 = path_elements[i++].arg;
+        SkScalar x2 = path_elements[i++].arg;
+        SkScalar y2 = path_elements[i++].arg;
+        SkScalar x3 = path_elements[i++].arg;
+        SkScalar y3 = path_elements[i++].arg;
+        path.rCubicTo(x1, y1, x2, y2, x3, y3);
+        break;
+      }
+
+      case CLOSE: {
+        path.close();
+        break;
+      }
+
+      case CIRCLE: {
+        SkScalar x = path_elements[i++].arg;
+        SkScalar y = path_elements[i++].arg;
+        SkScalar r = path_elements[i++].arg;
+        path.addCircle(x, y, r);
+        break;
+      }
+
+      case END:
+        NOTREACHED();
+        break;
+    }
+  }
+
+  SkPaint paint;
+  paint.setStyle(SkPaint::kFill_Style);
+  paint.setAntiAlias(true);
+  paint.setColor(color);
+  canvas->DrawPath(path, paint);
+}
+
+}  // namespace gfx