Smooth scrolling on Android with slow onDraw

Question

I have a big custom View , and I draw a lot of rich text on it, many fonts, multiple colors and font sizes. I already optimized this drawing as much as possible. The redraw takes about 300ms.

This 300ms is OK for one time call, but since my View is bigger than the screen, it is inserted into the ScrollView, and now once the user scrolls with the finger, onDraw() is called repeatedly. Which gives very sloppy scrolling.

The same application was previously written for iOS, and iOS will not call onDraw (I think it is called drawRect() in iOS world), and all the drawn image is stored in some sort of buffer, so scrolling actually is very fast and ultra smooth, probably hardware accelerated.

So is there a way to achieve something like "No onDraw" smooth scrolling? I was thinking about drawing onto bitmap, and then blitting the bitmap during the scroll phases. But will it be any faster than drawing text? Are bitmaps HW accelerated on Android? What is the best approach to this kind of problem?

Thank you

Answer 1

Make the entire drawing into a Bitmap object using associated Canvas and in onDraw just flush this Bitmap . When you data changes, redraw everything into Bitmap .