Add support for new canvas ellipse method.

Source/core/html/canvas/CanvasPathMethods.cpp

Index: Source/core/html/canvas/CanvasPathMethods.cpp
diff --git a/Source/core/html/canvas/CanvasPathMethods.cpp b/Source/core/html/canvas/CanvasPathMethods.cpp
index 0226af21d52095cce66cdd6c9ba0d00b2dd05aa8..7d4cd1c3db98eb98f5bf2fc6789af64320602f44 100644
--- a/Source/core/html/canvas/CanvasPathMethods.cpp
+++ b/Source/core/html/canvas/CanvasPathMethods.cpp
@@ -130,37 +130,97 @@ void CanvasPathMethods::arcTo(float x1, float y1, float x2, float y2, float r, E
         m_path.addArcTo(p1, p2, r);
 }
 
-void CanvasPathMethods::arc(float x, float y, float r, float sa, float ea, bool anticlockwise, ExceptionCode& ec)
+static float adjustEndAngle(float startAngle, float endAngle, bool anticlockwise)
+{
+    // If 'startAngle' and 'endAngle' differ by more than 2Pi, just add a circle starting/ending at 'startAngle'.
+    if (anticlockwise && startAngle - endAngle >= 2 * piFloat)
+        return startAngle - 2 * piFloat;
+    if (!anticlockwise && endAngle - startAngle >= 2 * piFloat)
+        return startAngle + 2 * piFloat;
+    return endAngle;
+}
+
+void CanvasPathMethods::arc(float x, float y, float radius, float startAngle, float endAngle, bool anticlockwise, ExceptionCode& ec)
 {
     ec = 0;
-    if (!std::isfinite(x) || !std::isfinite(y) || !std::isfinite(r) || !std::isfinite(sa) || !std::isfinite(ea))
+    if (!std::isfinite(x) || !std::isfinite(y) || !std::isfinite(radius) || !std::isfinite(startAngle) || !std::isfinite(endAngle))
         return;
 
-    if (r < 0) {
+    if (radius < 0) {
         ec = INDEX_SIZE_ERR;
         return;
     }
 
-    if (!r || sa == ea) {
+    if (!radius || startAngle == endAngle) {
         // The arc is empty but we still need to draw the connecting line.
-        lineTo(x + r * cosf(sa), y + r * sinf(sa));
+        lineTo(x + radius * cosf(startAngle), y + radius * sinf(startAngle));
         return;
     }
 
     if (!isTransformInvertible())
         return;
 
-    // If 'sa' and 'ea' differ by more than 2Pi, just add a circle starting/ending at 'sa'.
-    if (anticlockwise && sa - ea >= 2 * piFloat) {
-        m_path.addArc(FloatPoint(x, y), r, sa, sa - 2 * piFloat, anticlockwise);
+    float adjustedEndAngle = adjustEndAngle(startAngle, endAngle, anticlockwise);
+    m_path.addArc(FloatPoint(x, y), radius, startAngle, adjustedEndAngle, anticlockwise);
+}
+
+static void degenerateEllipse(CanvasPathMethods* path, float x, float y, float radiusX, float radiusY, float rotation, float startAngle, float endAngle, bool anticlockwise)
+{
+    ASSERT((radiusX || radiusY) && startAngle != endAngle);
+    float sweep = endAngle - startAngle;
+    if (anticlockwise)
+        sweep = startAngle - endAngle;
+
+    if (sweep < 0)
+        sweep = std::fmod(-sweep,  piFloat * 2);
+
+    if (sweep <= piFloat * 0.5) {
+        path->lineTo(x + radiusX * cosf(endAngle + rotation), y + radiusY * sinf(endAngle + rotation));

[alph, 2013/07/09 16:21:23]

Here's a counter example:
rotation = x = y = 0;
startAngle = -pi/4;
endAngle = pi/4;
radiusX = 100;
radiusY = 0;
The line should go from (sqrt(2)/2*100; 0) to (100; 0).
You draw just a single point of (sqrt(2)/2*100; 0).

