Delphi下使用Windows GDI绘图

program Project1;

uses
  Winapi.Windows,
  Winapi.Messages, System.Classes;

function MyKeyDown(const Key : Integer): Boolean;
begin
  Result := GetAsyncKeyState(Key) <> 0;
end;

//callback fucntion
//process the messages
function MyWndProc(hW: HWnd; messages: UInt; wParams: WPARAM; lParams: LPARAM): LRESULT; stdcall;
var
  ps : PAINTSTRUCT;
  local_hdc : HDC;
begin
  Result := 0;
  case messages of
    WM_COMMAND:
    begin

    end;

    WM_PAINT:
    begin
      local_hdc := BeginPaint(hW, ps);
      EndPaint(hW, ps);
    end;

    WM_DESTROY:
    begin
      PostQuitMessage(0);
    end
  else
    Result := DefWindowProc(hW, messages, wParams, lParams);
  end;
end;

function MyRegisterClass(hInst : HINST): WORD;
var
  wclass: TWndClassExW;
begin
  //Don't forget to set all the properties, or you will failed to register
  //you can use Structure 'TWndClassW' and register with function 'RegisterClassW'
  wclass.cbSize := SizeOf(WNDCLASSEXW);                                 //set size of this structure
  wclass.style := CS_HREDRAW or CS_VREDRAW;                             //set style of general property of this form
  wclass.lpfnWndProc := @MyWndProc;                                     //callback function
  wclass.cbClsExtra := 0;
  wclass.cbWndExtra := 0;
  wclass.hInstance := hInst;                                           //set instance
  wclass.hIcon := LoadIcon(0, IDI_APPLICATION);
  wclass.hCursor := LoadCursor(0, IDC_ARROW);
  wclass.hbrBackground := GetStockObject(WHITE_BRUSH);
  wclass.lpszMenuName := nil;
  wclass.lpszClassName := 'Project';
  wclass.hIconSm := LoadIcon(wclass.hInstance, MAKEINTRESOURCE(0));   //set small icon

  Result := RegisterClassExW(wclass);
end;

var
  gbl_hW : HWND;

function InitInstance(hInst : HINST; nCmdShow : Integer): Boolean;
var
  hW : HWND;
begin
  Result := False;

  hW := CreateWindowW('Project', 'ProjectOne', WS_OVERLAPPEDWINDOW,
      CW_USEDEFAULT, 0, CW_USEDEFAULT, 0, 0, 0, hInst, nil);

  if hW <> 0 then
  begin
    ShowWindow(hW, nCmdShow);
    UpdateWindow(hW);
    gbl_hW := hW;
    Result := True;
  end;
end;

{$R *.res}

var
  gbl_hInstance : HINST;
  gbl_msg : MSG;
  gbl_hdc : HDC;

var
  win_Rect : TRect;
  i, x, y : Integer;
  color : COLORREF;

var
  red_Pen : HPEN;
  red_Soild_Brush : HBRUSH;
  blue_Hatched_Brush : HBRUSH;
  sideLen : Integer;
  iRect : TRect;

begin

  gbl_hInstance := GetModuleHandle(nil);

  //you can also use global variables HInstance in DELPHI
  //HInstance will be initialized in procedure _InitExe(see it in the unit SysInit)
  //like: if RegisterClass(HInstance) = 0 then
  if MyRegisterClass(gbl_hInstance) = 0 then
  begin
    MessageBox(0, 'RegisterClass Error', 'Error', MB_OKCANCEL);
    Exit;
  end;

  if not InitInstance(gbl_hInstance, SW_SHOW) then
  begin
    MessageBox(0, 'InitInstance Error', 'Error', MB_OKCANCEL);
    Exit;
  end;

  //get graphics device context
  gbl_hdc := GetDC(gbl_hW);

  //create a pen with solid style and red color, one pixel wide
  red_Pen := CreatePen(PS_SOLID, 1, RGB(255, 0, 0));

  //select then pen into device context
  SelectObject(gbl_hdc, red_Pen);

  //two ways to create brush
  //solid brush
  red_Soild_Brush := CreateSolidBrush(RGB(255, 0, 0));
  //hatched brush with vertical shadow line
  blue_Hatched_Brush := CreateHatchBrush(HS_VERTICAL, RGB(0, 255, 0));

  SelectObject(gbl_hdc, red_Soild_Brush);

  //get size of form
  GetWindowRect(gbl_hW, win_Rect);

  Randomize;

  //GetMessage will be wait a msg
  while GetMessage(gbl_msg, 0, 0, 0) do
  begin
    TranslateMessage(gbl_msg);
    DispatchMessage(gbl_msg);

    if MyKeyDown(VK_ESCAPE) then
      SendMessage(gbl_hW, WM_CLOSE, 0, 0);

    for i := 0 to 100 do
    begin
      x := Random(1000) * (win_Rect.Right - win_Rect.Left) div 1000;
      y := Random(1000) * (win_Rect.Bottom - win_Rect.Top) div 1000;
      color := RGB(Random(1000) mod 255, Random(1000) mod 255, Random(1000) mod 255);

      //plot a pixel
      SetPixel(gbl_hdc, x, y, color);
    end;

    //plot a triangle
    sideLen := Random(20);
    MoveToEx(gbl_hdc, x, y, nil);
    LineTo(gbl_hdc, x + sideLen, y - sideLen);
    LineTo(gbl_hdc, x - sideLen, y - sideLen);
    LineTo(gbl_hdc, x, y);

    //plot a rectangle
    sideLen := Random(30);
    //plot a Solid rectangle
    //Rectangle(gbl_hdc, x, y, x + sideLen, y + sideLen);

    iRect := Rect(x, y, x + 100, y + 100);
    //fill a Solid rectangle
    //FillRect(gbl_hdc, iRect, red_Soild_Brush);

    //draw a rect with brush
    //notice we use HS_VERTICAL style,
    //you might not be able to see the rectangle
    FrameRect(gbl_hdc, iRect, blue_Hatched_Brush);
    //or use temporary variable
    FrameRect(gbl_hdc, iRect, CreateHatchBrush(HS_VERTICAL, RGB(0, 0, 255)));
  end;

  //destroy
  DeleteObject(red_Pen);
  DeleteObject(red_Soild_Brush);
  ReleaseDC(gbl_hW, gbl_hdc);

  //if you want to keep drawing all the time without
  //do other operations to send message to queue,
  //use while true with function PeekMessage
  //see difference between 'GetMessage()' and 'PeekMessage()'

end.

一些简单的注解都用英文写在代码里，边学好英语边学撸代码，不会的API看MSDN Helper，养成一个好习惯。

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