Bug 1665064 - Honor print background image settings on WebRender too. r=kats,jwatt CLOSED TREE

We usually suppress background images in
nsCSSRendering::PaintStyleImageLayerWithSC, but that codepath isn't hit
by WebRender, so instead do it during display list building, the same
way we suppress background colors.

Differential Revision: https://phabricator.services.mozilla.com/D90278

layout/base/tests/chrome/printpreview_helper.xhtml

@@ -672,6 +672,16 @@ async function runTest25() {
 
 async function runTest26() {
   await compareFiles("printpreview_downloadable_font_in_iframe.html", "printpreview_downloadable_font_in_iframe_ref.html");
+  requestAnimationFrame(() => setTimeout(runTest27));
+}
+
+async function runTest27() {
+  await compareFiles("data:text/html,<style>:root { background-color: red; background-image: linear-gradient(red, red) }</style>", "data:text/html,", {
+    settings: {
+      printBGColors: false,
+      printBGImages: false,
+    }
+  });
   finish();
 }
 

layout/generic/nsCanvasFrame.cpp

@@ -515,15 +515,23 @@ void nsCanvasFrame::BuildDisplayList(nsDisplayListBuilder* aBuilder,
     bool needBlendContainer = false;
     nsDisplayListBuilder::AutoContainerASRTracker contASRTracker(aBuilder);
 
-    // In high-contrast-mode, we suppress background-image on the canvas frame
-    // (even when backplating), because users expect site backgrounds to conform
-    // to their HCM background color when a solid color is rendered, and some
-    // websites use solid-color images instead of an overwritable background
-    // color.
-    const bool suppressBackgroundImage =
-        !PresContext()->PrefSheetPrefs().mUseDocumentColors &&
-        StaticPrefs::
-            browser_display_suppress_canvas_background_image_on_forced_colors();
+    const bool suppressBackgroundImage = [&] {
+      // Handle print settings.
+      if (!ComputeShouldPaintBackground().mImage) {
+        return true;
+      }
+      // In high-contrast-mode, we suppress background-image on the canvas frame
+      // (even when backplating), because users expect site backgrounds to
+      // conform to their HCM background color when a solid color is rendered,
+      // and some websites use solid-color images instead of an overwritable
+      // background color.
+      if (!PresContext()->PrefSheetPrefs().mUseDocumentColors &&
+          StaticPrefs::
+              browser_display_suppress_canvas_background_image_on_forced_colors()) {
+        return true;
+      }
+      return false;
+    }();
 
     // Create separate items for each background layer.
     const nsStyleImageLayers& layers = bg->StyleBackground()->mImage;

layout/painting/nsDisplayList.cpp

@@ -3509,11 +3509,9 @@ bool nsDisplayBackgroundImage::AppendBackgroundItemsToTop(
   }
 
   bool drawBackgroundColor = false;
-  // Dummy initialisation to keep Valgrind/Memcheck happy.
-  // See bug 1122375 comment 1.
+  bool drawBackgroundImage = false;
   nscolor color = NS_RGBA(0, 0, 0, 0);
   if (!nsCSSRendering::IsCanvasFrame(aFrame) && bg) {
-    bool drawBackgroundImage;
     color = nsCSSRendering::DetermineBackgroundColor(
         presContext, bgSC, aFrame, drawBackgroundImage, drawBackgroundColor);
   }
@@ -3593,7 +3591,7 @@ bool nsDisplayBackgroundImage::AppendBackgroundItemsToTop(
     return true;
   }
 
-  if (!bg) {
+  if (!bg || !drawBackgroundImage) {
     aList->AppendToTop(&bgItemList);
     return false;
   }