CODEWITHSUNDEEP
actionscript-3bitmapdatahittest
Anonymous1
Anonymous1

Reputation: 3907

AS3 - Check if BitmapData is completely obscured by other BitmapData

I'm looking to check if a BitmapData object is completely obscured by a BitmapData object. Is there something like the hitTest function but that makes sure every pixel is covered instead of any pixel?

Edit: It is important that transparent pixels are not included when checking if the object is obscured.

Upvotes: 1

Views: 742

Answers (2)

user562566
user562566

Reputation:

It's actually a pretty simple solution after all! Basically what you do is just capture the pixel values of the overlapping bitmap in the rectangle area that the overlapped bitmap occupies. You then iterate over that vector of values and as long as you don't have a 0 (completely transparent pixel), then you've completely covered the bitmap underneath.

Here are the two bitmaps I used in this test:

Overlapping bitmap:
enter image description here

Overlapped bitmap:
enter image description here
Code:

import flash.display.BitmapData;
import flash.display.Bitmap;
import flash.events.MouseEvent;
import flash.geom.Point;
import flash.utils.ByteArray;
import flash.geom.Rectangle;

var coveredBitmapData:BitmapData = new CoveredBitmapData();
var coveringBitmapData:BitmapData = new CoveringBitmapData();


var coveringBitmap:Bitmap = new Bitmap(coveringBitmapData, "auto", true);
var coveredBitmap:Bitmap = new Bitmap(coveredBitmapData, "auto", true);

coveredBitmap.x = Math.random() * (stage.stageWidth - coveredBitmap.width);
coveredBitmap.y = Math.random() * (stage.stageHeight - coveredBitmap.height);

stage.addChild(coveredBitmap);
stage.addChild(coveringBitmap);

stage.addEventListener(MouseEvent.MOUSE_MOVE, onMouseMovement);

function onMouseMovement(e:MouseEvent):void
{
    coveringBitmap.x = mouseX - (coveringBitmap.width * .5);
    coveringBitmap.y = mouseY - (coveringBitmap.height * .5);

    checkIfCovering(coveringBitmap, coveredBitmap);
}

function checkIfCovering(bitmapA:Bitmap, bitmapB:Bitmap):Boolean
{
    //bitmapA is the covering bitmap, bitmapB is the bitmap being overlapped

    var overlappedBitmapOrigin:Point = new Point(bitmapB.x, bitmapB.y);

    var localOverlappedBitmapOrigin:Point = bitmapA.globalToLocal(overlappedBitmapOrigin);

    var overlappingPixels:Vector.<uint> = bitmapA.bitmapData.getVector(new Rectangle(localOverlappedBitmapOrigin.x, localOverlappedBitmapOrigin.y, bitmapB.width, bitmapB.height));

    if(overlappingPixels.length == 0) {
        //This means that there is no bitmap data in the rectangle we tried to capture. So we are not at all covering the underlying bitmap.
        return false;
    }

    var i:uint = 0;
    for(i; i < overlappingPixels.length; ++i) {
        if(overlappingPixels[i] == 0) {
            return false;
        }
    }

    return true;
}

Upvotes: 5

Marty
Marty

Reputation: 39458

So you want to see if object2 completely covers object1 (both Bitmaps)?

var left:Boolean = object2.x <= object1.x;
var top:Boolean = object2.y <= object1.y;
var right:Boolean = object2.x + object2.width >= object1.x + object1.width;
var bottom:Boolean = object2.y + object2.height >= object1.y + object1.height;


if(left && right && top && bottom)
{
    // Completely covered.
}

Upvotes: 3

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