Learn more about GDI + [72]: Region (1)-create Region

There are five ways to create a region for GDI +:

1. Create a rectangle (rectangular area );
2. Create a path;
3. It is created based on the handles of the GDI region;
4. Create a region based on the data obtained from the region;
5. No parameter is set.

This example demonstrates the first three methods.

In this example:

Code file:

Unit unit1; interfaceuses windows, messages, sysutils, variants, classes, graphics, controls, forms, dialogs, stdctrls, extctrls; Type tform1 = Class (tform) radiogroup1: tradiogroup; procedure formcreate (Sender: tobject); Procedure formpaint (Sender: tobject); Procedure radiogroup1click (Sender: tobject); end; var form1: tform1; implementation {$ R *. DFM} uses gdipobj, gdipapi; Procedure tform1.formcreate (Sender: tobject); begin radiogroup1.items. commatext: = 'rectangular channel, elliptical channel, polygon channel '; radiogroup1.itemindex: = 0; end; Procedure tform1.formpaint (Sender: tobject); var RT: tgprect; PTS: array [0 .. 2] of tpoint; rgnhandle: hrgn; G: tgpgraphics; Path: tgpgraphicspath; B: tgpbrush; RGN: tgpregion; begin RT: = makerect (20, 20,100, ClientHeight-40 ); PTS [0]: = point (RT. X + RT. width Div 2, Rt. y); PTS [1]: = point (RT. x, Rt. Y + RT. height); PTS [2]: = point (RT. X + RT. width, Rt. Y + RT. height); Case radiogroup1.itemindex of 0: RGN: = tgpregion. create (RT); {Based on the rectangle (rectangular area)} 1: begin {Based on the path} path: = tgpgraphicspath. create; Path. addellipse (RT); RGN: = tgpregion. create (PATH); Path. free; end; 2: begin {created based on the handle of the GDI region} rgnhandle: = createpolygonrgn (PTS, length (PTS), winding); RGN: = tgpregion. create (rgnhandle); deleteobject (rgnhandle); end; G: = tgpgraphics. create (canvas. handle); B: = tgphatchbrush. create (hatchstylediagonalcross, aclsilver, aclgray); G. fillregion (B, RGN); B. free; RGN. free; G. free; end; Procedure tform1.radiogroup1click (Sender: tobject); begin repaint; end.
 

Form file:

object Form1: TForm1  Left = 0  Top = 0  Caption = 'Form1'  ClientHeight = 137  ClientWidth = 238  Color = clBtnFace  Font.Charset = DEFAULT_CHARSET  Font.Color = clWindowText  Font.Height = -11  Font.Name = 'Tahoma'  Font.Style = []  OldCreateOrder = False  Position = poDesktopCenter  OnCreate = FormCreate  OnPaint = FormPaint  PixelsPerInch = 96  TextHeight = 13  object RadioGroup1: TRadioGroup    Left = 137    Top = 8    Width = 91    Height = 121    Caption = 'RadioGroup1'    TabOrder = 0    OnClick = RadioGroup1Click  endend