Optimize single-segment Path::fastBoundingRect()

https://bugs.webkit.org/show_bug.cgi?id=290234
rdar://147623819

Reviewed by Cameron McCormack.

`PathStream::computeFastBoundingRect()` has some overhead we can remove if we just have
a single segment; the loop, and the call to `calculateEndPoint()`. So implement in
`Path::fastBoundingRect()` in a way that works for single segment paths.

* Source/WebCore/platform/graphics/Path.cpp:
(WebCore::Path::fastBoundingRect const):

Canonical link: https://commits.webkit.org/292543@main

Author: smfr

Source/WebCore/platform/graphics/Path.cpp

@@ -629,7 +629,7 @@ bool Path::hasSubpaths() const
 FloatRect Path::fastBoundingRect() const
 {
     if (auto* segment = asSingle())
-        return PathStream::computeFastBoundingRect(singleElementSpan(*segment));
+        return segment->fastBoundingRect();
 
     if (auto* impl = asImpl())
         return impl->fastBoundingRect();

Source/WebCore/platform/graphics/PathSegment.cpp

@@ -51,6 +51,22 @@ std::optional<FloatPoint> PathSegment::tryGetEndPointWithoutContext() const
     });
 }
 
+FloatRect PathSegment::fastBoundingRect() const
+{
+    FloatPoint currentPoint;
+    FloatPoint lastMoveToPoint;
+
+    auto boundingRect = FloatRect::smallestRect();
+    extendFastBoundingRect(currentPoint, lastMoveToPoint, boundingRect);
+
+    if (boundingRect.isSmallest()) {
+        currentPoint = calculateEndPoint(currentPoint, lastMoveToPoint);
+        boundingRect.extend(currentPoint);
+    }
+
+    return boundingRect;
+}
+
 void PathSegment::extendFastBoundingRect(const FloatPoint& currentPoint, const FloatPoint& lastMoveToPoint, FloatRect& boundingRect) const
 {
     WTF::switchOn(m_data, [&](auto& data) {

Source/WebCore/platform/graphics/PathSegment.h

@@ -66,6 +66,8 @@ class PathSegment {
 
     FloatPoint calculateEndPoint(const FloatPoint& currentPoint, FloatPoint& lastMoveToPoint) const;
     std::optional<FloatPoint> tryGetEndPointWithoutContext() const;
+
+    FloatRect fastBoundingRect() const;
     void extendFastBoundingRect(const FloatPoint& currentPoint, const FloatPoint& lastMoveToPoint, FloatRect& boundingRect) const;
     void extendBoundingRect(const FloatPoint& currentPoint, const FloatPoint& lastMoveToPoint, FloatRect& boundingRect) const;