problem in repaint a part of canvas!!

[ahmedcse]

i am making a GUI canvas like forum with back ground image and sub-images
( to act as buttons) and i don't know when i add action to its sub-images
How to make the action is to repaint the canvas and change part of the screen only not all the screen like what i am facing here ( i just call repaint)
i.e it draws all the screen again and make repeat some sub-image in different location which i don't want to show when i want to show it in the same area but with another color or border style .

here my code:


public class DrawImage extends Canvas implements Runnable{
// Define your variables
Image source;
Font f;
int fontheight;
int mWidth= getWidth();
int mHeight= getHeight();
private static int i=0;
private String mMessage=" ";
public DrawImage(){
try{
source=getImage("images/ma3ak.PNG") ;
}catch(IOException e){
System.out.print("Couldnot Load the image");
e.printStackTrace();
}
f= Font.getFont(Font.FACE_MONOSPACE,i, Font.SIZE_MEDIUM);//Font.getDefaultFont();
fontheight=f.getHeight();
}
public Image getImage(String path) throws IOException {
return Image.createImage(path);
}

public void run() {

}
public void paint (Graphics g){
try {

g.drawImage(source, 0, 0, Graphics.TOP | Graphics.LEFT);
g.setColor(255,10, 10);
g.setFont(f);
g.drawString("Welcome To Ma3ak Mobile ", mWidth / 2, 0, Graphics.TOP | Graphics.HCENTER);
drawSubscriptions(g);
DrawGameItem(g);
drawTarfeeh(g);
//repaint();
} catch (IOException ex) {
ex.printStackTrace();
}
}
private void drawTarfeeh(Graphics g) throws IOException {
tarfeeh = resizeImage(Image.createImage("images/tarfeeh.PNG"), mWidth , mHeight/8) ;

g.drawImage(subscriptions, 0, mHeight / 2, Graphics.TOP | Graphics.LEFT);
}
private void drawSubscriptions(Graphics g) throws IOException {
subscriptions = resizeImage(Image.createImage("images/subscriptions.png"), mWidth, mHeight / Cool;

g.drawImage(subscriptions, 0, mHeight / 6, Graphics.TOP | Graphics.LEFT);
}
public Image getImage(String path) throws IOException {
return Image.createImage(path);
}

private Image resizeImage(Image src,int screenWidth,int screenHeight) {
int srcWidth = src.getWidth();
int srcHeight = src.getHeight();
Image tmp = Image.createImage(screenWidth, srcHeight);
Graphics g = tmp.getGraphics();
int ratio = (srcWidth << 16) / screenWidth;
int pos = ratio/2;

//Horizontal Resize

for (int x = 0; x < screenWidth; x++) {
g.setClip(x, 0, 1, srcHeight);
g.drawImage(src, x - (pos >> 16), 0, Graphics.LEFT | Graphics.TOP);
pos += ratio;
}

Image resizedImage = Image.createImage(screenWidth, screenHeight);
g = resizedImage.getGraphics();
ratio = (srcHeight << 16) / screenHeight;
pos = ratio/2;

//Vertical resize

for (int y = 0; y < screenHeight; y++) {
g.setClip(0, y, screenWidth, 1);
g.drawImage(tmp, 0, y - (pos >> 16), Graphics.LEFT | Graphics.TOP);
pos += ratio;
}
return resizedImage;

}//resize image

//then i repaint it with to user actions selecting a sub_image (as Button here)

[grahamhughes]

You should repaint the whole screen every time.

Graham.

[ahmedcse]

You should repaint the whole screen every time.

Graham.

i do already but it(repaint) draws canvas wrongly
(it adds sub-image in front of canvas).

[grahamhughes]

It just paints what your paint() code tells it to paint.

I recommend you don't resize the image every time you paint. Keep the paint quick, resize the images in advance.

You've wrapped all the code in try..catches, which might make you miss any exceptions that are being thrown at run time. You might have problems you're not aware of. I suggest you catch exceptions only if you're going to do something useful with them.

Graham.

[ahmedcse]

It just paints what your paint() code tells it to paint.

I recommend you don't resize the image every time you paint. Keep the paint quick, resize the images in advance.

You've wrapped all the code in try..catches, which might make you miss any exceptions that are being thrown at run time. You might have problems you're not aware of. I suggest you catch exceptions only if you're going to do something useful with them.

Graham.

Thanks graham
for your patient and advices
but what do u mean by resizing the images in advance ??
and how to repaint only a part of the screen ?

[grahamhughes]

Every time you paint(), you're loading the same two images, and resize them to the same sizes. You would be better to load the images and resize them somewhere else, and keep references to the resized images in non-local variables.

You don't repaint only part of the screen. You should always repaint everything.

Graham.

[ahmedcse]

You don't repaint only part of the screen.
You should always repaint everything.

Graham.

THEN IF I Repaint every thing i cannot change part of the screen
so how can i change part of the screen or repaint sub-Area of the screen!!

