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POAndroid: Rotation of image around the center
 

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  1. POAndroid: Rotation of image around the center
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    <p>I'm trying to rotate an image around the center. This works generally using RotateAnimation, but I want to have it a bit faster. I'm now using the SurfaceView pattern with a separate drawing thread.</p> <p>This is code, which draws the bitmap correctly (depending on the outer "heading")</p> <p>heading = angle in degrees, bitmap = the bitmap, w = width of the bitmap, h = height of the bitmap.</p> <pre><code> Matrix m = new Matrix(); m.preRotate(heading, w/2, h/2); m.setTranslate(50,50); canvas.drawBitmap(bitmap, m, null); </code></pre> <p>Drawback: The image is a circle and the code above produces visible aliasing effects...</p> <p>The code below is also rotating the image, but while rotating (say from 0 to 45 degrees clockwise) the center of the new image moves bottom/right. I suppose, the eccentric effect is due to the enlarged width/height of the new image ?? However, this code doesn't produce aliasing, if filter=true is set. Is there a way to use code #1 but have sort of anti-aliasing or use code #2 but getting rid of the center movement?</p> <pre><code> Matrix m = new Matrix(); m.preRotate(heading, w/2, h/2); m.setTranslate(50,50); Bitmap rbmp = Bitmap.createBitmap(bitmap, 0, 0, w, h, m, true); canvas.drawBitmap(rbmp, 50, 50, null); </code></pre> <p>UPDATE: As result of the discussion in this thread the correct version of code #2 (anti-aliasing <em>and</em> correct rotation) would look like this (offset of 50,50 omitted):</p> <pre><code> Matrix m = new Matrix(); m.setRotate(heading, w/2, h/2); Bitmap rbpm = Bitmap.createBitmap(bitmap, 0, 0, w, h, m, true); canvas.drawBitmap(rbpm, (w - rbpm.getWidth())/2, (h - rbpm.getHeight())/2, null); </code></pre> <p>Thanks.</p>
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    1. COWhat is the purpose of the setTranslate in the above code? I don't recall doing that for a simple rotation.
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    2. COHmm. Yes, this can be dropped... Thanks. Corrected.
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    3. COOh, sorry. Reverted my changes. setTranslate is necessary to offset the result to (50,50).
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