Draw to TBitmap fail !

[Reference] http://qc.embarcadero.com/wc/qcmain.aspx?d=43018


At multi-thread program. The canvas handle of the Bitmap may be freed during the drawing procedure. So, lock the canvas before the drawing operation. And free after the drawing.
Lock the canvas may reduce the performance. But sometimes you have to do this.

Canvas->Lock();

drawing....

Canvas0->Unlock();