Tiling a Bitmap on a Canvas

android canvas bitmap tiling
Paul Mennega picture Paul Mennega · Jan 29, 2011 · Viewed 10k times · Source

I would like to create a 'graph paper' look to the Bitmap I am drawing via a Canvas, and trying to figure out the best way to do this.

I can't pass a source Bitmap containing the graph paper background to the Canvas constructor, as I am getting the Canvas in a SurfaceView via the .lockCanvas() call.

Some solutions I've tried:

  • I've tried implementing this solution in my SurfaceView's Thread.run(), but the issue I believe is when the BitmapDrawable is converted to a Bitmap... it loses the tiling properties.

    canvas = mSurfaceHolder.lockCanvas(null); BitmapDrawable TileMe = new BitmapDrawable(BitmapFactory.decodeResource(getResources(), R.drawable.editor_graph)); TileMe.setTileModeX(Shader.TileMode.REPEAT); TileMe.setTileModeY(Shader.TileMode.REPEAT);

    Bitmap b = TileMe.getBitmap(); canvas.drawBitmap(b, 0, 0, null);

  • If I use the Canvas.drawBitmap method that takes a destination RectF as a parameter, it looks like the bitmap will be tiled to fill the RectF... but how do I declare a RectF reliably that fills the entire view area?

  • Setting the Activities background to the desired graph paper look also doesn't work, as the bitmap/canvas layout is opaque and blocks that from being seen.

Any ideas how to achieve this?

Answer

Romain Guy picture Romain Guy · Jan 29, 2011

You have two easy solutions:

  • Either use a BitmapDrawable, but instead of extracting the Bitmap, just call BitmapDrawable.draw(Canvas). Don't forget to set the drawable's bounds to fill your drawing area.
  • Create a Paint with a BitmapShader and draw a rectangle with it (this is basically what BitmapDrawable does).

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