Implement canvas focus ring methods.

Source/core/html/canvas/CanvasRenderingContext2D.cpp

Index: Source/core/html/canvas/CanvasRenderingContext2D.cpp
diff --git a/Source/core/html/canvas/CanvasRenderingContext2D.cpp b/Source/core/html/canvas/CanvasRenderingContext2D.cpp
index 16248369b57dc383f2cd44936d60dd3f857e28a3..162d55685b8c9a754ba09eaeb05ff51ce4754469 100644
--- a/Source/core/html/canvas/CanvasRenderingContext2D.cpp
+++ b/Source/core/html/canvas/CanvasRenderingContext2D.cpp
@@ -34,6 +34,7 @@
 #include "core/html/canvas/CanvasRenderingContext2D.h"
 
 #include "CSSPropertyNames.h"
+#include "core/accessibility/AXObjectCache.h"
 #include "core/css/CSSFontSelector.h"
 #include "core/css/CSSParser.h"
 #include "core/css/StylePropertySet.h"
@@ -60,6 +61,7 @@
 #include "core/platform/graphics/TextRun.h"
 #include "core/platform/graphics/transforms/AffineTransform.h"
 #include "core/rendering/RenderLayer.h"
+#include "core/rendering/RenderTheme.h"
 #include "weborigin/SecurityOrigin.h"
 
 #include "wtf/CheckedArithmetic.h"
@@ -2337,4 +2339,56 @@ PassRefPtr<Canvas2DContextAttributes> CanvasRenderingContext2D::getContextAttrib
     return attributes.release();
 }
 
+void CanvasRenderingContext2D::drawSystemFocusRing(Element* element)
+{
+    drawFocusRing(m_path, element, false);
+}
+
+bool CanvasRenderingContext2D::drawCustomFocusRing(Element* element)
+{
+    drawFocusRing(m_path, element, true);
+    // Blink doesn't draw a custom focus ring; we always return false to inform the web app it should draw it.
+    return false;
+}
+
+void CanvasRenderingContext2D::drawFocusRing(const Path& path, Element* element, bool custom)
+{
+    GraphicsContext* c = drawingContext();
+    if (!c)
+        return;
+    if (!state().m_invertibleCTM)
+        return;
+    if (path.isEmpty())
+        return;
+    FloatRect boundingRect = path.boundingRect();
+
+    // If accessibility is enabled, associate this bounding box with the element.
+    if (AXObjectCache* axObjectCache = element->document()->existingAXObjectCache()) {
+        if (AccessibilityObject* obj = axObjectCache->getOrCreate(element)) {
+            IntRect canvasRect = canvas()->renderer()->absoluteBoundingBoxRect();
+            LayoutRect rect = LayoutRect(boundingRect);
+            rect.moveBy(canvasRect.location());
+            obj->setElementRect(rect);
+        }
+    }
+
+    // Only draw if the element is focused and if the function called wasn't drawCustomFocusRing.
+    if (custom || !element->focused())
+        return;
+
+    c->save();
+    c->setAlpha(1.0);
+    c->clearShadow();
+    c->setCompositeOperation(CompositeSourceOver, BlendModeNormal);
+
+    RefPtr<RenderStyle> style(RenderStyle::createDefaultStyle());
+    Color focusRingColor = RenderTheme::focusRingColor();
+    Vector<IntRect> rects;
+    rects.append(pixelSnappedIntRect(LayoutRect(boundingRect)));
+    c->drawFocusRing(rects, style->outlineWidth(), style->outlineOffset(), focusRingColor);

[jbroman, 2013/07/29 17:25:08]

Why not draw the path itself? GraphicsContext::drawFocusRing can take a path,
and the spec seems to suggest that is the correct behaviour.

If you'd like to close the path, there's Path::closeSubpath which should do the
trick (though it may make sense to leave that up to the content author). That's
how paths are closed in CanvasPathMethods::closePath, for instance.

[Rik, 2013/07/29 20:10:00]

I'm unsure this is true. The spec is confusing here by mentioning "around the
path" and "along the path"

[dmazzoni, 2013/07/29 21:44:21]

It's unclear to me too.

Since this is behind a flag, I don't really care too much, I
just want to throw it in front of a few web developers and see
if they find it confusing or not.

I currently changed it to just draw the path without closing it.
Let's see how that goes.

+
+    c->restore();
+    didDraw(boundingRect);
+}
+
 } // namespace WebCore