Improved Pinch-Zoom for PDF.

chrome/browser/resources/pdf/viewport.js

Index: chrome/browser/resources/pdf/viewport.js
diff --git a/chrome/browser/resources/pdf/viewport.js b/chrome/browser/resources/pdf/viewport.js
index 18fb6c2ad403f4c8a49956f43a37bc776eaece6e..7c3ccca03bdb45b4422bcf5786234abee4fcb34c 100644
--- a/chrome/browser/resources/pdf/viewport.js
+++ b/chrome/browser/resources/pdf/viewport.js
@@ -15,6 +15,36 @@ function getIntersectionHeight(rect1, rect2) {
 }
 
 /**
+ * Makes sure that the scale level doesn't get out of the limits.
+ * @param {number} scale The new scale level.
+ * @return {number} The scale clamped within the limits.
+ */
+function clampScale(scale) {
+  return Math.min(5, Math.max(0.25, scale));
+}
+
+/**
+ * Computes vector between two points.
+ * @param {!Object} p1 The first point.
+ * @param {!Object} p2 The second point.
+ * @return {!Object} The vector.
+ */
+function vectorDelta(p1, p2) {
+  return {
+    x: p2.x - p1.x,
+    y: p2.y - p1.y
+  };
+}
+
+function frameToPluginCoordinate(coordinateInFrame) {
+  var container = $('plugin');
+  return {
+    x: coordinateInFrame.x - container.getBoundingClientRect().left,
+    y: coordinateInFrame.y - container.getBoundingClientRect().top
+  };
+}
+
+/**
  * Create a new viewport.
  * @constructor
  * @param {Window} window the window
@@ -49,6 +79,11 @@ function Viewport(window,
   this.fittingType_ = Viewport.FittingType.NONE;
   this.defaultZoom_ = defaultZoom;
   this.topToolbarHeight_ = topToolbarHeight;
+  this.prevScale_ = 1;
+  this.pinchPhase_ = Viewport.PinchPhase.PINCH_NONE;
+  this.pinchPanVector_ = null;
+  this.pinchCenter_ = null;
+  this.firstPinchCenterInFrame_ = null;
 
   window.addEventListener('scroll', this.updateViewport_.bind(this));
   window.addEventListener('resize', this.resize_.bind(this));
@@ -65,6 +100,19 @@ Viewport.FittingType = {
 };
 
 /**
+ * Enumeration of pinch states.
+ * This should match PinchPhase enum in pdf/out_of_process_instance.h
+ * @enum {number}
+ */
+Viewport.PinchPhase = {
+  PINCH_NONE: 0,
+  PINCH_START: 1,
+  PINCH_UPDATE_ZOOM_OUT: 2,
+  PINCH_UPDATE_ZOOM_IN: 3,
+  PINCH_END: 4
+};
+
+/**
  * The increment to scroll a page by in pixels when up/down/left/right arrow
  * keys are pressed. Usually we just let the browser handle scrolling on the
  * window when these keys are pressed but in certain cases we need to simulate
@@ -227,6 +275,29 @@ Viewport.prototype = {
   },
 
   /**
+   * @type {Viewport.PinchPhase} The phase of the current pinch gesture for
+   *    the viewport.
+   */
+  get pinchPhase() {
+    return this.pinchPhase_;
+  },
+
+  /**
+   * @type {Object} The panning caused by the current pinch gesture (as
+   *    the deltas of the x and y coordinates).
+   */
+  get pinchPanVector() {
+    return this.pinchPanVector_;
+  },
+
+  /**
+   * @type {Object} The coordinates of the center of the current pinch gesture.
+   */
+  get pinchCenter() {
+    return this.pinchCenter_;
+  },
+
+  /**
    * @private
    * Used to wrap a function that might perform zooming on the viewport. This is
    * required so that we can notify the plugin that zooming is in progress
@@ -266,6 +337,52 @@ Viewport.prototype = {
   },
 
   /**
+   * @private
+   * Sets the zoom of the viewport.
+   * Same as setZoomInternal_ but for pinch zoom we have some more operations.
+   * @param {number} scaleDelta The zoom delta.
+   * @param {!Object} center The pinch center in content coordinates.
+   */
+  setPinchZoomInternal_: function(scaleDelta, center) {
+    assert(this.allowedToChangeZoom_,
+        'Called Viewport.setPinchZoomInternal_ without calling ' +
+        'Viewport.mightZoom_.');
+    this.zoom_ = clampScale(this.zoom_ * scaleDelta);
+
+    var newCenterInContent = this.frameToContent(center);
+    var delta = {
+      x: (newCenterInContent.x - this.oldCenterInContent.x),
+      y: (newCenterInContent.y - this.oldCenterInContent.y)
+    };
+
+    // Record the scroll position (relative to the pinch center).
+    var currentScrollPos = {
+      x: this.position.x - delta.x * this.zoom_,
+      y: this.position.y - delta.y * this.zoom_
+    };
+
+    this.contentSizeChanged_();
+    // Scroll to the scaled scroll position.
+    this.position = {
+      x: currentScrollPos.x,
+      y: currentScrollPos.y
+    };
+  },
+
+  /**
+   *  @private
+   *  Converts a point from frame to content coordinates.
+   *  @param {!Object} framePoint The frame coordinates.
+   *  @return {!Object} The content coordinates.
+   */
+  frameToContent: function(framePoint) {
+    return {

