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I have a problem with my android app which draws graphs of functions on a plane. To do this I use a custom View. The user can pan the coordinate system with touch. In the onDraw method, the coordinate system and the labels are drawn directly on the view's canvas, but the graphs themselves are buffered onto an additional bitmap(for performace reasons) - during the movement of the finger this bitmap is drawn onto the view's canvas translated so as to match the coordinate system, and the functions are redrawn only when the user releases the touch.

public void onDraw(Canvas canvas){
    if (start) {
        bitmap = Bitmap.createBitmap(getWidth(), getHeight(), Bitmap.Config.ARGB_4444);
        hCanvas = new Canvas(bitmap);
        start = false;
    }
    drawCoordinateSystem(canvas);
    drawFunctions(canvas,bitmap,hCanvas);
}

In onTouch event listener I call invalidate(). There is a boolean "moving", which is set to true for ACTION_UP and to false for ACTION_DOWN.

public void drawFunctions(Canvas canvas,Bitmap bitmap,Canvas hCanvas){
    if (moving) canvas.drawBitmap(bitmap,left+translateX,top+translateY,paint);
    else {
        hCanvas.drawColor(Color.TRANSPARENT,PorterDuff.Mode.CLEAR);

        //code for drawing the functions on hCanvas

        canvas.drawBitmap(bitmap,0,0,paint);
    }   
}

In ACTION_MOVE I calculate the translateX and translateY values appropriately.

Now where is the problem: If I compile the app for sdk 10, it works fine on all devices I tested it on(android 2.2-4.2 smartphones and tablets, virtual and physical). However, when I compile it for sdk 14, it works well for many devices, except for some tablets, where the coordinate system is drawn correctly, but somehow the bitmap containing the functions is not drawn on the view's canvas and the functions are not visible. The strange thing is, if I try to make a bitmap out of the view's canvas:

Bitmap bmp = this.getDrawingCache();
bmp.compress(Bitmap.CompressFormat.PNG, 100, out);

In the saved bitmap the functions are visible.

Another thing is - the issue occurs for i.a. Nexus 7, meanwhile on an AVD created with the preset Nexus 7 everything works fine.

What can be the problem?

Simon Sarris
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user2073589
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1 Answers1

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http://developer.android.com/reference/android/graphics/Bitmap.Config.html

I'll copy and paste the relevant part: Bitmap.Config ARGB_4444 This field was deprecated in API level . Because of the poor quality of this configuration, it is advised to use ARGB_8888 instead.
Bitmap.Config ARGB_8888 Each pixel is stored on 4 bytes.

Change your 4444 to 8888 and it should work.

Michael Dotson
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  • Thank you for your advice but it still doesn't work. What's more, the bitmap is quite big (bigger than the screen so the user gets an impression it's rendered in real time while scrolling) so it if I set ARGB8888 there are memory issues on certain devices. I used ARGB4444 to minimize the memory usage. Another thing - my problem seems to occur only on Tegra devices. Is there a way to buffer something before it is drawn to canvas othervthan using a bitmap? – user2073589 Feb 15 '13 at 17:24