BGRABitmap tutorial 7
This tutorial shows how to use splines.
Create a new project
Create a new project and add a reference to BGRABitmap, the same way as in the first tutorial.
Draw an opened spline
With the object inspector, add an OnPaint handler and write : <delphi>procedure TForm1.FormPaint(Sender: TObject); var
image: TBGRABitmap; pts: array of TPointF; storedSpline: array of TPointF; c: TBGRAPixel;
begin
image := TBGRABitmap.Create(ClientWidth,ClientHeight,ColorToBGRA(ColorToRGB(clBtnFace))); c := ColorToBGRA(ColorToRGB(clWindowText));
//rectangular polyline setlength(pts,4); pts[0] := PointF(50,50); pts[1] := PointF(150,50); pts[2] := PointF(150,150); pts[3] := PointF(50,150); image.DrawPolylineAntialias(pts,BGRA(255,0,0,150),1);
//compute spline points and draw as a polyline storedSpline := image.ComputeOpenedSpline(pts); image.DrawPolylineAntialias(storedSpline,c,1);
image.Draw(Canvas,0,0,True); image.free;
end;</delphi>
There are two lines that draw the spline. The first line computes the spline points, and the second draw them. Notice that it is a specific function for opened splines.
Draw a closed spline
Before image.Draw, add these lines : <delphi> for i := 0 to 3 do
pts[i].x += 200; image.DrawPolylineAntialias(pts,BGRA(255,0,0,150),1);
storedSpline := image.ComputeClosedSpline(pts); image.DrawPolygonAntialias(storedSpline,c,1);</delphi>
Go with the text cursor on the 'i' identifier and press Ctrl-Shift-C to add the variable declaration. The loop offsets the points to the right.
Two new lines draw a closed spline. Notice the specific function that computes closed splines and the call to DrawPolygonAntialias.
You can avoid using a variable to store spline points like this : <delphi>image.DrawPolygonAntialias(image.ComputeClosedSpline(pts),c,1);</delphi> However, if you do so, you cannot use the computed points more than once, they must be calculated each time you use them.
Run the program
This should draw a rectangle with a wide black pen.
