Preventing touch events from registering when they occur outside the desktop image

remoting/android/java/src/org/chromium/chromoting/TouchInputHandler.java

 // Copyright 2013 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 package org.chromium.chromoting;
 
 import android.content.Context;
 import android.graphics.Matrix;
 import android.graphics.Point;
 import android.graphics.PointF;
@@ skipping 552 matching lines @@
 
         /** Called when the user taps the screen with one or more fingers. */
         @Override
         public boolean onTap(int pointerCount, float x, float y) {
             int button = mouseButtonFromPointerCount(pointerCount);
             if (button == InputStub.BUTTON_UNDEFINED) {
                 return false;
             }
 
             if (!mInputStrategy.isIndirectInputMode()) {
+                if (!mapScreenPointToImage(x, y)) {
+                    return false;
+                }
                 moveCursorToScreenPoint(x, y);
             }
 
             if (mInputStrategy.onTap(button)) {
                 Point pos;
                 synchronized (mRenderData) {
                     pos = mRenderData.getCursorPosition();
                 }
                 mViewer.showInputFeedback(mInputStrategy.getShortPressFeedbackType(), pos);
             }
             return true;
         }
 
         /** Called when a long-press is triggered for one or more fingers. */
         @Override
         public void onLongPress(int pointerCount, float x, float y) {
             int button = mouseButtonFromPointerCount(pointerCount);
             if (button == InputStub.BUTTON_UNDEFINED) {
                 return;
             }
 
             if (!mInputStrategy.isIndirectInputMode()) {
+                if (!mapScreenPointToImage(x, y)) {
+                    return;
+                }
                 moveCursorToScreenPoint(x, y);
             }
 
             if (mInputStrategy.onPressAndHold(button)) {
                 Point pos;
                 synchronized (mRenderData) {
                     pos = mRenderData.getCursorPosition();
                 }
                 mViewer.showInputFeedback(mInputStrategy.getLongPressFeedbackType(), pos);
                 mSuppressFling = true;
                 mIsDragging = true;
             }
         }
 
         /** Maps the number of fingers in a tap or long-press gesture to a mouse-button. */
         private int mouseButtonFromPointerCount(int pointerCount) {
             switch (pointerCount) {
                 case 1:
                     return InputStub.BUTTON_LEFT;
                 case 2:
                     return InputStub.BUTTON_RIGHT;
                 case 3:
                     return InputStub.BUTTON_MIDDLE;
                 default:
                     return InputStub.BUTTON_UNDEFINED;
             }
         }
+
+        /** Verifies the given point maps to a valid location within the desktop image. */
+        private boolean mapScreenPointToImage(float screenX, float screenY) {

[Lambros, 2016/07/12 23:19:50]

Looks like we have this logic a few times in this file already. Maybe have this
function take a mutable PointF object to accept the transformed coords? Doesn't
have to block this CL from landing.

[joedow, 2016/07/13 00:04:50]

Ack.  I was thinking this kind of functionality may make sense to move in
RenderData (if it continues to exist with the refactoring).  Leaving for this CL
but will consider it in a future CL.

+            float[] mappedPoints = {screenX, screenY};
+            int imageWidth;
+            int imageHeight;
+            Matrix screenToImage = new Matrix();
+            synchronized (mRenderData) {
+                mRenderData.transform.invert(screenToImage);
+                imageWidth = mRenderData.imageWidth;
+                imageHeight = mRenderData.imageHeight;
+            }
+            screenToImage.mapPoints(mappedPoints);
+
+            return (mappedPoints[0] >= 0 && mappedPoints[0] <= imageWidth)

[Lambros, 2016/07/12 23:19:50]

Is it worth adding a little bit of slop margin here? If the user taps at the
extreme edge, it might be a bit frustrating for the tap to sometimes go through
and sometimes not?

[joedow, 2016/07/13 00:04:50]

I considered that, but this method is only used when the display is sufficiently
shrunk that the desktop image has a border.  If they are having difficulty
tapping an edge target (or any target really), I'd think it would be more
reliable for them to zoom in a bit.

+                    && (mappedPoints[1] >= 0 && mappedPoints[1] <= imageHeight);
+        }
     }
 }