Bug 812899 part 2. Change the centering code in nsImageDocument to only try vertically centering via auto margins when we're not overflowing in the vertical direction, because if we _are_ overflowing that should cut off part of the image per spec. r=khuey

dom/html/ImageDocument.cpp

@@ -414,7 +414,11 @@ ImageDocument::RestoreImage()
   imageContent->UnsetAttr(kNameSpaceID_None, nsGkAtoms::height, true);
   
   if (ImageIsOverflowing()) {
-    SetModeClass(eOverflowing);
+    if (!mImageIsOverflowingVertically) {
+      SetModeClass(eOverflowingHorizontalOnly);
+    } else {
+      SetModeClass(eOverflowingVertical);
+    }
   }
   else {
     SetModeClass(eNone);
@@ -506,10 +510,16 @@ ImageDocument::SetModeClass(eModeClasses mode)
     classList->Remove(NS_LITERAL_STRING("shrinkToFit"), rv);
   }
 
-  if (mode == eOverflowing) {
-    classList->Add(NS_LITERAL_STRING("overflowing"), rv);
+  if (mode == eOverflowingVertical) {
+    classList->Add(NS_LITERAL_STRING("overflowingVertical"), rv);
   } else {
-    classList->Remove(NS_LITERAL_STRING("overflowing"), rv);
+    classList->Remove(NS_LITERAL_STRING("overflowingVertical"), rv);
+  }
+
+  if (mode == eOverflowingHorizontalOnly) {
+    classList->Add(NS_LITERAL_STRING("overflowingHorizontalOnly"), rv);
+  } else {
+    classList->Remove(NS_LITERAL_STRING("overflowingHorizontalOnly"), rv);
   }
 }
 
@@ -682,17 +692,26 @@ ImageDocument::CheckOverflowing(bool changeState)
   }
 
   bool imageWasOverflowing = ImageIsOverflowing();
+  bool imageWasOverflowingVertically = mImageIsOverflowingVertically;
   mImageIsOverflowingHorizontally = mImageWidth > mVisibleWidth;
   mImageIsOverflowingVertically = mImageHeight > mVisibleHeight;
   bool windowBecameBigEnough = imageWasOverflowing && !ImageIsOverflowing();
+  bool verticalOverflowChanged =
+    mImageIsOverflowingVertically != imageWasOverflowingVertically;
 
   if (changeState || mShouldResize || mFirstResize ||
-      windowBecameBigEnough) {
+      windowBecameBigEnough || verticalOverflowChanged) {
     if (ImageIsOverflowing() && (changeState || mShouldResize)) {
       ShrinkToFit();
     }
     else if (mImageIsResized || mFirstResize || windowBecameBigEnough) {
       RestoreImage();
+    } else if (!mImageIsResized && verticalOverflowChanged) {
+      if (mImageIsOverflowingVertically) {
+        SetModeClass(eOverflowingVertical);
+      } else {
+        SetModeClass(eOverflowingHorizontalOnly);
+      }
     }
   }
   mFirstResize = false;

dom/html/ImageDocument.h

@@ -101,7 +101,8 @@ protected:
   enum eModeClasses {
     eNone,
     eShrinkToFit,
-    eOverflowing
+    eOverflowingVertical, // And maybe horizontal too.
+    eOverflowingHorizontalOnly
   };
   void SetModeClass(eModeClasses mode);
 

dom/html/test/test_bug369370.html

@@ -88,8 +88,53 @@ https://bugzilla.mozilla.org/show_bug.cgi?id=369370
         is(kidDoc.body.scrollLeft,  0, "Checking scrollLeft");
         is(kidDoc.body.scrollTop,   0, "Checking scrollTop");
 
-        kidWin.close();
-        SimpleTest.finish();
+        // ========== test 5 ==========
+        // Click in the upper left to zoom in again
+        event = makeClickFor(25, 25);
+        img.dispatchEvent(event);
+        ok(true, "----- click 5 -----");
+        is(img.width,  800, "image width");
+        is(img.height, 600, "image height");
+        is(kidDoc.body.scrollLeft,  0, "Checking scrollLeft");
+        is(kidDoc.body.scrollTop,   0, "Checking scrollTop");
+        is(img.getBoundingClientRect().top, 0, "Image is in view vertically");
+
+        // ========== test 6 ==========
+        // Now try resizing the window so the image fits vertically.
+        function test6() {
+          kidWin.addEventListener("resize", function resizeListener() {
+            kidWin.removeEventListener("resize", resizeListener);
+            // Give the image document time to respond
+            SimpleTest.executeSoon(function() {
+              is(img.height, 600, "image height");
+              is(img.getBoundingClientRect().top, 25, "Image is vertically centered");
+              test7();
+            });
+          });
+
+          var decorationSize = kidWin.outerHeight - kidWin.innerHeight;
+          kidWin.resizeTo(400, 600 + 50 + decorationSize);
+        }
+
+        // ========== test 7 ==========
+        // Now try resizing the window so the image no longer fits vertically.
+        function test7() {
+          kidWin.addEventListener("resize", function resizeListener() {
+            kidWin.removeEventListener("resize", resizeListener);
+            // Give the image document time to respond
+            SimpleTest.executeSoon(function() {
+              is(img.height, 600, "image height");
+              is(img.getBoundingClientRect().top, 0, "Image is at top again");
+              kidWin.close();
+              SimpleTest.finish();
+            });
+          });
+
+          var decorationSize = kidWin.outerHeight - kidWin.innerHeight;
+          kidWin.resizeTo(400, 300 + decorationSize);
+        }
+
+        test6();
     }
     var kidWin;
     var kidDoc;

layout/style/ImageDocument.css

@@ -9,7 +9,7 @@
 */
 
 @media not print {
-  .overflowing {
+  .overflowingVertical, .overflowingHorizontalOnly {
     cursor: zoom-out;
   }
 

layout/style/TopLevelImageDocument.css

@@ -23,6 +23,13 @@
     left: 0;
   }
 
+  img.overflowingVertical {
+    /* If we're overflowing vertically, we need to set margin-top to
+       0.  Otherwise we'll end up trying to vertically center, and end
+       up cutting off the top part of the image. */
+    margin-top: 0;
+  }
+
   .completeRotation {
     transition: transform 0.3s ease 0s;
   }