Bug 1844992 - refactor GetSubStringLength r=emilio

Differential Revision: https://phabricator.services.mozilla.com/D184410

dom/svg/SVGTextContentElement.cpp

@@ -132,7 +132,20 @@ float SVGTextContentElement::GetSubStringLength(uint32_t charnum,
   SVGTextFrame* textFrame = GetSVGTextFrameForNonLayoutDependentQuery();
   if (!textFrame) return 0.0f;
 
-  return textFrame->GetSubStringLength(this, charnum, nchars, rv);
+  if (!textFrame->RequiresSlowFallbackForSubStringLength()) {
+    return textFrame->GetSubStringLengthFastPath(this, charnum, nchars, rv);
+  }
+  // We need to make sure that we've been reflowed before using the slow
+  // fallback path as it may affect glyph positioning. GetSVGTextFrame will do
+  // that for us.
+  // XXX perf: It may be possible to limit reflow to just calling ReflowSVG,
+  // but we would still need to resort to full reflow for percentage
+  // positioning attributes.  For now we just do a full reflow regardless
+  // since the cases that would cause us to be called are relatively uncommon.
+  textFrame = GetSVGTextFrame();
+  if (!textFrame) return 0.0f;
+
+  return textFrame->GetSubStringLengthSlowFallback(this, charnum, nchars, rv);
 }
 
 already_AddRefed<DOMSVGPoint> SVGTextContentElement::GetStartPositionOfChar(

layout/svg/SVGTextFrame.cpp

@@ -3509,34 +3509,43 @@ void SVGTextFrame::SelectSubString(nsIContent* aContent, uint32_t charnum,
 }
 
 /**
- * Implements the SVG DOM GetSubStringLength method for the specified
- * text content element.
+ * For some content we cannot (or currently cannot) compute the length
+ * without reflowing.  In those cases we need to fall back to using
+ * GetSubStringLengthSlowFallback.
+ *
+ * We fall back for textPath since we need glyph positioning in order to
+ * tell if any characters should be ignored due to having fallen off the
+ * end of the textPath.
+ *
+ * We fall back for bidi because GetTrimmedOffsets does not produce the
+ * correct results for bidi continuations when passed aPostReflow = false.
+ * XXX It may be possible to determine which continuations to trim from (and
+ * which sides), but currently we don't do that.  It would require us to
+ * identify the visual (rather than logical) start and end of the line, to
+ * avoid trimming at line-internal frame boundaries.  Maybe nsBidiPresUtils
+ * methods like GetFrameToRightOf and GetFrameToLeftOf would help?
+ *
  */
-float SVGTextFrame::GetSubStringLength(nsIContent* aContent, uint32_t charnum,
-                                       uint32_t nchars, ErrorResult& aRv) {
-  // For some content we cannot (or currently cannot) compute the length
-  // without reflowing.  In those cases we need to fall back to using
-  // GetSubStringLengthSlowFallback.
-  //
-  // We fall back for textPath since we need glyph positioning in order to
-  // tell if any characters should be ignored due to having fallen off the
-  // end of the textPath.
-  //
-  // We fall back for bidi because GetTrimmedOffsets does not produce the
-  // correct results for bidi continuations when passed aPostReflow = false.
-  // XXX It may be possible to determine which continuations to trim from (and
-  // which sides), but currently we don't do that.  It would require us to
-  // identify the visual (rather than logical) start and end of the line, to
-  // avoid trimming at line-internal frame boundaries.  Maybe nsBidiPresUtils
-  // methods like GetFrameToRightOf and GetFrameToLeftOf would help?
-  //
+bool SVGTextFrame::RequiresSlowFallbackForSubStringLength() {
   TextFrameIterator frameIter(this);
   for (nsTextFrame* frame = frameIter.Current(); frame;
        frame = frameIter.Next()) {
     if (frameIter.TextPathFrame() || frame->GetNextContinuation()) {
-      return GetSubStringLengthSlowFallback(aContent, charnum, nchars, aRv);
+      return true;
     }
   }
+  return false;
+}
+
+/**
+ * Implements the SVG DOM GetSubStringLength method for the specified
+ * text content element.
+ */
+float SVGTextFrame::GetSubStringLengthFastPath(nsIContent* aContent,
+                                               uint32_t charnum,
+                                               uint32_t nchars,
+                                               ErrorResult& aRv) {
+  MOZ_ASSERT(!RequiresSlowFallbackForSubStringLength());
 
   // We only need our text correspondence to be up to date (no need to call
   // UpdateGlyphPositioning).
@@ -3630,15 +3639,6 @@ float SVGTextFrame::GetSubStringLengthSlowFallback(nsIContent* aContent,
                                                    uint32_t charnum,
                                                    uint32_t nchars,
                                                    ErrorResult& aRv) {
-  // We need to make sure that we've been reflowed before updating the glyph
-  // positioning.
-  // XXX perf: It may be possible to limit reflow to just calling ReflowSVG,
-  // but we would still need to resort to full reflow for percentage
-  // positioning attributes.  For now we just do a full reflow regardless since
-  // the cases that would cause us to be called are relatively uncommon.
-  RefPtr<mozilla::PresShell> presShell = PresShell();
-  presShell->FlushPendingNotifications(FlushType::Layout);
-
   UpdateGlyphPositioning();
 
   // Convert charnum/nchars from addressable characters relative to

layout/svg/SVGTextFrame.h

@@ -241,9 +241,20 @@ class SVGTextFrame final : public SVGDisplayContainerFrame {
                                                    uint32_t charnum,
                                                    uint32_t nchars,
                                                    ErrorResult& aRv);
-  MOZ_CAN_RUN_SCRIPT
-  float GetSubStringLength(nsIContent* aContent, uint32_t charnum,
-                           uint32_t nchars, ErrorResult& aRv);
+  bool RequiresSlowFallbackForSubStringLength();
+  float GetSubStringLengthFastPath(nsIContent* aContent, uint32_t charnum,
+                                   uint32_t nchars, ErrorResult& aRv);
+  /**
+   * This fallback version of GetSubStringLength takes
+   * into account glyph positioning and requires us to have flushed layout
+   * before calling it. As per the SVG 2 spec, typically glyph
+   * positioning does not affect the results of getSubStringLength, but one
+   * exception is text in a textPath where we need to ignore characters that
+   * fall off the end of the textPath path.
+   */
+  float GetSubStringLengthSlowFallback(nsIContent* aContent, uint32_t charnum,
+                                       uint32_t nchars, ErrorResult& aRv);
+
   int32_t GetCharNumAtPosition(nsIContent* aContent,
                                const dom::DOMPointInit& aPoint);
 
@@ -405,17 +416,6 @@ class SVGTextFrame final : public SVGDisplayContainerFrame {
    */
   void DoGlyphPositioning();
 
-  /**
-   * This fallback version of GetSubStringLength that flushes layout and takes
-   * into account glyph positioning.  As per the SVG 2 spec, typically glyph
-   * positioning does not affect the results of getSubStringLength, but one
-   * exception is text in a textPath where we need to ignore characters that
-   * fall off the end of the textPath path.
-   */
-  MOZ_CAN_RUN_SCRIPT
-  float GetSubStringLengthSlowFallback(nsIContent* aContent, uint32_t charnum,
-                                       uint32_t nchars, ErrorResult& aRv);
-
   /**
    * Converts the specified index into mPositions to an addressable
    * character index (as can be used with the SVG DOM text methods)