Creating a parallax on a tiling background - apache-flex

Question

I am using the blitting technique that Jeff from 8bitrocket.com uses for creating tiles. I am trying to paint 2 layers of bitmapdata onto a bitmap. One the first layer is the background ( 1 image). and the second layer is the tiles. In that class below. the updateMap is the method that gets called in the loop to repaint the image.
package com.eapi
{
/**
* ...
* #author Anthony Gordon
*/
import com.objects.XmlManager;
import flash.display.MovieClip;
import flash.display.Sprite;
import flash.events.*;
import flash.display.BitmapData;
import flash.display.Bitmap
import flash.geom.Rectangle;
import flash.geom.Point;
import flash.display.DisplayObject;
public class EngineApi extends MovieClip
{
public var images:Array;
public var world:Array;
//w stands for world, how big it is in columns and rows
private var wCols:Number = 50;
private var wRows:Number = 16;
public var wWidth:Number;
public var wHeight:Number;
//v stands for view, which means your field of view
public var vRows:Number;
public var vCols:Number;
public var vWidth:Number = 540;
public var vHeight:Number = 360;
//how big your indivual tile is
public var tileW:Number = 80;
public var tileH:Number = 80;
public var offsX:Number = 0;
public var offsY:Number = 0;
public var xEnd:Number = 0;
public var yEnd:Number = 0;
public var tilex:int;
public var tiley:int;
public var scrollx:Number = 0;
public var scrolly:Number = 0;
private var screen:Bitmap;
private var canvas:BitmapData;
private var buffer:BitmapData;
public var mapHolder:Array;
private var scrollLoop:Boolean;
private var minLoop:Number;
private var maxLoop:Number;
public var currentMap:Number = 0;
private var queue:Array;
public var currentCol:Number = 0;
public var currentRow:Number = 0;
public var enviroment:Array;
public var currentTileSheet:Number = 0;
private var layer1:Sprite;
private var layer2:Sprite;
private var layer3:Sprite;
private var layer4:Sprite;
private var layer5:Sprite;
public var background:BitmapData
protected var stageObject:Array;
protected var gameObjects:Array;
public function EngineApi(w:Number = 540,h:Number = 360, tw:Number = 50, th:Number = 50)
{
stageObject = new Array();
gameObjects = new Array();
//Add Layers
layer1 = new Sprite();
layer2 = new Sprite();
layer3 = new Sprite();
layer4 = new Sprite();
layer5 = new Sprite();
//end
images = new Array();
vWidth = w;
vHeight = h;
tileW = tw;
tileH = th;
queue = new Array();
mapHolder = new Array();
vCols = Math.floor(vWidth/tileW);
vRows = Math.floor(vHeight/tileH);
wWidth = wCols * tileW;
wHeight = wRows * tileH;
canvas = new BitmapData(vWidth,vHeight,true,0x000000);
buffer = new BitmapData(vWidth + 2 * tileW, vHeight + 2 * tileH ,false,0x000000);
screen = new Bitmap(canvas);
addChild(screen);
addChild(layer1);
addChild(layer2);
addChild(layer3);
addChild(layer4);
addChild(layer5);
}
public function addGameChild(object:IGameObject, layer:Number):void
{
switch(layer)
{
case 1:
layer1.addChild(DisplayObject(object));
break;
case 2:
layer2.addChild(DisplayObject(object));
break;
case 3:
layer3.addChild(DisplayObject(object));
break;
case 4:
layer4.addChild(DisplayObject(object));
break;
case 5:
layer5.addChild(DisplayObject(object));
break;
default:
}
if (object.IsDisplay == true)
gameObjects.push(object);
stageObject.push(object);
}
public function UpDateMap():void
{
offsX += scrollx;
offsY += scrolly;
tilex = int(offsX/tileW);
tiley = int(offsY/tileH);
xEnd = tilex + vWidth;
yEnd = tiley + vHeight;
var tileNum:int;
var tilePoint:Point = new Point(0,0);
var tileRect:Rectangle = new Rectangle(0, 0, tileW, tileH);
var rowCtr:int=0;
var colCtr:int=0;
for (rowCtr=0; rowCtr <= vRows; rowCtr++) {
for (colCtr = 0; colCtr <= vCols; colCtr++) {
currentCol = colCtr+tilex;
currentRow = rowCtr+tiley;
tileNum = mapHolder[currentMap][rowCtr+tiley][colCtr+tilex];
tilePoint.x = colCtr * tileW;
tilePoint.y = rowCtr * tileH;
tileRect.x = int((tileNum % 100))* tileW;
tileRect.y = int((tileNum / 100))* tileH;
buffer.copyPixels(images[currentTileSheet],tileRect,tilePoint);
}
}//End Loop
var bgRect:Rectangle = new Rectangle(0, 0, 544, 510);
var bgPoint:Point = new Point(0, 0);
var bufferRect:Rectangle = new Rectangle(0,0,vWidth,vHeight);
var bufferPoint:Point = new Point();
bufferRect.x = offsX % tileW;
bufferRect.y = offsY % tileH;
canvas.copyPixels(background,bgRect,bgPoint);
canvas.copyPixels(buffer,bufferRect,bufferPoint);
}//End UpdateMap
public function StartRender():void
{
addEventListener(Event.ENTER_FRAME, loop);
}
protected function loop(e:Event):void
{
UpDateMap();
UpdateObjects();
}
protected function UpdateObjects():void
{
for (var i:Number = 0; i < stageObject.length; i++)
{
stageObject[i].UpdateObject();
}
for (var g:Number = 0; g < stageObject.length; g++)
{
if (stageObject[g].Garbage && stageObject[g].IsDisplay)
{
removeChild(DisplayObject(stageObject[g]));
stageObject[g] = null;
}
else if (stageObject[g].Garbage == true && stageObject[g].IsDisplay == false)
{
stageObject[g] = null;
}
}
}
public function StopRender():void
{
removeEventListener(Event.ENTER_FRAME, loop);
}
}
}
It's not the complete code, but if I remove canvas.copyPixels(background,bgRect,bgPoint); or canvas.copyPixels(buffer,bufferRect,bufferPoint); I can see either or. If I paint them both then I can only see the one that painted last. My tile image is 128 x 32. 0 - 3. array 3 is transparent image. I used that hoping that I could see through the image and see the background. I was wrong.
At first it was an all black background, but then I changed the transparent constructor to true on the buffer variable. Now it shows a white background (like the stage), but still no background image.

Answer 1

I'm not sure I completely understand the example, but it looks like the issue is that you're using copyPixels--this should replace the old pixels in the canvas bmp with new values.
Try using draw for the foreground instead:
canvas.copyPixels(background, bgRect, bgPoint);
canvas.draw(buffer, transform, null, null, clipRect);
Also, I'm not sure why you're drawing the background image to a different rect than the foreground? There may be something there.

Answer 2

I took a seperate movieclip and used it as a parallax behind the blitting tiles.