Форма с полупрозрачным фоном GDI+

#include <vcl.h>
#include <gdiplus.h>
#include <windows.h>
#pragma hdrstop
 
#include "Unit1.h"
//---------------------------------------------------------------------------
#pragma package(smart_init)
#pragma resource "*.dfm"
TForm1 *Form1;
using std::min;
using std::max;
Gdiplus::GdiplusStartupInput gdiplusStartupInput;
ULONG_PTR gdiplusToken;
AnsiString helpfile;
float z_min=0;
float z_max=0;
int x;
AnsiString FN="1.png";
Graphics::TBitmap *B=new Graphics::TBitmap;
//---------------------------------------------------------------------------
__fastcall TForm1::TForm1(TComponent* Owner)
    : TForm(Owner)
{
GdiplusStartup(& gdiplusToken,& gdiplusStartupInput, NULL);
float wo;
Form1->Image1->Align=alClient;
Form1->Image1->Picture->Assign(0);
WCHAR buff[10001];
Graphics::TBitmap *Buf = new Graphics::TBitmap();
Gdiplus::Image *image =new Gdiplus::Image (FN.WideChar(buff,10000));
Buf->Width=image->GetWidth();
Buf->Height=image->GetHeight();
Gdiplus::Graphics graphics(Buf->Canvas->Handle);
graphics.DrawImage(image, 0, 0, image->GetWidth(), image->GetHeight());
Form1->Image1->Picture->Assign(Buf);
delete image;
delete Buf;
}

#include <vcl.h>
#pragma hdrstop
#include "Unit1.h"
#pragma package(smart_init)
#pragma resource "*.dfm"
 
TForm1 *Form1;
BLENDFUNCTION blend;
SIZE s1;
TPoint p1;
 
void __fastcall Premult_BMP(TBitmap *BMP){
    Vcl::Imaging::Pngimage::TByteArray *dst;
    int x,y;
    Form1->Width = BMP->Width;
    Form1->Height = BMP->Height;
    assert(BMP->PixelFormat = pf32bit);
    for (y = 0; y < Form1->Height; y++){
        dst = (Vcl::Imaging::Pngimage::TByteArray *)BMP->ScanLine[y];
        for (x = 0; x < Form1->Width; x++){
            dst->data[x * 4] = dst->data[x * 4] * dst->data[x * 4 + 3] >> 8;
            dst->data[x * 4 + 1] = dst->data[x * 4 + 1] * dst->data[x * 4 + 3] >> 8;
            dst->data[x * 4 + 2] = dst->data[x * 4 + 2] * dst->data[x * 4 + 3] >> 8;
        };
    };
}
 
void __fastcall Load_BMP_From_PNG(TBitmap *BMP, String FileName){
    Vcl::Imaging::Pngimage::TByteArray *dst,*alpha;
    TRGBLine *src;
    int x,y;
    TPngImage *PNG = new TPngImage;
    PNG->LoadFromFile(FileName);
    BMP->PixelFormat = pf32bit;
    BMP->Width = PNG->Width;
    BMP->Height = PNG->Height;
    Form1->Width = PNG->Width;
    Form1->Height = PNG->Height;
    for (y = 0; y < Form1->Height; y++){
        alpha = PNG->AlphaScanline[y];
        src = (TRGBLine *)PNG->Scanline[y];
        dst = (Vcl::Imaging::Pngimage::TByteArray *)BMP->ScanLine[y];
        for (x = 0; x < Form1->Width; x++){
            dst->data[x * 4] = src->data[x].rgbtBlue;
            dst->data[x * 4 + 1] = src->data[x].rgbtGreen;
            dst->data[x * 4 + 2] = src->data[x].rgbtRed;
            dst->data[x * 4 + 3] = alpha->data[x];
        };
    };
    PNG->Free();
}
 
void __fastcall TForm1::FormCreate(TObject *Sender){
    TBitmap *Layer;
    TBitmap *Image1;
    TBitmap *Image2;
    TBitmap *Image3;
    blend.BlendOp = AC_SRC_OVER;
    blend.BlendFlags = 0;
    blend.SourceConstantAlpha = 255;
    blend.AlphaFormat = AC_SRC_ALPHA;
    s1.cx = Width;
    s1.cy = Height;
    p1 = Point(0,0);
    SetWindowLong(Handle, GWL_EXSTYLE, GetWindowLong(Handle, GWL_EXSTYLE) | WS_EX_LAYERED);
    Layer = new TBitmap;
    Layer->PixelFormat = pf32bit;
    Layer->Width = s1.cx;
    Layer->Height = s1.cy;
    Layer->Canvas->Brush->Color=RGB(0, 0, 0);
    Layer->Canvas->FillRect(Layer->Canvas->ClipRect);
    Image1 = new TBitmap;
    Load_BMP_From_PNG(Image1, "Image1.png");
    Premult_BMP(Image1);
    Image2 = new TBitmap;
    Load_BMP_From_PNG(Image2, "Image2.png");
    Premult_BMP(Image2);
    Image3 = new TBitmap;
    Load_BMP_From_PNG(Image3, "Image3.png");
    Premult_BMP(Image3);
    ::AlphaBlend(Layer->Canvas->Handle, 20, 20, Image1->Width, Image1->Height, Image1->Canvas->Handle, 0, 0, Image1->Width, Image1->Height, blend);
    ::AlphaBlend(Layer->Canvas->Handle, 50, 50, Image2->Width, Image2->Height, Image2->Canvas->Handle, 0, 0, Image2->Width, Image2->Height, blend);
    ::AlphaBlend(Layer->Canvas->Handle, 80, 80, Image3->Width, Image3->Height, Image3->Canvas->Handle, 0, 0, Image3->Width, Image3->Height, blend);
    Premult_BMP(Layer);
    UpdateLayeredWindow(Handle, 0, NULL, &s1, Layer->Canvas->Handle, &p1, 0, &blend, ULW_ALPHA);
    Image1->Free();
    Image2->Free();
    Image3->Free();
    Layer->Free();
    Show();
}