J2ME Image / Graphics problem my misunderstanding?

Question

Hi,
Cannot find a J2me forum so I'm posting here :)
I have a mutable Image which I am using as an offscreen buffer. I initialise this image by setting the colour to white and calling the fillRect() method with the screen size as parameters. I do this in the constructor for my Canvas object.
In my paint() method I then draw only the extra things on the backbuffer (since I have already filled the image with white) and use the drawImage() method of the screens Graphics object to copy the backBuffer onto the screen of my device.
The problem is that text from the previous Form shows up, as if I have not filled the backBuffer with a white rectangle....
Code :
Initialisation :
backBuffer = Image.createImage(screenWidth,screenHeight);
Graphics g = backBuffer.getGraphics();
g.setColor( 255, 255, 255 );
g.fillRect( 0, 0, getWidth(), getHeight() );
In my paint() method :
Graphics saved = g; // Save the frame buffer
g = backBuffer.getGraphics();
g.setColor(255,0,0); // change the colour to red
// Draw the selection box.
g.drawRect(x,y,imageWidth,imageHeight);
saved.drawImage(backBuffer,0,0,Graphics.LEFT|Graphics.TOP);
Thanks,
Norris

Answer 1

backBuffer =
Image.createImage(screenWidth,screenHeight);
Graphics g = backBuffer.getGraphics();
g.setColor( 255, 255, 255 );
g.fillRect( 0, 0, getWidth(), getHeight() );you initialise the backBuffer size to screenWidth by screenHeight
yet, when you clear the image, you use the canvas's width and height
g.fillRect( 0, 0, getWidth(), getHeight() );this is wrong, you should either have
g.fillRect( 0, 0, backBuffer.getWidth(),backBuffer.getHeight());or
g.fillRect( 0, 0, screenWidth, screenHeight);rob,
p.s. next time, post MIDP questions in this forum...
http://forums.java.sun.com/forum.jsp?forum=50
Hi,
Cannot find a J2me forum so I'm posting here :)
I have a mutable Image which I am using as an
offscreen buffer. I initialise this image by setting
the colour to white and calling the fillRect() method
with the screen size as parameters. I do this in the
constructor for my Canvas object.
In my paint() method I then draw only the extra things
on the backbuffer (since I have already filled the
image with white) and use the drawImage() method of
the screens Graphics object to copy the backBuffer
onto the screen of my device.
The problem is that text from the previous Form shows
up, as if I have not filled the backBuffer with a
white rectangle....
Code :
Initialisation :
backBuffer =
Image.createImage(screenWidth,screenHeight);
Graphics g = backBuffer.getGraphics();
g.setColor( 255, 255, 255 );
g.fillRect( 0, 0, getWidth(), getHeight() );
In my paint() method :
Graphics saved = g; // Save the frame buffer
g = backBuffer.getGraphics();
g.setColor(255,0,0); // change the colour to red
// Draw the selection box.
g.drawRect(x,y,imageWidth,imageHeight);
saved.drawImage(backBuffer,0,0,Graphics.LEFT|Graphics.T
P);
Thanks,
Norris