create an image out of a portion of a JPanel

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fahruz@hotmail.com - 12 Jan 2005 09:32 GMT

Hi,

This has been addressed to some extent in the past, save for the
following point:

how does one create an image from a specified area of a JPanel without
retrieving the whole graphics data?

The easy, straightforward way would be:

BufferedImage image = new BufferedImage(jpanel.getWidth(),
jpanel.getHeight(), BufferedImage.TYPE_INT_RGB);
Graphics2D g2 = image.createGraphics();
paint(g2);
image = image.getSubimage(x, y, width, height);

which is highly inefficient if the panel is very large and all the
graphic data has to be copied to the BufferedImage before cropping.
Isn't there a direct way to paint only a specific area inside a
Graphics object?

Thx.

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Andrey Kuznetsov - 12 Jan 2005 10:06 GMT

> This has been addressed to some extent in the past, save for the
> following point:
[quoted text clipped - 13 lines]
> Isn't there a direct way to paint only a specific area inside a
> Graphics object?

you can make following:

BufferedImage image = new BufferedImage(width, height,
BufferedImage.TYPE_INT_RGB);
Graphics2D g2 = image.createGraphics();
g2.translate(x, y);
paint(g2);
g2.dispose();

if you need to make this often, then don't create image every time.

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Andrey Kuznetsov
http://uio.dev.java.net Unified I/O for Java
http://reader.imagero.com Java image reader
http://jgui.imagero.com Java GUI components and utilities

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fahruz@hotmail.com - 13 Jan 2005 03:06 GMT

Thanks for the answer Andrey but this doesn't work. It seems you're
trying to translate the coordinates of the target image's graphics
object whereas it should probably be the jpanel's. Maybe
Graphics2D g2p = (Graphics2D)jpanel.getGraphics();
g2p.translate(x,y);

But then, how to copy the rectangle portion of the jpanel's graphics
into the image's graphics?

I might also point out there was a small mistake in my code example. I
meant to call the jpanel's paint method

BufferedImage image = new BufferedImage(jpanel.getWidth(),
jpanel.getHeight(), BufferedImage.TYPE_INT_RGB);
Graphics2D g2 = image.createGraphics();
jpanel.paint(g2); // instead of just paint(g2);
image = image.getSubimage(x, y, width, height);

Thx.

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Andrew Thompson - 13 Jan 2005 08:26 GMT

> I might also point out there was a small mistake in my code example.

You might instead post an SSCCE, it will save time.
<http://www.physci.org/codes/sscce.jsp>

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Andrew Thompson
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fahruz@hotmail.com - 14 Jan 2005 08:11 GMT

You might instead RTTBR (Read The Thread Before Replying), it will save
time. My code is not the problem here. We're looking for efficient ways
to address the issue described in the first question.

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Andrew Thompson - 14 Jan 2005 10:12 GMT

> You might instead RTTBR (Read The Thread Before Replying), ..

Many things might happen.

You for example, might quote a little of what you are replying to,
as I have above - to provide context to the reader. Threads from
earlier conversations drop off a lot of servers.

You might even (by use of effective communication) resolve the
technical issue.

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Andrey Kuznetsov - 14 Jan 2005 09:47 GMT

> Thanks for the answer Andrey but this doesn't work.

which result you got?

> It seems you're
> trying to translate the coordinates of the target image's graphics
> object whereas it should probably be the jpanel's. Maybe
> Graphics2D g2p = (Graphics2D)jpanel.getGraphics();
> g2p.translate(x,y);

surely this is the wrong way

> But then, how to copy the rectangle portion of the jpanel's graphics
> into the image's graphics?

you can't

> I might also point out there was a small mistake in my code example. I
> meant to call the jpanel's paint method
[quoted text clipped - 4 lines]
> jpanel.paint(g2); // instead of just paint(g2);
> image = image.getSubimage(x, y, width, height);

this is not the problem.

Signature

Andrey Kuznetsov
http://uio.dev.java.net Unified I/O for Java
http://reader.imagero.com Java image reader
http://jgui.imagero.com Java GUI components and utilities

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Andrey Kuznetsov - 14 Jan 2005 10:47 GMT

> BufferedImage image = new BufferedImage(width, height,
> BufferedImage.TYPE_INT_RGB);
> Graphics2D g2 = image.createGraphics();
> g2.translate(x, y);
> paint(g2);
> g2.dispose();

if it didn't worked, may be you should change this a little:
g2.translate(-x, -y);

Signature

Andrey Kuznetsov
http://uio.dev.java.net Unified I/O for Java
http://reader.imagero.com Java image reader
http://jgui.imagero.com Java GUI components and utilities

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create an image out of a portion of a JPanel

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