[dpapad, 2016/11/09 01:12:27]

For a future CL cleanup, I think this entire class would benefit from a helper
Point class that can perform basic operations on its x,y (shift, scale, diff),
instead of duplicating operations on plain {x,y} objects. For example this could
look as

// Assuming this.position was also a Point instance.
return framePoint.shift(this.position).scale(this.zoom);

[Kevin McNee - google account, 2016/11/09 16:36:09]

I've added a TODO about this.

Acknowledged.

+      x: (framePoint.x + this.position.x) / this.zoom_,
+      y: (framePoint.y + this.position.y) / this.zoom_
+    };
+  },
+
+  /**
    * Sets the zoom to the given zoom level.
    * @param {number} newZoom the zoom level to zoom to.
    */
@@ -499,6 +616,79 @@ Viewport.prototype = {
   },
 
   /**
+   * Pinch zoom event handler.
+   * @param {!Object} e The pinch event.
+   */
+  pinchZoom: function(e) {
+    this.mightZoom_(function() {
+      this.pinchPhase_ = e.direction == 'out' ?
+                         Viewport.PinchPhase.PINCH_UPDATE_ZOOM_OUT :
+                         Viewport.PinchPhase.PINCH_UPDATE_ZOOM_IN;
+
+      var scaleDelta = e.startScaleRatio / this.prevScale_;
+      this.pinchPanVector_ =
+          vectorDelta(e.center, this.firstPinchCenterInFrame_);
+
+      var needsScrollbars = this.documentNeedsScrollbars_(
+          clampScale(this.zoom_ * scaleDelta));
+
+      this.pinchCenter_ = e.center;
+
+      // If there's no horizontal scrolling, keep the content centered so the
+      // user can't zoom in on the non-content area.
+      // TODO(mcnee) Investigate other ways of scaling when we don't have
+      // horizontal scrolling. We want to keep the document centered,
+      // but this causes a potentially awkward transition when we start
+      // using the gesture center.
+      if (!needsScrollbars.horizontal) {
+        this.pinchCenter_ = {
+          x: this.window_.innerWidth / 2,
+          y: this.window_.innerHeight / 2
+        };
+      } else if (this.keepContentCentered_) {
+        this.oldCenterInContent =
+            this.frameToContent(frameToPluginCoordinate(e.center));
+        this.keepContentCentered_ = false;
+      }
+
+      this.setPinchZoomInternal_(
+          scaleDelta, frameToPluginCoordinate(e.center));
+      this.updateViewport_();
+      this.prevScale_ = e.startScaleRatio;
+    }.bind(this));
+  },
+
+  pinchZoomStart: function(e) {
+    this.pinchPhase_ = Viewport.PinchPhase.PINCH_START;
+    this.prevScale_ = 1;
+    this.oldCenterInContent =
+        this.frameToContent(frameToPluginCoordinate(e.center));
+
+    var needsScrollbars = this.documentNeedsScrollbars_(this.zoom_);
+    this.keepContentCentered_ = !needsScrollbars.horizontal;
+    // We keep track of begining of the pinch.
+    // By doing so we will be able to compute the pan distance.
+    this.firstPinchCenterInFrame_ = e.center;
+  },
+
+  pinchZoomEnd: function(e) {
+    this.mightZoom_(function() {
+      this.pinchPhase_ = Viewport.PinchPhase.PINCH_END;
+      var scaleDelta = e.startScaleRatio / this.prevScale_;
+      this.pinchCenter_ = e.center;
+
+      this.setPinchZoomInternal_(
+          scaleDelta, frameToPluginCoordinate(e.center));
+      this.updateViewport_();
+    }.bind(this));
+
+    this.pinchPhase_ = Viewport.PinchPhase.PINCH_NONE;
+    this.pinchPanVector_ = null;
+    this.pinchCenter_ = null;
+    this.firstPinchCenterInFrame_ = null;
+  },
+
+  /**
    * Go to the given page index.
    * @param {number} page the index of the page to go to. zero-based.
    */