下面是一个简单的 blitting 示例：
private var m_bg:BitmapData = new BitmapData( 400, 300, false, 0xffff0000 ); // simple solid red colour
private var m_canvas:BitmapData = new BitmapData( 400, 300, true, 0x00000000 ); // the canvas that we're drawing into
private var m_obj:BitmapData = new BitmapData( 20, 20, false, 0xff00ff00 ); // simple green square
private var m_objDrawPos:Point = new Point; // where we'll draw our obj
private var m_objDir:Point = new Point; // the direction that our obj is moving in
private var m_objSpeed:Number = 20.0; // the speed of our obj
public function Main()
{
// create the bitmap for our canvas and add it to the stage
var b:Bitmap = new Bitmap( this.m_canvas );
this.addChild( b );
// set our initial direction
this.m_objDir.setTo( 1.0, 1.0 ); // diagonal right
// add our enter frame
this.addEventListener( Event.ENTER_FRAME, this._onEnterFrame );
}
private function _onEnterFrame( e:Event ):void
{
// move our object by changing it's draw position
this.m_objDrawPos.x += this.m_objDir.x * this.m_objSpeed;
this.m_objDrawPos.y += this.m_objDir.y * this.m_objSpeed;
// simple bounds change, to reflect the object
if ( this.m_objDrawPos.x < 0 || this.m_objDrawPos.x + this.m_obj.width > this.m_canvas.width )
this.m_objDir.x *= -1;
if ( this.m_objDrawPos.y < 0 || this.m_objDrawPos.y + this.m_obj.height > this.m_canvas.height )
this.m_objDir.y *= -1;
// copy our this.m_bg - this will erase all previous changes
// NOTE: depending on what your bg is, you can all use fillRect() if it's a solid colour
// NOTE: passing new Point() as the destPoint, will mean that our bg will always be drawn
// in the top-left of the canvas. As this never changes - you can keep this as a variable
this.m_canvas.copyPixels( this.m_bg, this.m_bg.rect, new Point );
// copy our object to its new position
this.m_canvas.copyPixels( this.m_obj, this.m_obj.rect, this.m_objDrawPos );
}
关于 blitting，您需要了解的是，作为 destPoint 传入的位置决定了您要进行 blitting 的 BitmapData 的左上角位置 - 将其视为 x 和 @普通DisplayObject 的987654325@ - (0,0) 表示绘制在左上角，而(canvas.width - obj.width, canvas.height - obj.height) 表示绘制在右下角。
为了让您的生活更轻松，请创建一个简单的类来为您存储所有这些数据。比如：
public class BlitObj
{
/************************************************************/
private var m_bmd:BitmapData = null; // our BitmapData graphics
private var m_offset:Point = null; // the offset (how we manage the reference point)
private var m_drawPos:Point = null; // our draw position for when we're blitting the object
private var m_position:Point = null; // the position of our object, in relation to the reference point
/************************************************************/
/**
* The position of the BlitObj, in relation to the reference point
*/
public function get position():Point { return this.m_position; }
/**
* The BitmapData graphics that we're going to blit
*/
public function get blitGraphics():BitmapData { return this.m_bmd; }
/**
* The position to blit this BlitObj at (top-left corner)
*/
public function get blitDestPos():Point { return this.m_drawPos; }
/************************************************************/
/**
* Creates a new BlitObj
* @param bmd The graphics for this BlitObj
* @param offset The offset to our registration point
*/
public function BlitObj( bmd:BitmapData, offset:Point = null )
{
this.m_bmd = bmd;
this.m_offset = ( offset == null ) ? new Point : offset;
this.m_drawPos = new Point( -this.m_offset.x, -this.m_offset.y );
this.m_position = new Point;
}
/**
* Sets the position of the BlitObj (in relation to its reference point)
* @param x The x position of the object
* @param y The y position of the object
*/
public function setPos( x:Number, y:Number ):void
{
this.m_position.setTo( x, y );
this.m_drawPos.setTo( x - this.m_offset.x, y - this.m_offset.y ) ;
}
}
blitting 时需要注意的一件事，这个类做的一件事，它处理offset。当您向copyPixels() 函数提供destPoint 时，它是在绘制之前放置BitmapData 左上角的位置。然而，通常你希望你的对象有一个与左上角不同的参考点（例如，一个圆的参考点在中间）。这可以让您处理。
// create our circle graphics with their registration point in the center
var circleBMD:BitmapData = ...; // get the graphics for your circle
var circle:BlitObj = new BlitObj( circleBMD, new Point( circleBMD.width * 0.5, circleBMD.height * 0.5 ) );
circle.setPos( this.stage.stageWidth * 0.5, this.stage.stageHeight * 0.5 ); // center it on the stage
// now you can draw it:
canvas.copyPixels( circle.blitGraphics, circle.blitGraphics.rect, circle.blitDestPos );