Glass Robot and getSCreenCapture

David Hill David.Hill at
Fri Mar 21 16:53:18 UTC 2014

I have been working on a problem with Robot.getScreenCapture() on a 565 ARM device, and while doing so, encountered a couple of questions which I will bring up:

Pixxls getScreenCapture(int x, int y, int width, int height, boolean isHiDPI)

I don't seem any real documentation that says how x,y + width,height should be treated when compared to the reality of the Screen.
What values of x,y + width,height  are reasonable ? I can picture any number of scenarios with them that would result in a box that does not fit within the Screen dimensions. The only implementing code I have seen checks to that the width & height are >= 1. Can I/Should I handle -x values ? What if the requested bounds exceed the screen ?

If we are making assumptions that the requested box is inside the screen.... then why don't we document that fact and add a check in the Robot class (instead of relying on the native impls).

If we are assuming the requested box does not have to lie within the screen bounds - what should the returned values be for the pixels outside the screen ? Pixel Black ? (Currently I think Lens would return 0x instead of 0xff000000)

My recommendation would be modify the JavaDoc contract to specify that the x,y and x+width, y+height must be within the screen bounds, with an IllegalArgumentException if out of bounds. This would be checked in Robot, prior to calling the native impls.

This code is "internal" API, so I expect the real impact would be on SQE.

David Hill <David.Hill at>
Java Embedded Development

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