c++中创建渐变背景

void __fastcall TForm1::FormPaint(TObject *Sender)
{
 Double d,c;
 d=this->ClientHeight/256;
 c=0;
 for (int i=0;i<255;i++)
 {
    Canvas->Brush->Color=0x100000000+i*10000;
    Canvas->FillRect(Rect(0,int(c+0.5),ClientWidth,c+d)) ;
    c=c+d;
 }
}