Bug 716403 - Make the top of the page accessible with the toolbar visible. r=kats

This makes it possible to scroll to the top of the page with the toolbar visible
in Firefox for Android. It also causes JavaScript scrolling to position 0 to
expose the toolbar.

mobile/android/base/BrowserApp.java

@@ -179,9 +179,17 @@ abstract public class BrowserApp extends GeckoApp
     @Override
     public boolean onInterceptTouchEvent(View view, MotionEvent event) {
         int action = event.getActionMasked();
-
         int pointerCount = event.getPointerCount();
 
+        // Whenever there are no pointers left on the screen, tell the page
+        // to clamp the viewport on fixed layer margin changes. This lets the
+        // toolbar scrolling off the top of the page make the page scroll up
+        // if it'd cause the page to go into overscroll, but only when there
+        // are no pointers held down.
+        mLayerView.getLayerClient().setClampOnFixedLayerMarginsChange(
+            pointerCount == 0 || action == MotionEvent.ACTION_CANCEL ||
+            action == MotionEvent.ACTION_UP);
+
         View toolbarView = mBrowserToolbar.getLayout();
         if (action == MotionEvent.ACTION_DOWN ||
             action == MotionEvent.ACTION_POINTER_DOWN) {

mobile/android/base/gfx/GeckoLayerClient.java

@@ -91,6 +91,8 @@ public class GeckoLayerClient implements LayerView.Listener, PanZoomTarget
     private final PanZoomController mPanZoomController;
     private LayerView mView;
 
+    private boolean mClampOnMarginChange;
+
     public GeckoLayerClient(Context context, LayerView view, EventDispatcher eventDispatcher) {
         // we can fill these in with dummy values because they are always written
         // to before being read
@@ -105,6 +107,7 @@ public class GeckoLayerClient implements LayerView.Listener, PanZoomTarget
         mProgressiveUpdateDisplayPort = new DisplayPortMetrics();
         mLastProgressiveUpdateWasLowPrecision = false;
         mProgressiveUpdateWasInDanger = false;
+        mClampOnMarginChange = true;
 
         mForceRedraw = true;
         DisplayMetrics displayMetrics = context.getResources().getDisplayMetrics();
@@ -354,11 +357,21 @@ public class GeckoLayerClient implements LayerView.Listener, PanZoomTarget
      */
     public void setFixedLayerMargins(float left, float top, float right, float bottom) {
         ImmutableViewportMetrics oldMetrics = getViewportMetrics();
-        setViewportMetrics(oldMetrics.setFixedLayerMargins(left, top, right, bottom), false);
+        ImmutableViewportMetrics newMetrics = oldMetrics.setFixedLayerMargins(left, top, right, bottom);
+
+        if (mClampOnMarginChange) {
+            newMetrics = newMetrics.clampWithMargins();
+        }
+
+        setViewportMetrics(newMetrics, false);
 
         mView.requestRender();
     }
 
+    public void setClampOnFixedLayerMarginsChange(boolean aClamp) {
+        mClampOnMarginChange = aClamp;
+    }
+
     // This is called on the Gecko thread to determine if we're still interested
     // in the update of this display-port to continue. We can return true here
     // to abort the current update and continue with any subsequent ones. This
@@ -470,7 +483,15 @@ public class GeckoLayerClient implements LayerView.Listener, PanZoomTarget
             float pageLeft, float pageTop, float pageRight, float pageBottom,
             float cssPageLeft, float cssPageTop, float cssPageRight, float cssPageBottom) {
         synchronized (this) {
-            final ImmutableViewportMetrics newMetrics = getViewportMetrics()
+            ImmutableViewportMetrics currentMetrics = getViewportMetrics();
+
+            // If we're meant to be scrolled to the top, take into account any
+            // margin set on the pan zoom controller.
+            if (offsetY == 0) {
+                offsetY = -currentMetrics.fixedLayerMarginTop;
+            }
+
+            final ImmutableViewportMetrics newMetrics = currentMetrics
                 .setViewportOrigin(offsetX, offsetY)
                 .setZoomFactor(zoom)
                 .setPageRect(new RectF(pageLeft, pageTop, pageRight, pageBottom),
@@ -549,10 +570,20 @@ public class GeckoLayerClient implements LayerView.Listener, PanZoomTarget
         mCurrentViewTransform.x = mFrameMetrics.viewportRectLeft;
         mCurrentViewTransform.y = mFrameMetrics.viewportRectTop;
         mCurrentViewTransform.scale = mFrameMetrics.zoomFactor;
-        mCurrentViewTransform.fixedLayerMarginLeft = mFrameMetrics.fixedLayerMarginLeft;
-        mCurrentViewTransform.fixedLayerMarginTop = mFrameMetrics.fixedLayerMarginTop;
-        mCurrentViewTransform.fixedLayerMarginRight = mFrameMetrics.fixedLayerMarginRight;
-        mCurrentViewTransform.fixedLayerMarginBottom = mFrameMetrics.fixedLayerMarginBottom;
+
+        // Adjust the fixed layer margins so that overscroll subtracts from them.
+        mCurrentViewTransform.fixedLayerMarginLeft =
+            Math.max(0, mFrameMetrics.fixedLayerMarginLeft +
+                     Math.min(0, mFrameMetrics.viewportRectLeft - mFrameMetrics.pageRectLeft));
+        mCurrentViewTransform.fixedLayerMarginTop =
+            Math.max(0, mFrameMetrics.fixedLayerMarginTop +
+                     Math.min(0, mFrameMetrics.viewportRectTop - mFrameMetrics.pageRectTop));
+        mCurrentViewTransform.fixedLayerMarginRight =
+            Math.max(0, mFrameMetrics.fixedLayerMarginRight +
+                     Math.min(0, (mFrameMetrics.pageRectRight - mFrameMetrics.viewportRectRight)));
+        mCurrentViewTransform.fixedLayerMarginBottom =
+            Math.max(0, mFrameMetrics.fixedLayerMarginBottom +
+                     Math.min(0, (mFrameMetrics.pageRectBottom - mFrameMetrics.viewportRectBottom)));
 
