Clearing the last graphic drawn? (Undo/Redo drawing)

Question

public function drag(e:MouseEvent)
    {
        lineDraw(mouseX, mouseY);
        e.updateAfterEvent();

    }
    public function lineDraw(X:int, Y:int):void
    {
        currentX = X;
        currentY = Y;

        graphics.lineStyle(size, color)
        graphics.moveTo(previousX, previousY)
        graphics.lineTo(currentX, currentY)

        previousX = currentX;
        previousY = currentY;
    }

Very simple code I made that allows me to draw lines with my mouse. Function drag is triggered on MOUSE_MOVE after MOUSE_DOWN.

My question is: how would I go about clearing the last line drawn? Basically, a ctrl+z/undo function that can be repeat as many times as i want.

Would I have to rewrite my code completely and push every single line drawn into an array, and then work my way backwards through the array, removing lines as I click "undo"? Or is there another better, easier solution to this?

Thanks! :)

Answer 1

Here is an example: See code comments for explanations

private var undoStates:Vector.<Shape> = new Vector.<Shape>(); //holds all your undo states (HAS TO BE SHAPE SINCE AS3 DOESN"T LET YOU ISNTANTIATE A GRAPHICS OBJECT DIRECTLY)
private var redoStates:Vector.<Shape> = new Vector.<Shape>(); //holds all your redo states
private var undoLevels:int = 1; //how many undo levels you'd like to have
private var redoLevels:int = 1;

public function undo() {
    if (undoStates.length > 0) {  //make sure there is an undo state before preceeding
        //add redo state
        redoStates.push(getState());

        //if redo states are more than redoLevels, remove the oldest one
        if (redoStates.length > redoLevels) redoStates.splice(0, 1);

        //make the the last undo state the current graphics
        graphics.clear(); //not sure if this line is required, can't recall if copyFrom clears first
        graphics.copyFrom(undoStates.pop().graphics); //pop removes the last item from the array and returns it
    }
}

public function redo() {
    if (redoStates.length > 0) {
        //add undo state
        addUndo();

        //make the the last undo state the current graphics
        graphics.clear(); //not sure if copy from (the next line) clears or not
        graphics.copyFrom(redoStates.pop().graphics);
    }
}

private function getState():Shape{
    var state:Shape = new Shape();
    state.graphics.copyFrom(graphics);  //copy the current graphics into a new Graphics object
    return state;
}

private function addUndo():void {
    undoStates.push(getState()); //add the current state to the undo array

    //if more undo states than undoLevels, remove the oldest one
    if (undoStates.length > undoLevels) undoStates.splice(0, 1);
}

public function lineDraw(X:int, Y:int):void {
    currentX = X;
    currentY = Y;


    //create undo state before we draw more
    addUndo();

    graphics.lineStyle(size, color)
    graphics.moveTo(previousX, previousY)
    graphics.lineTo(currentX, currentY)


    previousX = currentX;
    previousY = currentY;
}