[grahamhughes]

Of course you can change part of the screen. You repaint some parts of the screen the same as the previous paint(), and some parts differently.

public class MyCanvas extends Canvas {
    // the object has "state"
    private boolean buttonPressed;

    // events change the state

    protected pointerPressed(int x, int y) {
        if (isInButtonArea(x, y)) {
            buttonPressed = true;
            repaint();
        }
    }

    protected pointerReleased(int x, int y) {
        buttonPressed = false;
        repaint();
    }

    // paint() draws a representation of the state

    protected void paint(Graphics g) {
        drawBackground(g);
        drawStaticElements(g);
        if (buttonPressed) {
            drawPressedButton(g);
        } else {
            drawReleasedButton(g);
        }
    }
}

When an event happens (in this case, the screen being touched or released), the state of the object changes, and a repaint() is issued.

The paint() method redraws the entire screen. Some parts are always drawn (those parts then never change), and other parts are drawn according to the state of the object.

I hope that helps.

Graham.

[ahmedcse]

thanks Graham
but i dont use a touch screen mobile i use normal canvas and default net-beans emulator
so i use the method below to make actions if u can help me to redraw every sub-image with user down or up buttons plz do thanks
this the method to specify user action:

protected void keyPressed(int keyCode) {
int gameAction = getGameAction(keyCode);
if (i < 0 || i > 2) {
i = 0;
}

switch (gameAction) {

case UP: {

i--;
mMessage = Integer.toString(i);
// repaint(mWidth/6, mHeight / 6, mWidth, mHeight ); is this right??
repaint();
}
break; // decrease i mMessage="UP";
case DOWN: {
i++; // increase i
mMessage = Integer.toString(i);
//repaint(mWidth/6, mHeight / 6, mWidth, mHeight );
repaint();
}
break;

case FIRE: {

if (i == 0) {
getDisplay().setCurrent(getSubscriptionForm());
repaint();
}
if (i == 1) {
getDisplay().setCurrent(getGamesForm());
repaint();
}
if (i == 2) {
getDisplay().setCurrent(getSuccessAlert("its counting " + mMessage));
repaint();
}
}
break; //to add action

default:
mMessage = "";
break;
}

}

then i want according to that to redraw sub-Image to show user that it is selected

[grahamhughes]

but i dont use a touch screen mobile i use normal canvas and default net-beans emulator

It doesn't matter, the principle is identical. keyPressed() is your event, and i (or mMessage?) is your state. The code in the event-handler changes the state, and the paint() method uses the state to decide what to draw on the Canvas.

So, as the value of "i" changes, you re-draw the entire screen, reading the value of "i" and drawing the screen accordingly.

Remember that the paint() method is called at many different times, not just when you call repaint(). It's called when the Canvas is setCurrent(). It is called when the Canvas is revealed after being completely or partially obscured by something else (such as a system alert, the volume control display, an SMS notification, an incoming call, etc.). For this reason, the paint() method needs to be able to paint the entire display at any time.

getDisplay().setCurrent(getSubscriptionForm());
repaint();

No need to repaint() when you're changing to a different Displayable. The Canvas isn't current anymore, so it can't repaint.

Graham.

[ahmedcse]

No need to repaint() when you're changing to a different Displayable. The Canvas isn't current anymore, so it can't repaint.

Graham.

hi Graham here i clear it
keyPressed() is my event and (i) is my state
how the paint() method uses the state to decide what to draw on the Canvas.
the value of "i" changes, i want to re-draw the entire screen, reading the value of "i" and drawing the screen accordingly.!!
how to do this?? is it by reversing the order of code
repaint() ;
then setCurrent(next Displayable) reversing does not work !!
or i repaint every (i) changes up or down what is the required parameters for repaint part of screen only while i have no Graphics(g) object in my keyPressed() method to use in editing my sub-images! how to override it ??

[grahamhughes]

First: forget the repaint() when you setCurrent(). repaint() tell the Canvas to repaint, but the Canvas won't be displayed anymore, because setCurrent() is replacing the Canvas with a different object (another Canvas, a Form, an Alert, or whatever).

Second: forget the whole idea of repainting part of the screen. paint() must be written to paint the entire screen every time. When "i" changes, you repaint the entire screen.

How do you want the screen to look for each value of "i"?

// state
private int i;

// handle event, update state, trigger repaint
protected void keyPressed(int keyCode) {
    switch (getGameAction(keyCode)) {
    case UP:
        i--;
        if (i < 0) {
            i = 2;
        }
        repaint();
        break;
    case DOWN:
        i++;
        if (i > 2) {
            i = 0;
        }
        repaint();
        break;
     case FIRE:
        // some code here...
        break;
    }
}

// paint the screen according to the state
protected void paint(Graphics g) {
    switch (i) {
    case 0:
        // paint screen for i = 0
        break;
    case 1:
        // paint screen for i = 1
        break;
    case 2:
        // paint screen for i = 2
        break;
    default:
        throw new IllegalStateException("paint: i = " + i);
    }
}

Graham.

[ahmedcse]

IT is working !!!!
Thanks graham
Thank you very Much