as3 hitTestPoint detecting alpha - actionscript-3

Question

I am trying to make maze where the user draws with mouse and if they hit the wall it erases the line they just drew. I have a png file with alpha that creates the walls of the maze.
I need the user to draw on the alpha but when they hit a non alpha it will trigger an action and erase the line.
Here is the line I am having issues with:
if (myshape.hitTestPoint(theBall.x,theBall.y, true))
Here is the full code:
package
{
import flash.display.Sprite;
import flash.events.MouseEvent;
import flash.display.DisplayObject;
import flash.display.Graphics;
import flash.display.JointStyle;
import flash.display.LineScaleMode;
import flash.display.Shape;
import flash.display.Sprite;
import flash.events.*;
public class MazeClass extends Sprite
{
//Are we drawing or not?
private var drawing:Boolean;
public var myshape:Shape;
public var alreadyDrawn:Shape;
public var theBall:Ball = new Ball();
//alreadyDrawn = new Shape();
public function MazeClass()
{
if (stage)
{
myshape = new Shape();
myshape.graphics.lineStyle(12,0x000000);
addChild(myshape);
drawing = false;//to start with
stage.addEventListener(MouseEvent.MOUSE_DOWN, startDrawing);
stage.addEventListener(MouseEvent.MOUSE_MOVE, draw);
stage.addEventListener(MouseEvent.MOUSE_UP, stopDrawing);
//stage.addEventListener(Event.ENTER_FRAME, checkIt);
addChild(theBall);
}
}
public function startDrawing(event:MouseEvent):void
{
myshape.graphics.moveTo( mouseX, mouseY);
drawing = true;
}
public function draw(event:MouseEvent)
{
if (drawing)
{
//checkIt();
myshape.graphics.lineTo(mouseX,mouseY);
if (myshape.hitTestPoint(theBall.x,theBall.y, true))
{
trace("Hit A WALL!");
myshape.graphics.clear();
myshape.graphics.lineStyle(12, 0xFFFFFF);
myshape.graphics.moveTo(mouseX,mouseY);
}
}
}
public function stopDrawing(event:MouseEvent)
{
drawing = false;
}
}
}

Answer 1

Another option is to test the colour of the map bitmapdata pixel that corresponds to the "player's position" (the end of the drawn line, in this case):
var testPixel:uint = _myBitmapData.getPixel(xPosition, yPosition);
Or you can use .getPixel32 which includes alpha in the returned uint.

