Java Canvas Object: how to redraw?

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Ed Dana - 27 Feb 2005 06:30 GMT

I have created a small paint program in order to become more familiar
with Java. I am using the Canvas object to draw on, but whenever the
window is covered, I loose my work.

How do I preserve this information for repainting. I've tried getting
the Image from the Canvas and then tried to paint it back later, but
nothing is working.

Any and all clues appreciated.

Ed.

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Tjerk Wolterink - 27 Feb 2005 15:56 GMT

> I have created a small paint program in order to become more familiar
> with Java. I am using the Canvas object to draw on, but whenever the
[quoted text clipped - 7 lines]
>
> Ed.

You could create your own Image object,.. paint lines on that image, and then render that image
to the canvas.. A other solution.. but more complex .. is to create Objects that represent lines.. and a
Painting object.. And then call. Painting.drawMySoBeautifullPainting(Graphics g).. that is the vector approach

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Ed Dana - 27 Feb 2005 17:05 GMT

> You could create your own Image object,.. paint lines on that image, and
> then render that image
> to the canvas..

Thanks, I just tried that, and it helped but the application is slower now.

Since it is faster to directly paint on the canvas, what I'd really like
to do is get the image from the canvas after the brush stroke completes,
both for repainting and a redo function. Everything I've tried there has
failed.

Does anyone have any ideas on how I can extract an image from a canvas?
Everything I've tried so far has failed.

Ed.

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johndoe@example.com - 27 Feb 2005 18:09 GMT

>> You could create your own Image object,.. paint lines on that image, and
>> then render that image
[quoted text clipped - 9 lines]
> Does anyone have any ideas on how I can extract an image from a canvas?
> Everything I've tried so far has failed.

You can't.

The correct way to solve the problem (not only in Java, but in Win32,
MacOS X, X11, etc.) is to draw to a buffered image and blit that image
onto your canvas as required.

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Ed Dana - 27 Feb 2005 19:25 GMT

> The correct way to solve the problem (not only in Java, but in Win32,
> MacOS X, X11, etc.) is to draw to a buffered image and blit that image
> onto your canvas as required.

Thanks, that helps, but... How do I "blit" it to the canvas?

Ed.

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Ed Dana - 27 Feb 2005 19:52 GMT

>> The correct way to solve the problem (not only in Java, but in Win32,
>> MacOS X, X11, etc.) is to draw to a buffered image and blit that image
>> onto your canvas as required.
>
> Thanks, that helps, but... How do I "blit" it to the canvas?

By George, I think I've got it! :)

Rather than blitting, I'm drawing to the canvas first, and when the
stroke is completed, I draw to the Buffered Image. Seems to work so far.

Thanks all.

Ed.

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johndoe@example.com - 28 Feb 2005 19:51 GMT

> Thanks, that helps, but... How do I "blit" it to the canvas?

Graphics.drawImage()

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Java Canvas Object: how to redraw?

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