+    } else if (sweep <= piFloat) {
+        path->lineTo(x + radiusX * cosf(piFloat * 0.5), y + radiusY * sinf(piFloat * 0.5));
+        path->lineTo(x + radiusX * cosf(endAngle + rotation), y + radiusY * sinf(endAngle + rotation));
+    } else if (sweep <= piFloat * 1.5) {
+        path->lineTo(x + radiusX * cosf(piFloat * 0.5), y + radiusY * sinf(piFloat * 0.5));
+        path->lineTo(x + radiusX * cosf(piFloat), y + radiusY * sinf(piFloat));
+        path->lineTo(x + radiusX * cosf(endAngle + rotation), y + radiusY * sinf(endAngle + rotation));
+    } else if (sweep <= piFloat * 2) {
+        path->lineTo(x + radiusX * cosf(piFloat * 0.5), y + radiusY * sinf(piFloat * 0.5));
+        path->lineTo(x + radiusX * cosf(piFloat), y + radiusY * sinf(piFloat));
+        path->lineTo(x + radiusX * cosf(piFloat * 1.5), y + radiusY * sinf(piFloat * 1.5));
+        path->lineTo(x + radiusX * cosf(endAngle + rotation), y + radiusY * sinf(endAngle + rotation));
+    } else { //  sweep > piFloat * 2
+        path->lineTo(x + radiusX * cosf(piFloat * 0.5), y + radiusY * sinf(piFloat * 0.5));
+        path->lineTo(x + radiusX * cosf(piFloat), y + radiusY * sinf(piFloat));
+        path->lineTo(x + radiusX * cosf(piFloat * 1.5), y + radiusY * sinf(piFloat * 1.5));
+        path->lineTo(x + radiusX * cosf(piFloat * 2), y + radiusY * sinf(piFloat * 2));
+        path->lineTo(x + radiusX * cosf(endAngle + rotation), y + radiusY * sinf(endAngle + rotation));
+    }
+}
+
+void CanvasPathMethods::ellipse(float x, float y, float radiusX, float radiusY, float rotation, float startAngle, float endAngle, bool anticlockwise, ExceptionCode& ec)
+{
+    ec = 0;
+    if (!std::isfinite(x) || !std::isfinite(y) || !std::isfinite(radiusX) || !std::isfinite(radiusY) || !std::isfinite(rotation) || !std::isfinite(startAngle) || !std::isfinite(endAngle))
+        return;
+
+    if (radiusX < 0 || radiusY < 0) {
+        ec = INDEX_SIZE_ERR;
         return;
     }
-    if (!anticlockwise && ea - sa >= 2 * piFloat) {
-        m_path.addArc(FloatPoint(x, y), r, sa, sa + 2 * piFloat, anticlockwise);
+
+    if (!radiusX || !radiusY || startAngle == endAngle) {
+        // The ellipse is empty but we still need to draw the connecting line to start point.
+        lineTo(x + radiusX * cosf(startAngle + rotation), y + radiusY * sinf(startAngle + rotation));

[alph, 2013/07/09 16:21:23]

It still does not take into account axes rotation. How about something like
this:
float cos, sin;
sincosf(startAngle, &sin, &cos);
float x1 = radiusX * cos;
float y1 = radiusY * sin;
sincosf(rotation, &sin, &cos);
float x2 = x1 * cos - y1 * sin;
float y2 = x1 * sin + y1 * cos;
lineTo(x + x2, y + y2);

+        if ((radiusX || radiusY) && startAngle != endAngle)
+            degenerateEllipse(this, x, y, radiusX, radiusY, rotation, startAngle, endAngle, anticlockwise);

[dshwang, 2013/07/09 15:48:02]

@alph yes, you are right. I understand what you say.

How about this implementation?

Or if we want simpler implementation with losing some precision, below solution
can work.
Replace below code to degenerateEllipse(...)
if (!radiusX)
    radiusX = 0.00001;
if (!radiusY)
    radiusY = 0.00001;

Which do you prefer?

[alph, 2013/07/09 16:21:23]

degenerateEllipse already looks scary to me despite it still doesn't take into
account axes rotation. I don't like scary code as bugs might hide in it. ;-)

         return;
     }
 
-    m_path.addArc(FloatPoint(x, y), r, sa, ea, anticlockwise);
+    if (!isTransformInvertible())
+        return;
+
+    float adjustedEndAngle = adjustEndAngle(startAngle, endAngle, anticlockwise);
+    m_path.addEllipse(FloatPoint(x, y), radiusX, radiusY, rotation, startAngle, adjustedEndAngle, anticlockwise);
 }
 
 void CanvasPathMethods::rect(float x, float y, float width, float height)