Problem on graphics.drawTriangle

I am trying to do Triangle Affine transform but having a trouble…


var vertices:Vector.<Number> = Vector.<Number>([10,10, 100,10, 10,100, 150,150]);
var indices:Vector.<int> = Vector.<int>([0,1,2, 1,3,2]);
var uvtData:Vector.<Number> = Vector.<Number>([0,0, 1,0, 0,1, 1,1]);

var shape:Shape = new Shape();
shape.graphics.beginBitmapFill(bitmap.bitmapData);
shape.graphics.drawTriangles(vertices, indices, uvtData);
shape.graphics.endFill();

var output:Bitmap = new Bitmap(new BitmapData(bitmap.width, bitmap.height));
output.bitmapData.draw(shape);

The result bitmap looks like:

My result bitmap keeps having overlayed images in it and I don’t know why it happens…
What is wrong in my code?