BGRABitmap tutorial 3
This tutorial shows you how to draw on a bitmap with the mouse.
Create a new project
Create a new project and add a reference to BGRABitmap, the same way as in the first tutorial.
Create a new image
Add a private variable to the main form to store the image : <delphi> TForm1 = class(TForm)
private
{ private declarations }
image: TBGRABitmap;
public
{ public declarations }
end; </delphi>
Create the image when the form is created. To do this, double-click on the form, a procedure should appear in the code editor. Add the create instruction : <delphi>procedure TForm1.FormCreate(Sender: TObject); begin
image := TBGRABitmap.Create(640,480,BGRAWhite); //create a 640x480 image
end; </delphi>
Draw the bitmap
Add an OnPaint handler. To do this, select the main form, then go to the object inspector, in the event tab, and double-click on the OnPaint line. Then, add the drawing code : <delphi>procedure TForm1.FormPaint(Sender: TObject); begin
PaintImage;
end; </delphi>
Add the PaintImage procedure : <delphi>procedure TForm1.PaintImage; begin
image.Draw(Canvas,0,0,True);
end; </delphi>
After writing this, put the cursor on PaintImage and press Ctrl-Shift-C to add the declaration to the interface.
Handle mouse
With the object inspector, add handlers for MouseDown and MouseMove events : <delphi>procedure TForm1.FormMouseDown(Sender: TObject; Button: TMouseButton;
Shift: TShiftState; X, Y: Integer);
begin
if Button = mbLeft then DrawBrush(X,Y);
end;
procedure TForm1.FormMouseMove(Sender: TObject; Shift: TShiftState; X,
Y: Integer);
begin
if ssLeft in Shift then DrawBrush(X,Y);
end;</delphi>
Add the DrawBrush procedure : <delphi>procedure TForm1.DrawBrush(X, Y: Integer); const radius = 5; begin
image.GradientFill(X-radius,Y-radius, X+radius,Y+radius, BGRABlack,BGRAPixelTransparent, gtRadial, PointF(X,Y), PointF(X+5,Y), dmDrawWithTransparency);
PaintImage;
end;</delphi>
This procedure draws as radial gradient (gtRadial) :
- the bounding rectangle is (X-radius,Y-radius, X+radius,Y+radius).
- the center is black, the border is transparent
- the center is at (X,Y) and the border at (X+5,Y)
Run the program
You should be able to draw on the form.
