Re-learning gdi+[11]: DrawCurve

This example effect chart:

Code files:Unit Unit1;
Interface
Uses
Windows, Messages, sysutils, variants, Classes, Graphics, Controls, Forms,
Dialogs, Stdctrls, Comctrls, Extctrls;
Type
TForm1 = Class (Tform)
Button1:tbutton;
Trackbar1:ttrackbar;
Labelededit1:tlabelededit;
Labelededit2:tlabelededit;
Procedure Formmouseup (Sender:tobject; Button:tmousebutton;
Shift:tshiftstate; X, Y:integer);
Procedure Formpaint (Sender:tobject);
Procedure Formcreate (Sender:tobject);
Procedure Button1Click (Sender:tobject);
Procedure Trackbar1change (Sender:tobject);
Procedure Labelededit1change (Sender:tobject);
Procedure Labelededit2change (Sender:tobject);
End
Var
Form1:tform1;
Implementation
{$R *.DFM}
Uses Gdipobj, GDIPAPI;
Var
Ptarr:array of Tgppoint;
I:integer = 0;
Tension:single;
Procedure Tform1.formcreate (Sender:tobject);
Begin
Button1.caption: = ' erase ';
LabeledEdit1.EditLabel.Caption: = ' starting point ';
LabeledEdit2.EditLabel.Caption: = ' valid points ';
Labelededit1.text: = ' 0 ';
Labelededit2.text: = ' 0 ';
Trackbar1.showselrange: = False;
Trackbar1.min: =-25;
Trackbar1.max: = 35;
Trackbar1.position: = 5;
End
Procedure Tform1.formmouseup (Sender:tobject; Button:tmousebutton;
Shift:tshiftstate; X, Y:integer);
Begin
INC (i);
SetLength (Ptarr, i);
PTARR[I-1]. x: = x;
PTARR[I-1]. Y: = y;
Labelededit2.text: = IntToStr (i-1);
Text: = IntToStr (i);
Repaint;
End
Procedure Tform1.formpaint (Sender:tobject);
Var
G:tgpgraphics;
P:tgppen;
I,n1,n2:integer;
Begin
G: = Tgpgraphics.create (Canvas.handle);
P: = Tgppen.create (aclred, 2);
G.clear (Aclwhite);
N1: = Strtointdef (labelededit1.text, 0);
N2: = Strtointdef (Labelededit2.text, Length (Ptarr)-1);
{The following three parameters are optional, the default value for the last parameter is 0.5, and the 0 o'clock curve is converted to a straight line segment}
G.drawcurve (P, Pgppoint (Ptarr), Length (Ptarr), N1, N2, tension);
P.setwidth (1);
P.setcolor (Aclblack);
For I: = 0 to Length (ptarr)-1 do
G.drawellipse (P, ptarr[i]. X-2, Ptarr[i]. Y-2, 4, 4);
G.free;
P.free;
End
Procedure Tform1.labelededit1change (Sender:tobject);
Var
A,b:integer;
Begin
A: = Strtointdef (labelededit1.text, 0);
if (a < 0) or (A > Length (Ptarr)-2) Then
Labelededit1.text: = IntToStr (0);
A: = Strtointdef (labelededit1.text, 0);
B: = Strtointdef (labelededit2.text, 0);
If A+b > Length (Ptarr)-1 Then
Labelededit2.text: = IntToStr (Length (Ptarr) -1-a);
Repaint;
End
Procedure Tform1.labelededit2change (Sender:tobject);
Var
A,b:integer;
Begin
A: = Strtointdef (labelededit1.text, 0);
B: = Strtointdef (labelededit2.text, 0);
if (b < 0) or (b >= Length (Ptarr)-a) then
Labelededit2.text: = IntToStr (Length (Ptarr) -1-a);
Repaint;
End
Procedure Tform1.trackbar1change (Sender:tobject);
Begin
Tension: = TRACKBAR1.POSITION/10;
Repaint;
End
Procedure Tform1.button1click (Sender:tobject);
Begin
I: = 0;
SetLength (Ptarr, i);
Repaint;
Text: = IntToStr (i);
End
End.