Bug 1704631 - Expand the size for `background-attachmend: fixed` image. r=botond,tnikkel,geckoview-reviewers,owlish

Differential Revision: https://phabricator.services.mozilla.com/D169001

layout/painting/nsCSSRendering.cpp

@@ -2787,6 +2787,15 @@ nsRect nsCSSRendering::ComputeImageLayerPositioningArea(
           positionArea.Deflate(scrollbars);
         }
       }
+
+      // If we have the dynamic toolbar, we need to expand the image area to
+      // include the region under the dynamic toolbar, otherwise we will see a
+      // blank space under the toolbar.
+      if (aPresContext->IsRootContentDocumentCrossProcess() &&
+          aPresContext->HasDynamicToolbar()) {
+        positionArea.SizeTo(nsLayoutUtils::ExpandHeightForDynamicToolbar(
+            aPresContext, positionArea.Size()));
+      }
     }
   }
   *aAttachedToFrame = attachedToFrame;

mobile/android/geckoview/src/androidTest/java/org/mozilla/geckoview/test/DynamicToolbarTest.kt

@@ -636,7 +636,7 @@ class DynamicToolbarTest : BaseSessionTest() {
         val dynamicToolbarMaxHeight = SCREEN_HEIGHT / 2
         sessionRule.display?.run { setDynamicToolbarMaxHeight(dynamicToolbarMaxHeight) }
 
-        // Set active since setVerticalClipping call affects only for forground tab.
+        // Set active since setVerticalClipping call affects only for foreground tab.
         mainSession.setActive(true)
 
         mainSession.loadTestPath(BaseSessionTest.FIXED_BOTTOM)
@@ -662,4 +662,45 @@ class DynamicToolbarTest : BaseSessionTest() {
             assertScreenshotResult(it.capturePixels(), reference)
         }
     }
+
+    @WithDisplay(height = SCREEN_HEIGHT, width = SCREEN_WIDTH)
+    @Test
+    fun backgroundImageFixed() {
+        // Set ui.scrollbarFadeBeginDelay value to 0 to hide the overlayed scrollbars
+        // immediately.
+        sessionRule.setPrefsUntilTestEnd(
+            mapOf(
+                "ui.scrollbarFadeBeginDelay" to 0
+            )
+        )
+
+        val reference = getComparisonScreenshot(SCREEN_WIDTH, SCREEN_HEIGHT)
+
+        val dynamicToolbarMaxHeight = SCREEN_HEIGHT / 2
+        sessionRule.display?.run { setDynamicToolbarMaxHeight(dynamicToolbarMaxHeight) }
+
+        // Set active since setVerticalClipping call affects only for forground tab.
+        mainSession.setActive(true)
+
+        mainSession.loadTestPath(BaseSessionTest.TOUCH_ACTION_HTML_PATH)
+        mainSession.waitForPageStop()
+
+        // Specify the root background-color to match the reference image color and specify
+        // `background-attachment: fixed`.
+        mainSession.evaluateJS("document.documentElement.style.background = 'linear-gradient(green, green) fixed'")
+
+        // Make the root element scrollable.
+        mainSession.evaluateJS("document.documentElement.style.height = '100vh'")
+
+        mainSession.flushApzRepaints()
+
+        // Simulate the dynamic toolbar being hidden by the scroll
+        sessionRule.display?.run { setVerticalClipping(-dynamicToolbarMaxHeight) }
+
+        mainSession.flushApzRepaints()
+
+        sessionRule.display?.let {
+            assertScreenshotResult(it.capturePixels(), reference)
+        }
+    }
 }