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Setting Background Image of View with onDraw Creates Finger Lag
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Matt M  
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 More options May 18 2011, 3:06 pm
From: Matt M <matthew.mag...@gmail.com>
Date: Wed, 18 May 2011 12:06:41 -0700 (PDT)
Local: Wed, May 18 2011 3:06 pm
Subject: Setting Background Image of View with onDraw Creates Finger Lag
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Hello,

I have a finger painting portion in my app that I built off of
FingerPaint.java
http://developer.android.com/resources/samples/ApiDemos/src/com/examp...

I am trying to set a background image using setBackgroundDrawable()
but upon doing so there is a significant amount of lag created when
painting (the tip of the paint lags behind the user's finger). I'm
calling view.setBackgroundDrawable in onCreate(). Any ideas on a fix?

Any help greatly appreciated!

Matt.


 
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Dianne Hackborn  
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 More options May 18 2011, 3:56 pm
From: Dianne Hackborn <hack...@android.com>
Date: Wed, 18 May 2011 12:56:17 -0700
Local: Wed, May 18 2011 3:56 pm
Subject: Re: [android-developers] Setting Background Image of View with onDraw Creates Finger Lag
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Um, run on a faster device.  Or don't do that.  It is a lot more work to
draw an image than fill a color...  and if your background image isn't the
exact size of the view, it also needs to be scaled which *significantly*
slows it down.

If you use the hardware accelerated drawing feature of HC then bitmaps are
basically not more expensive than drawing the screen, so now with HW acceler
turned on a standard part of the theme has a background bitmap.  However you
still really need to think about what you are doing -- Tegra 2 has enough
bandwidth I believe to paint the entire 1280x800 screen about 2.5 times, so
you really need to decide for each layer you add to your UI whether it is
actually worth it.

--
Dianne Hackborn
Android framework engineer
hack...@android.com

Note: please don't send private questions to me, as I don't have time to
provide private support, and so won't reply to such e-mails.  All such
questions should be posted on public forums, where I and others can see and
answer them.


 
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