How to draw transparent with alpha transparency in Delphi? - image

Question

I want to draw quite complex images with alpha-transparent rectangles and alpha-transparent images.
There is GDI+ wrapper from Mitov, but it doesn't seem to support 32bit BMP files plus it rescales them and the documentation is terrible. BMPs are way faster than PNGs so I want to use them.
There is SynGDI wrapper of GDI+, but it seems very basic and there is no documentation for it.
There is also this trick for GDI:
procedure DrawAlphaAPI(Source: TBitmap; Destination: TCanvas;
const X, Y: Integer; const Opacity: Byte = 255);
var BlendFunc: TBlendFunction;
begin
BlendFunc.BlendOp := AC_SRC_OVER;
BlendFunc.BlendFlags := 0;
BlendFunc.SourceConstantAlpha := Opacity;
if Source.PixelFormat = pf32bit then
BlendFunc.AlphaFormat := AC_SRC_ALPHA
else
BlendFunc.AlphaFormat := 0;
Windows.AlphaBlend(Destination.Handle, X, Y, Source.Width, Source.Height,
Source.Canvas.Handle, 0, 0, Source.Width, Source.Height, BlendFunc);
end;
But when I call it with Opacity = 255 it draws 32bit bitmaps not properly (something like they are half transparent where they should be fully).
I don't want to use Scanline to make pixels transparent as this will be too complicated to draw all the transparent rectangles this way.
Also I thin GDI+ should be faster on modern computers, am I right?
So the question is: how to draw an alpha transparent rectangle and bitmap easily (without tons of code)?
Preferred Delphi: 7. I also have 2005 and XE3 but since 7 is a speed demon I would most want something to work from 7 up.

Answer 1

If you prepare the ordinary TBitmap, any of the GDI+ implementations can be used just assigning bmp.Canvas.Handle.
Your problem in compiling might be caused by an old DirctDraw-Version in the Folder, just remove it.
implementation
uses GDIPAPI, GDIPOBJ;
{$R *.dfm}
Procedure PrepareBMP(bmp: TBitmap; Width, Height: Integer);
var
p: Pointer;
begin
bmp.PixelFormat := pf32Bit;
bmp.Width := Width;
bmp.Height := Height;
bmp.HandleType := bmDIB;
bmp.ignorepalette := true;
bmp.alphaformat := afPremultiplied;
// clear all Scanlines
p := bmp.ScanLine[Height - 1];
ZeroMemory(p, Width * Height * 4);
end;
procedure TForm2.Button1Click(Sender: TObject);
var
bmp: TBitmap;
G: TGPGRaphics;
B: TGPSolidBrush;
begin
bmp := TBitmap.Create;
try
PrepareBMP(bmp, 300, 300);
G := TGPGRaphics.Create(bmp.Canvas.Handle);
B := TGPSolidBrush.Create(MakeColor(100, 255, 0, 0));
try
G.SetSmoothingMode(SmoothingModeHighQuality);
G.FillEllipse(B, MakeRect(0.0, 0, 300, 300));
B.SetColor(MakeColor(100, 0, 255, 128));
G.FillEllipse(B, MakeRect(40.0, 40, 260, 260));
finally
B.Free;
G.Free;
end;
// draw overlapping in Form Canvas to display transparency
Canvas.Draw(0, 0, bmp);
Canvas.Draw(100, 100, bmp);
finally
bmp.Free;
end;
end;