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POUnderstanding Android's Canvas.saveLayer(...)
 

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  1. POUnderstanding Android's Canvas.saveLayer(...)
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    <p>I am hoping the saveLayer methods will allow me to do draw onto different "layers" and then once the drawing has finished, merge the layers with the canvas in whichever order i choose.</p> <p>The obvious question is "why dont you just rearrange your drawing operations instead?" The answer is I can't:</p> <p>I have a Path that I need to draw onto a Canvas. In the background/lowest z-index I want to draw the path closed and with a few additional points using a fill style. Then on top of that, I want to draw an outline of only the points that were originally in the Path.</p> <p>Since I cannot undo the adding of points to the Path, my only choices are to clone the path, or to draw to a second layer which can later be placed on top of everything else.</p> <p>saveLayer() seems to offer that functionality but it doesnt behave the way I was expecting. The basic flow of my operations is like this:</p> <pre><code>int overlay = canvas.saveLayer(...); // drawing operations for my uppermost layer ... int background = canvas.saveLayer(...); // drawing operations for my background layer ... // merge the offscreen background bitmap with the canvas: canvas.restoreToCount(background); // merge the offscreen overlay bitmap with the canvas: canvas.restoreToCount(overlay); </code></pre> <p>When the code runs, the ordering of background and overlay have not changed at all; what gets drawn first is at the bottom and what gets drawn last is on top. Even stranger to me is that I can completely comment out both calls to restoreToCount() and nothing changes. According to the javadoc, nothing should be drawn to the canvas until a balancing restore() is invoked.</p> <p>Obviously I am completely misunderstanding the function of this method. Can anybody help me to understand saveLayer's usage, or perhaps suggest an alternate way to layer my drawing operations?</p> <p>Thx! Nick</p>
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