Java sampling pixel color in swing

Question

I have to create a special TextFieldUI that draws an image as the background. That image contains some alpha components. However, whenever a character is written in that text field, first it redraws the background and then draws the character. This is fine when the background contains no alpha components, but after a few characters have been typed, the alpha areas sum up to become black.

The only way I can see around this is in the paintBackground method of TextfieldUI (which I'm overriding), I have to first sample the color of the background at that location, paint the entire graphics component that color, and then paint my background.

1. Does anyone know how to sample the color of a pixel when all I have access to is the Graphics object?

2. Is there a better way to draw a custom image as the textfield background other than overriding paintBackground in TextfieldUI?

Thanks

Answer 1

我以前没有尝试过，但是Swing是建立在AWT之上的，而Robot类有一种在AWT中采样特定像素的方法

Answer 2

Well, I don't know what your custom code looks like in the paintBackground method, but I would make sure you fill in the text field background before you draw the image.

I'll let you decide if its "better" or not, but you can use the Background Panel which allows you to add an image to a panel. Then you add the text field to the panel (the text field is automatically made non-opaque so the image shows through). Then you add the panel to the GUI.

If that doesn't work then it would be nice to have a demo of your code so we can see whats actually happening.

Answer 3

When you override paintBackground, you're calling the superclass version first, right? It already lays down a background-color rectangle that would give your image a fresh-start.

Rather than 'sampling' the background color, it's probably already correct (the superclass paintBackground code gets it from the parent component if not locally set). If that default is not correct, set it in initial interface construction. (Your field isn't being overlaid on other complicated arbitrary interface of unknown solid colors, is it?)