Swing Hacks

292

|

Chapter 8, Rendering

#56 Create a Magnifying Glass Component

HACK

Hacking the Hack

The only problem with the Robot approach is that it doesn’t limit itself to

capturing from the source component—it’ll take any onscreen pixels from

any application. That means that when you approach the edges of the

source component, you can pick up pixels from the desktop or other apps,

as seen in Figure 8-2.

Is this a problem? Some users will mind it, some won’t. To get rid of it,

you’ll need to smarten up

computeGrabRect( ) to bounds-check its right and

bottom edges (the top left is the cursor position, so it can never overshoot

the top or left of the component) by adding the untranslated point to the

proposed grab width and seeing if that is greater than the width of the

source component, and then doing the same for the height. This will take

some refactoring, since

computeGrabRect( ) doesn’t have access to the

untranslated point. Also, if you’re not necessarily going to be painting the

entire magnified component every time, you’ll have to erase it at the top of

paint( ), so you don’t have “crud” from the previous repaint left over after

this repaint.

Figure 8-2. Capturing pixels outside of the target component