How to do scrolling in j2me canvas?

Question

I have created a sample application where I want to do scrolling, but I am not able to achieve the desired output.

I have tried the following code inside paint method >>>>>

g.translate(x,y);

and passing the value for variable 'y' in keydown and keyup event.

Can anyone help me out to do this?

most likely there's a bug in your code. If you show code you use in Canvas#keyPressed and in Canvas#paint, it will be easier to tell. Also, how do you test your app - do you use emulator? do you write log messages from code? — gnat, Feb 10 '12 at 07:51

Amir Uval · Answer 1 · 2012-02-22T20:57:14.283

Easiest way (though memory intensive) is to use MutableImage, and draw it with negative y coordinates.

Mutable image is just a new Image(w,h).
Then you get its Graphics context, using myImage.getGraphics(), and draw with this Graphics object. It serves as an off-screen buffer.

Than in paint(Graphics g), you call:

g.drawImage(0,y,...);

where you loop decreasing y on each system call to paint.
(don't block paint! - each call is one frame, and you're doing frame by frame animation
do the animation loop from another thread, where you decrease y, than call repaint(), and sleep).

score 1 · Accepted Answer · edited Apr 25 '12 at 06:35

1

Have you tried with decrementing the value of Y in keyUP and calling repaint() method also do same with keyDown but now the value of Y will be decrementing and call repaint() method.

Use the g.translate(x, changingYvalue);

try this.

edited Apr 25 '12 at 06:35

Lucifer

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answered Feb 24 '12 at 12:57

iLearner

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score 0 · Answer 3 · answered Feb 24 '12 at 13:22

I think that the scrollbar should be drawn inside the paint method. And you implement the keyReleased method when clicking the arrow of the scrollbar. To implement the scrolling I would prefer call repaint(); and I will manage the paint method with boolean or some other type of private variable.

How to do scrolling in j2me canvas?

3 Answers3