operations with BitmapData

we have a square movie clip with some clild movie clips on it. Consider a diagonal of a squere. I want to make the following transform开发者_JAVA技巧ation with bimap data of a movie clip: the triangle located upper then diagonal should remain unchanged, the lower triangle should be replaced with simetric reflection of upper triangle.

Is there a simple way to do that?

Exactly, the way is to take a snapshot of the movie, then mirror it, take another snapshot and combine these two snapshots. Note, that the content you will get will be "static", so this way you can't copy the movieclip's animated parts.

//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));

The simplest way I can think of is rotating the movieclip 45º and draw the upper rectangle into the lower rectangle inversed, and then rotate the bitmapdata back 45º. You can use a Matrix (2nd argument in the BitmapData.draw method) to draw it rotated and not actually rotate anything.