Hi guys,

I'm new to this board, tried searching for possible threads that could be of help, but even implementing the ideas from the first thread in search results didn't help. I know it's more of a coding issue, the program runs, but collisions are not detected. And well, that's quite necessary :) Can anyone help?

I've posted only an excerpt of the code. Should more be necessary, I'll definitely post more!

FYI, the draw-function resides in a class, and is called from the applet's main draw-function.

Code:

    void draw() {
        order();
        NewPie pie;
        for (int i = 0; i < this._pies.length; i++) {
            pie = (NewPie) this._pies[i];
            pie.setDiameter(this._maxDiam - i * (this._maxDiam / this._pies.length));
            if (!pie.isDrawn()) {
                checkCollision(pie);
            }
            pie.draw(this._items);
        }
        this.evaluateMouseMove();
    }
    
    void checkCollision(NewPie pie) {
        NewPie temp;
        float tempX = random(pie.getDiameter()/2, width - pie.getDiameter()/2);
        float tempY = random(pie.getDiameter()/2, height - pie.getDiameter()/2);
        boolean isColliding = false;
        for (int i = 0; i < this._pies.length; i++) {
            temp = (NewPie) this._pies[i];
            if (temp.isDrawn() &&  !temp.equals(pie)) {
                if (dist(temp.getPosX(), temp.getPosY(), tempX, tempY) < (temp.getDiameter() / 2 + pie.getDiameter() / 2)) {
                    checkCollision(pie);
                    isColliding = true;
                }
            }
        }
        if (isColliding) {
            pie.setPosition(tempX, tempY);
        }
    } 

Any help greatly appreciated, I've been breaking my head over this for hours!

Two remarks:
- this.stuff is not necessary in Java, just use stuff.
Well, some people like to use this form to be explicit/symmetrical, but I see it more as "visual noise" distracting code reading. To each their own.
- in checkCollision(), you call checkCollision(), which is a recursive call. Not sure if it is intended... Probably not, as you already computed the dist and set the isColliding boolean.

@PhiLho, I know, but I got trained as a software engineer and the use of this is like a religion
The recursive call to checkCollision is indeed necessary, since there are multiple elements being drawn, and collision can occur with others + on different positions (each time they are given a new random position). However, you are correct that the loop should stop as soon as a collision is detected. I did that now.

@stopfocus and @Bejoscha, your sketches and code helped me through all of this. Elastic collisions aren't necessary, but the way your code browses through all the objects, is much more efficient than mine. Thanks for that!

In general, the collision detection works like a charm now. The only issue occurs when dragging the elements around, and recursively checking for collisions again. Got some nasty StackOverflowException... I'll try to fix it first myself, though!