BGRABitmap tutorial 5

This tutorial shows you how to use layers.

Create a new project

Create a new project and add a reference to BGRABitmap, the same way as in the first tutorial.

Add a painting handler

With the object inspector, add an OnPaint handler and write : <delphi>procedure TForm1.FormPaint(Sender: TObject); var image: TBGRABitmap;

   size: single;

 procedure DrawMoon;
 var layer: TBGRABitmap;
 begin
   layer := TBGRABitmap.Create(image.Width,image.Height);
   layer.FillEllipseAntialias(layer.Width/2,layer.Height/2,size*0.4,size*0.4,BGRA(224,224,224,128));
   layer.EraseEllipseAntialias(layer.Width/2+size*0.15,layer.Height/2,size*0.3,size*0.3,255);
   image.PutImage(0,0,layer,dmDrawWithTransparency);
   layer.Free;
 end;

begin

 image := TBGRABitmap.Create(ClientWidth,ClientHeight);

 //Compute available space in both directions
 if image.Height < image.Width then
   size := image.Height
 else
   size := image.Width;

 image.GradientFill(0,0,image.Width,image.Height,
                    BGRA(128,192,255),BGRA(0,0,255),
                    gtLinear,PointF(0,0),PointF(0,image.Height),
                    dmSet);

 DrawMoon;

 image.Draw(Canvas,0,0,True);
 image.free;

end; </delphi>

The procedure creates an image and fill it with a blue gradient. This is the background layer.

The procedure DrawMoon creates a layer, draw a moon in it. First a white disk is drawn, then a smaller disk is substracted. Finally, this layer is merged with the background.

Run the program

You should see a blue sky with a moon. When you resize the form, the image is resized accordingly.

Previous tutorial (direct pixel access)