[android-developers] Re: rotate portion of a bitmap

What you're trying to do is a common operation for graphics/games.  If you're doing a game, I would suggest just doing this in openGL -  you would create a texture altas out of 1 large bitmap (say 1024x1024), with your individual textures (or frames of a sprite) all packed in.  Then you can map from a part of that bitmap to a part of the surface you're drawing to, by specifying vertices.  You could then, instead of rotating the entire surface, just translate and rotate the destination vertices.

Some resources that help with this will be libgdx (open source graphics engine for Android) created by the author of Beginning Android Games, a book which was very helpful in explaining these things to me when I wanted to do something similar.

On Friday, April 6, 2012 9:07:53 PM UTC-4, elix wrote:

Hi

I was trying to find an appropriate way to draw a portion of a bitmap rotated onto the canvas. 

Rotating canvas does not seem appropriate for my situation; I am working on a game, there will be up to 30 soldiers on the screen. Rotating the whole canvas seperately for each of them does not seem nice.

I can't apply rotation to a matrix and use it in canvas.drawBitmap(source, matrix, paint) method. It works for the whole bitmap. I need to draw only a portion of bitmap at each frame. I am using sprite animation.

Somethings could be done using Bitmap.createBitmap(...) method but making bitmap creations continuously at each frame isn't nice. While writing these something came to my mind :), may be I could divide the frames into different bitmap objects at initialization phase using this createBitmap method, then apply rotation to these bitmaps using matrix.

Anyway, I will try this but I would be glad to hear better approaches.

--

Emre

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