1.重载CreateParams函数，设置透明风格
2.然后重载它的WM_ERASEBKGND消息。
代码片段：
.h File
class TYourForm:public TForm
{
private:
void __fastcall WMNC(TMessage &Message);
public:
__fastcall TYourForm(TComponent *Owner);
BEGIN_MESSAGE_MAP
VCL_MESSAGE_HANDLER(WM_ERASEBKGND,TMessage,WMNC);
END_MESSAGE_MAP(TForm);
protected:
virtual void __fastcall CreateParams(TCreateParams &Params);
}
.cpp File
void __fastcall TYourForm::CreateParams(TCreateParams &Params)
{
TForm::CreateParams(Params);
Params.EX_STYLE=WS_EX_TRANSPARENT;
}
void __fastcall TYourForm::WMNC(TMessage &Message)
{
SetBkMode(GetWindowDC(this->Handle),OPAQUE);
ReleaseDC(this->Handle,GetWindowDC(this->Handle)) ;
Messgae.Result=1;
}