Answer 2

I FOUND A WORKING SOLUTION:
I found a working solution thanks to fsbmain. Thank you. I am posting my full code in hopes that this can help someone else.
In the end I had to use another movieClip rather than the mouse, but this worked for me. Now instead of drawing anywhere in the maze they have to drag a little character named Beau thru the maze. This works better for me.
It would be nice to know how to also detect if the mouse or the actual line I am drawing hit the wall as well. Maybe someone can make a suggestion. Nevertheless, thanks for helping me get this far.
The short and essential code to make my movieClip detect the alpha can be found here. It really is very short compared to other complicated options I found. Here is the link: http://www.mikechambers.com/blog/2009/06/24/using-bitmapdata-hittest-for-collision-detection/
package
{
import flash.display.Sprite;
import flash.events.MouseEvent;
import flash.display.DisplayObject;
import flash.display.Graphics;
import flash.display.JointStyle;
import flash.display.LineScaleMode;
import flash.display.Shape;
import flash.display.Sprite;
import flash.events.*;
import flash.events.KeyboardEvent;
import flash.ui.Keyboard;
import flash.events.TouchEvent;
import flash.ui.Multitouch;
import flash.ui.MultitouchInputMode;
import flash.desktop.NativeApplication;
import flash.system.Capabilities;
import flash.display.*;
import flash.geom.*;
import flash.display.BitmapData;
import flash.display.Bitmap;
import flash.geom.Matrix;
public class MazeClass extends Sprite
{
//Are we drawing or not?
private var drawing:Boolean;
public var myshape:Shape;
public var alreadyDrawn:Shape;
public var theMap:*;
public var swiper:Swiper = new Swiper();
public var Beau:littleBeau = new littleBeau();
//alreadyDrawn = new Shape();
public var currentGalleryItem:Number = 1;
public var totalGalleryItems:Number = 4;
public var redClipBmpData:BitmapData;
public var blueClipBmpData:BitmapData;
public var redRect:Rectangle;
public var blueRect:Rectangle;
public function MazeClass()
{
if (stage)
{
theMap = new MapOne();
myshape = new Shape();
myshape.graphics.lineStyle(33,0x0aa6df);
addChild(myshape);
drawing = false;//to start with
stage.addEventListener(MouseEvent.MOUSE_DOWN, startDrawing);
stage.addEventListener(MouseEvent.MOUSE_MOVE, draw);
stage.addEventListener(MouseEvent.MOUSE_UP, stopDrawing);
//stage.addEventListener(Event.ENTER_FRAME, checkIt);
stage.addEventListener(KeyboardEvent.KEY_UP, fl_OptionsMenuHandler);
Multitouch.inputMode = MultitouchInputMode.GESTURE;
addChild(theMap);
//theMap.height = stage.stageHeight - 200;
theMap.theStart.alpha = 0;
theMap.theFinish.alpha = 0;
addChild(swiper);
swiper.y = stage.stageHeight - swiper.height;
swiper.addEventListener(TransformGestureEvent.GESTURE_SWIPE, fl_SwipeToGoToNextPreviousFrame);
addChild(Beau);
Beau.x = theMap.theStart.x;
Beau.y = theMap.theStart.y - swiper.height;
Beau.addEventListener(MouseEvent.MOUSE_DOWN, BeauStartDrag);
Beau.addEventListener(MouseEvent.MOUSE_UP, BeauStopDrag);
redRect = theMap.getBounds(this);
redClipBmpData = new BitmapData(redRect.width,redRect.height,true,0);
redClipBmpData.draw(theMap);
blueRect = Beau.getBounds(this);
blueClipBmpData = new BitmapData(blueRect.width,blueRect.height,true,0);
blueClipBmpData.draw(Beau);
//blueClipBmpData.x = theMap.theStart.x;
//blueClipBmpData.y = theMap.theStart.y - swiper.height;
stage.addEventListener(Event.ENTER_FRAME, enterFrame);
}
}
public function enterFrame(e:Event):void
{
//Beau.x = mouseX;
//Beau.y = mouseY;
if (redClipBmpData.hitTest(new Point(theMap.x, theMap.y),
255,
blueClipBmpData,
new Point(Beau.x, Beau.y),
255
))
{
trace("hit");
clearAll();
//redClip.filters = [new GlowFilter()];
}
else
{
trace("No Hit");
}
}
public function BeauStartDrag(event:MouseEvent):void
{
Beau.startDrag();
drawing = true;
}
public function BeauStopDrag(event:MouseEvent):void
{
drawing = false;
Beau.stopDrag();
}
public function startDrawing(event:MouseEvent):void
{
myshape.graphics.moveTo( mouseX, mouseY);
}
//drawing = true;
public function draw(event:MouseEvent)
{
if (drawing)
{
//checkIt();
myshape.graphics.lineTo(mouseX,mouseY);
}
}
public function stopDrawing(event:MouseEvent)
{
//drawing = false;
}
public function fl_OptionsMenuHandler(event:KeyboardEvent):void
{
if ((event.keyCode == 95) || (event.keyCode == Keyboard.MENU))
{
NativeApplication.nativeApplication.exit(0);
}
}
public function clearAll()
{
myshape.graphics.clear();
myshape.graphics.lineStyle(12, 0x0aa6df);
myshape.graphics.moveTo(mouseX,mouseY);
Beau.x = theMap.theStart.x;
Beau.y = theMap.theStart.y - swiper.height;
drawing = false;
Beau.stopDrag();
}
public function fl_SwipeToGoToNextPreviousFrame(event:TransformGestureEvent):void
{
if (event.offsetX == 1)
{
if (currentGalleryItem > 1)
{
currentGalleryItem--;
trace("swipe Right");
clearAll();
removeChild(theMap);
theMap = new MapOne();
addChild(theMap);
theMap.height = stage.stageHeight - 200;
theMap.theStart.alpha = 0;
theMap.theFinish.alpha = 0;
addChild(Beau);
Beau.x = theMap.theStart.x;
Beau.y = theMap.theStart.y - swiper.height;
}
}
else if (event.offsetX == -1)
{
if (currentGalleryItem < totalGalleryItems)
{
currentGalleryItem++;
trace("swipe Left");
clearAll();
removeChild(theMap);
theMap = new MapTwo();
addChild(theMap);
theMap.height = stage.stageHeight - 200;
theMap.theStart.alpha = 0;
theMap.theFinish.alpha = 0;
addChild(Beau);
Beau.x = theMap.theStart.x;
Beau.y = theMap.theStart.y - swiper.height;
}
}
}
}
}