         mRootLayer.setPositionAndResolution(x, y, x + width, y + height, resolution);
 

mobile/android/base/gfx/ImmutableViewportMetrics.java

@@ -237,19 +237,20 @@ public class ImmutableViewportMetrics {
     }
 
     /** Clamps the viewport to remain within the page rect. */
-    public ImmutableViewportMetrics clamp() {
+    private ImmutableViewportMetrics clamp(float marginLeft, float marginTop,
+                                           float marginRight, float marginBottom) {
         RectF newViewport = getViewport();
 
         // The viewport bounds ought to never exceed the page bounds.
-        if (newViewport.right > pageRectRight)
-            newViewport.offset(pageRectRight - newViewport.right, 0);
-        if (newViewport.left < pageRectLeft)
-            newViewport.offset(pageRectLeft - newViewport.left, 0);
+        if (newViewport.right > pageRectRight + marginRight)
+            newViewport.offset((pageRectRight + marginRight) - newViewport.right, 0);
+        if (newViewport.left < pageRectLeft - marginLeft)
+            newViewport.offset((pageRectLeft - marginLeft) - newViewport.left, 0);
 
-        if (newViewport.bottom > pageRectBottom)
-            newViewport.offset(0, pageRectBottom - newViewport.bottom);
-        if (newViewport.top < pageRectTop)
-            newViewport.offset(0, pageRectTop - newViewport.top);
+        if (newViewport.bottom > pageRectBottom + marginBottom)
+            newViewport.offset(0, (pageRectBottom + marginBottom) - newViewport.bottom);
+        if (newViewport.top < pageRectTop - marginTop)
+            newViewport.offset(0, (pageRectTop - marginTop) - newViewport.top);
 
         return new ImmutableViewportMetrics(
             pageRectLeft, pageRectTop, pageRectRight, pageRectBottom,
@@ -259,6 +260,15 @@ public class ImmutableViewportMetrics {
             zoomFactor);
     }
 
+    public ImmutableViewportMetrics clamp() {
+        return clamp(0, 0, 0, 0);
+    }
+
+    public ImmutableViewportMetrics clampWithMargins() {
+        return clamp(fixedLayerMarginLeft, fixedLayerMarginTop,
+                     fixedLayerMarginRight, fixedLayerMarginBottom);
+    }
+
     public boolean fuzzyEquals(ImmutableViewportMetrics other) {
         // Don't bother checking the pageRectXXX values because they are a product
         // of the cssPageRectXXX values and the zoomFactor, except with more rounding

mobile/android/base/gfx/JavaPanZoomController.java

@@ -857,7 +857,7 @@ class JavaPanZoomController
         }
 
         /* Now we pan to the right origin. */
-        viewportMetrics = viewportMetrics.clamp();
+        viewportMetrics = viewportMetrics.clampWithMargins();
 
         return viewportMetrics;
     }
@@ -869,9 +869,15 @@ class JavaPanZoomController
         @Override
         protected float getViewportLength() { return getMetrics().getWidth(); }
         @Override
-        protected float getPageStart() { return getMetrics().pageRectLeft; }
+        protected float getPageStart() {
+            ImmutableViewportMetrics metrics = getMetrics();
+            return metrics.pageRectLeft - metrics.fixedLayerMarginLeft;
+        }
         @Override
-        protected float getPageLength() { return getMetrics().getPageWidth(); }
+        protected float getPageLength() {
+            ImmutableViewportMetrics metrics = getMetrics();
+            return metrics.getPageWidth() + metrics.fixedLayerMarginLeft + metrics.fixedLayerMarginRight;
+        }
     }
 
     private class AxisY extends Axis {
@@ -881,9 +887,15 @@ class JavaPanZoomController
         @Override
         protected float getViewportLength() { return getMetrics().getHeight(); }
         @Override
-        protected float getPageStart() { return getMetrics().pageRectTop; }
+        protected float getPageStart() {
+            ImmutableViewportMetrics metrics = getMetrics();
+            return metrics.pageRectTop - metrics.fixedLayerMarginTop;
+        }
         @Override
-        protected float getPageLength() { return getMetrics().getPageHeight(); }
+        protected float getPageLength() {
+            ImmutableViewportMetrics metrics = getMetrics();
+            return metrics.getPageHeight() + metrics.fixedLayerMarginTop + metrics.fixedLayerMarginBottom;
+        }
     }
 
     /*