Can I draw outside the bounds of an Android Canvas

Question

I'm porting an app written in a graphics environment that allows drawing to happen outside the bounds of the clipping rectangle. Any way to do this in Android?

Atmospherics

Answer 1

try to set

android:clipChildren="false" 

to the parent view

Prophylactic

Answer 2

To draw outside the bounds, you need to expand the clipRect of the canvas.

Check out the overloaded clipRect methods on the Canvas class.

Note - You will need to specify the Region operation because the default operation is INTERSECT. So something like this:

Rect newRect = canvas.getClipBounds();
newRect.inset(-5, -5)  //make the rect larger

canvas.clipRect (newRect, Region.Op.REPLACE);
//happily draw outside the bound now

Puzzle

It doesn't work at all. I just resize canvas with (-2000, -2000) parameters, then translate it but the image I draw is still clipped. – Alanna

but if you do that on every onDraw(Canvas canvas) then aren't you making the computer do a lot of extra work ? – Inerrant

@SomeoneSomewhere i am not sure what the effect on performance is when you change clip rects (esp. with HA on vs software rendering). but this should be simple to measure through profiling. – Puzzle

This works the first time Invalidate is called. Subsequent calls do not work. – Yacano

Region.Op.REPLACE got deprecated at API >= 26 Do you have another solution? Im running out all SOF and didnt found yet – Osmo

Answer 3

You can draw where you like, but nothing will be saved outside the clipping rectangle.

Preparator

Answer 4

The answer @numan gave is almost ok, the problem is memory allocation with that approach, so we should be doing this, instead:

// in constructor/elsewhere
Rect newRect = new Rect();

// in onDraw
canvas.getClipBounds(newRect);
newRect.inset(0, -20);  //make the rect larger
canvas.clipRect(newRect, Region.Op.REPLACE);

That solves the problem :-)

Gallantry

How to init newRect ? – Kennakennan

Ok, I guess the point here that newRect is allocated once per object init, instead of allocating it each time onDraw is called. – Kennakennan

Region.Op.REPLACE is deprecated. It doesn't work anymore! – Rexer

Answer 5

If you want to draw text out of bounds in TextView, you should be doing this instead:

<TextView
    ...
    android:shadowColor="#01000000"
    android:shadowDx="100" // out of right bound
    android:shadowDy="0"
    android:shadowRadius="1"
.../>

It's not working to use clipRect() like @numan's answer because TextView clip it's own rect in onDraw():

if (mShadowRadius != 0) {
    clipLeft += Math.min(0, mShadowDx - mShadowRadius);
    clipRight += Math.max(0, mShadowDx + mShadowRadius);

    clipTop += Math.min(0, mShadowDy - mShadowRadius);
    clipBottom += Math.max(0, mShadowDy + mShadowRadius);
}

canvas.clipRect(clipLeft, clipTop, clipRight, clipBottom);

Last but not least, Don't forget to set android:clipChildren="false" and android:clipToPadding="false" in your parent ViewGroup

Avidin

[SOLVED] WOKED! ((ViewGroup) parent).setClipChildren(true); ((ViewGroup) parent).setClipToPadding(true); solved for my using this when I needed to draw over the other views at same hierarchy thx ! – Osmo

Answer 6

If what you want is just draw outside the view bounds (programmatically), cut the long story short.

parentLayout.setClipChildren(false);

or via xml :

 android:clipChildren="false"

Tracietracing