Bug 876129 - Part 2: Prefer to look at <body> instead of <html> when determining whether the background color of a page is dark or not; r=roc

This seems to be a slightly better heuristic to follow the CSS Rendering code in all cases, since the background color for the body element often overrides that of the html element. --HG-- extra : rebase_source : ef4ac31003d75fb0fe17b493d7267ba3306e77bf
2013-05-30 22:23:49 -04:00 · 2013-05-30 22:23:49 -04:00 · d0eb61c94b
--- a/widget/xpwidgets/nsNativeTheme.cpp
+++ b/widget/xpwidgets/nsNativeTheme.cpp
@ -25,6 +25,8 @@
 #include "nsRangeFrame.h"
 #include "nsCSSRendering.h"
 #include "mozilla/dom/Element.h"
+#include "mozilla/dom/HTMLBodyElement.h"
+#include "nsIDocumentInlines.h"
 #include <algorithm>

 nsNativeTheme::nsNativeTheme()
@ -679,6 +681,21 @@ nsNativeTheme::IsRangeHorizontal(nsIFrame* aFrame)
  return static_cast<nsRangeFrame*>(rangeFrame)->IsHorizontal();
 }

+static nsIFrame*
+GetBodyFrame(nsIFrame* aCanvasFrame)
+{
+  nsIContent* content = aCanvasFrame->GetContent();
+  if (!content) {
+    return nullptr;
+  }
+  nsIDocument* document = content->OwnerDoc();
+  nsIContent* body = document->GetBodyElement();
+  if (!body) {
+    return nullptr;
+  }
+  return body->GetPrimaryFrame();
+}
+
 bool
 nsNativeTheme::IsDarkBackground(nsIFrame* aFrame)
 {
@ -691,6 +708,16 @@ nsNativeTheme::IsDarkBackground(nsIFrame* aFrame)
    return false;

  nsIFrame* frame = scrollFrame->GetScrolledFrame();
+  if (nsCSSRendering::IsCanvasFrame(frame)) {
+    // For canvas frames, prefer to look at the body first, because the body
+    // background color is most likely what will be visible as the background
+    // color of the page, even if the html element has a different background
+    // color which prevents that of the body frame to propagate to the viewport.
+    nsIFrame* bodyFrame = GetBodyFrame(frame);
+    if (bodyFrame) {
+      frame = bodyFrame;
+    }
+  }
  nsStyleContext* bgSC = nullptr;
  if (!nsCSSRendering::FindBackground(frame, &bgSC) ||
      bgSC->StyleBackground()->IsTransparent()) {