does Canvas support layering?

[KevinBoyd]

Does the Canvas class support layering or Depth?
For instance, if I draw a Box on the canvas and then overlap it with a Circle partially, is it possible to get the original box back, or is the overlapping Area overwritten by the Circle?

Are there any third party UI libraries that support layering?

[ingsaurabh]

No canvas doesnt support layering however you can acheive what U want by intelligent paintaing

Regarding 3rd party there are numerous LWUIT j2me Polish are name to few

[Tiger79]

well the GameCanvas does have something called a LayerManager which is to be used in combination with Layers (and Sprites)...
You might want to have a look at that ?

[KevinBoyd]

@ingsaurabh: what is intelligent painting?

@Tiger: More than sprites, I would like to have the ability to place custom components on the Canvas is it possible to do that.
For example can I create a CustomItem and place it on the canvas, or is there some way where I can place components on Canvas.

[rdrincon]

Quoting you:

For instance, if I draw a Box on the canvas and then overlap it with a Circle partially, is it possible to get the original box back, or is the overlapping Area overwritten by the Circle?

I would say that as Tiger mentions you need to use a LayerManager. This class allows you to put different items (Layers) pile them, and paint them according to your needs. Every Layer is independient and won't affect the other ones.

A Sprite it's just a kind of Layer, if you want to create your own, just inherit the Layer class and overwrite the paint() method.

Please check the GameCanvas documentation.

[KevinBoyd]

@rdrincon

The Sprite Class usually uses a image input either single or in the form of a film strip.

Is it possible for instance, If I was to make a custom button, then I inherit Layer without an image, and create a button by drawing a rectangular box and filling it with a pre-defined color and then I could use this on the canvas?

[rdrincon]

Yes, just inherit the Layer class and paint your box inside the paint method that you have to overwrite.

public class MyOwnLayer extends Layer{

public void paint(Graphics g){
//Paint your box with g
}

}

Now you will be able to add an instance of MyOwnLayer to any LayerManager.
And please, don't forget to make the MyOwnLayer instance visible

myOwnLayerInstance.setVisible(true);

[KevinBoyd]

@Ruben
Does that mean, this Layer instance is now a custom component and I can play with it and move, render and modify it at will on the canvas.

[ingsaurabh]

@ingsaurabh: what is intelligent painting?

its what every developer had to do while working on canvas because canvas most of the times developers k I talk bot myself at least I feel uncomfortable while working with canvas and all I have to create an illusion by customization

BTW if you use search functionality of forum most of post are related to canvas only

Nd of course Game Canvas support layering but U asked for canvas I replied for that only

[Tiger79]

well a layer in the GameCanvas is a Layer enveloping the whole screen area...
but fortunately within that screen-covering layer you can place your own items wherever you want...

[rdrincon]

Yes,
but then I'd rather recommend to use a sprite.
If you want to create your own component, then do the following.

1. Create an empty image

Image img = Image.createImage(100x100);

2. Get the Graphics of that Image

Graphics g= img.getGraphics();

3. Paint whatever you want in that graphics

4. Create a Sprite using the image img.

The good thing is that you can always modify the image getting the Graphics. Just add that Sprite to a LayerManager and you will be able to move it all over the screen, make it visible, overlap it with some other Sprite, whatever you want.

[grahamhughes]

Or... you can just draw the objects you want, in the paint() method. Draw them in order, from back to front. You can create a simple framework for this... something like:

public abstract class Component {
    private int x, y, w, h;

    protected abstract void paint(Graphics g);

    void parentPaint(Graphics g) {
        // record current state
        int cx = g.getClipX();
        int cy = g.getClipY();
        int cw = g.getClipWidth();
        int ch = g.getClipHeight();
        int tx = g.getTranslateX();
        int ty = g.getTranslateY();
        // set up for component paint
        g.translate(x, y);
        g.setClip(0, 0, w, h);

        paint(g);

        // put everything back how it was
        g.translate(tx - g.getTranslateX(), ty - g.getTranslateY());
        g.setClip(cx, cy, cw, ch);
    }
} 

public class Container extends Canvas {
    private Vector components = new Vector();
    private int backgroundColor;

    public void paint(Graphics g) {
        // paint background
        g.setColor(backgroundColor);
        g.fillRect(0, 0, getWidth(), getHeight());

        // paint components
        synchronized (components) {
            int size = components.size();
            for (int i = 0; i < size; i++) {
                Component c = (Component) components.elementAt(i);
                c.parentPaint(g);
            }
        }
    }
} 

[KevinBoyd]

@ Graham, Ruben, ingSaurabh, Tiger

Wow! Fantastic pieces of advise,
The codes that you have been dishing out has got me thinking, I will have to get used to the tips and tricks of J2ME programming.
Of course nothing can beat experience, but How do I pull up my socks, any good reference on J2ME programming, that teach your the caveats, the nuances...

Thanks!

[manjul_saini]

Hi, there is no foreground or background in J2ME what is available is your logic, just paint some thing first and other later, it will give you a layering effect, as stated by GH.

[KevinBoyd]

@Graham

// set up for component paint 
        g.translate(x, y); 
        g.setClip(0, 0, w, h); 

        paint(g); 

        // put everything back how it was 
        g.translate(tx - g.getTranslateX(), ty - g.getTranslateY()); 
        g.setClip(cx, cy, cw, ch); 

I did not understand the following code snippet, why do you translate back after painting?