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Bug 624451 Investigate changing displayport based on panning heuristics r=vingtetun r=mbrubeck

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This commit is contained in:
Benjamin Stover 2011-01-25 12:08:41 -08:00
parent 92154e70b7
commit f0c0edabf8
1 changed files with 75 additions and 10 deletions
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85
mobile/chrome/content/bindings/browser.xml
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@ -772,6 +772,69 @@
delete this.self._contentViews[this._id];
},
/**
* Given the cache size and the viewport size, this determines where the cache
* should start relative to the scroll position. This adjusts the position based
* on which direction the user is panning, so that we use our cache as
* effectively as possible.
*
* @param aDirection Negative means user is panning to the left or above
* Zero means user did not pan
* Positive means user is panning to the right or below
* @param aViewportSize The width or height of the viewport
* @param aCacheSize The width or height of the displayport
*/
_getRelativeCacheStart: function(aDirection, aViewportSize, aCacheSize) {
// Remember that this is relative to the viewport scroll position.
// Let's assume we are thinking about the y-axis.
// The extreme cases:
// |0| would mean that there is no content available above
// |aViewportSize - aCacheSize| would mean no content available below
//
// Taking the average of the extremes puts equal amounts of cache on the
// top and bottom of the viewport. If we think of this like a weighted
// average, .5 is the sweet spot where equals amounts of content are
// above and below the visible area.
//
// This weight is therefore how much of the cache is above (or to the
// left) the visible area.
let cachedAbove = .5;
// If panning down, leave only 25% of the non-visible cache above.
if (aDirection > 0)
cachedAbove = .25;
// If panning up, Leave 75% of the non-visible cache above.
if (aDirection < 0)
cachedAbove = .75;
return (aViewportSize - aCacheSize) * cachedAbove;
},
/** Determine size of the pixel cache. */
_getCacheSize: function(viewportSize) {
let self = this.self;
let contentView = this._contentView;
let cacheWidth = self._cacheRatioWidth * viewportSize.width;
let cacheHeight = self._cacheRatioHeight * viewportSize.height;
let contentWidth = contentView.contentWidth;
let contentHeight = contentView.contentHeight;
// There are common cases, such as long skinny pages, where our cache size is
// bigger than our content size. In those cases, we take that sliver of leftover
// space and apply it to the other dimension.
if (contentWidth < cacheWidth) {
cacheHeight += (cacheWidth - contentWidth) * contentHeight / contentWidth;
cacheWidth = contentWidth;
} else if (contentHeight < cacheHeight) {
cacheWidth += (cacheHeight - contentHeight) * contentWidth / contentHeight;
cacheHeight = contentHeight;
}
return { width: cacheWidth, height: cacheHeight };
},
/**
* The cache viewport is what parts of content is cached in the parent process for
* fast scrolling. This syncs that up with the current projection viewport.
@ -783,21 +846,23 @@
let contentView = this._contentView;
let viewportSize = this._getViewportSize();
let cacheWidth = self._cacheRatioWidth * viewportSize.width;
let cacheHeight = self._cacheRatioHeight * viewportSize.height;
let cacheSize = this._getCacheSize(viewportSize);
let cacheX = this._getRelativeCacheStart(this._pixelsPannedSinceRefresh.x, viewportSize.width, cacheSize.width) + contentView.scrollX;
let cacheY = this._getRelativeCacheStart(this._pixelsPannedSinceRefresh.y, viewportSize.height, cacheSize.height) + contentView.scrollY;
// Put the center point of the displayport at the center point
// of the viewport.
let cacheX = contentView.scrollX + viewportSize.width / 2 - cacheWidth / 2;
let cacheY = contentView.scrollY + viewportSize.height / 2 - cacheHeight / 2;
// Use our pixels efficiently and don't try to cache things outside of content
// boundaries.
let bounds = new Rect(0, 0, contentView.contentWidth, contentView.contentHeight);
let displayport = new Rect(cacheX, cacheY, cacheSize.width, cacheSize.height);
displayport.translateInside(bounds);
self.messageManager.sendAsyncMessage("Content:SetCacheViewport", {
scrollX: contentView.scrollX / self._scale,
scrollY: contentView.scrollY / self._scale,
x: cacheX / self._scale,
y: cacheY / self._scale,
w: cacheWidth / self._scale,
h: cacheHeight / self._scale,
x: displayport.x / self._scale,
y: displayport.y / self._scale,
w: displayport.width / self._scale,
h: displayport.height / self._scale,
scale: self._scale,
id: contentView.id
});