问使用BitmapData的操作

EN

//store the movie's graphical content in a bitmapdata
var bmd:BitmapData = new BitmapData(movie.width, movie.height);
bmd.draw(movie);

//then create a temporary movie in which you will do the mirroring
var temp:MovieClip = new MovieClip();
temp.addChild(new Bitmap(bmd));

//create the diagonal mask
var _mask:MovieClip = new MovieClip();
with(_mask.graphics) beginFill(0xff0000), lineTo(movie.width, 0), lineTo(movie.width, movie.height), lineTo(0, 0), endFill();
temp.addChild(_mask);
temp.mask = _mask;
//this is the mirroring part
temp.scaleX = temp.scaleY = -1;
addChild(temp);

//then create another bitmapdata for storing the so called "upper-triangle"
//important, that this bitmapdata should be transparent, "true" sets this
var bmd1:BitmapData = new BitmapData(temp.width, temp.height, true, 0x00);
//then do another mirroring transformation
var matrix:Matrix = new Matrix(-1, 0, 0, -1);
matrix.tx = temp.width;
matrix.ty = temp.height;
//draw the visual content on the bitmapdata
bmd1.draw(temp, matrix);

//and finally, on the original bitmapdata, draw the mirrored part
bmd.draw(bmd1);

//and add it to the top layer of the original movie, or whatever you want to do with it
movie.addChild(new Bitmap(bmd));