Learn more about GDI + [11]: drawcurve-draw a curve

In this example:

Code File:

Unit unit1; interfaceuses windows, messages, sysutils, variants, classes, graphics, controls, forms, dialogs, stdctrls, comctrls, extctrls; Type tform1 = Class (tform) button1: tbutton; trackbar1: ttrackbar; tags: tlabelededit; labelededit2: tlabelededit; Procedure formmouseup (Sender: tobject; button: tmousebutton; shift: cursor; X, Y: integer); Procedure formpaint: tobject); Procedure future (Sender: tobject); Procedure trackbar1change (Sender: tobject); Procedure future (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: = 'start'; labelededit2.editlabel. caption: = 'valid point'; 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 of the last parameter is 0.5. When the value is 0, the 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 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: = strtointdef (labelededit1.text, 0); B: = strtointdef (labelededit2.text, 0); If (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.
 
   
 

Form file:

Object form1: tform1 left = 0 Top = 0 caption = 'form1' clientheight = 187 clientwidth = 264 color = clbtnface font. charset = default_charset font. color = clwindowtext font. height =-11 font. name = 'tahoma 'font. style = [] oldcreateorder = false position = pow.topcenter oncreate = formcreate onmouseup = formmouseup onpaint = formpaint pixelsperinch = 96 textheight = 13 object button1: tbutton left = 181 Top = 155 width = 75 Height = 25 caption = 'button1' taborder = 0 onclick = button1click end object trackbar1: ttrackbar left = 8 Top = 155 width = 167 Height = 25 taborder = 1 onchange = trackbar1change end object labelededit1: tlabelededit left = 208 Top = 54 width = 48 Height = 21 editlabel. width = 61 editlabel. height = 13 editlabel. caption = 'labelededit1' taborder = 2 onchange = labelededit1change end object labelededit2: tlabelededit left = 208 Top = 102 width = 48 Height = 21 editlabel. width = 61 editlabel. height = 13 editlabel. caption = 'labelededit2' taborder = 3 onchange = labelededit2change endend