Hello all,
Here's the tutorial:
The tutorial is here[^]
I noticed that in the callback wndproc, LRESULT functions (are those functions?) were used to perform the tasks. Is there a specific reason why the author decided to do that as opposed to using void functions to do the drawing?
#include "stdafx.h"
#include "resource.h"
#define MAX_LOADSTRING 100
HINSTANCE hInst;
TCHAR szTitle[MAX_LOADSTRING];
TCHAR szWindowClass[MAX_LOADSTRING];
typedef struct tagShape
{
RECT rect;
UINT shapeID;
} Shape;
const UINT SHAPE_COUNT = 5;
Shape Shapes[SHAPE_COUNT];
UINT nCurrentIndex = 0;
bool isRubberBand = false;
POINT ptStart;
POINT ptCurrent;
ATOM MyRegisterClass(HINSTANCE hInstance);
BOOL InitInstance(HINSTANCE, int);
LRESULT CALLBACK WndProc(HWND, UINT, WPARAM, LPARAM);
LRESULT CALLBACK About(HWND, UINT, WPARAM, LPARAM);
int APIENTRY WinMain(HINSTANCE hInstance,
HINSTANCE hPrevInstance,
LPSTR lpCmdLine,
int nCmdShow)
{
MSG msg;
HACCEL hAccelTable;
LoadString(hInstance, IDS_APP_TITLE, szTitle, MAX_LOADSTRING);
LoadString(hInstance, IDC_PAINT_BEGINNER, szWindowClass, MAX_LOADSTRING);
WNDCLASSEX wcex;
wcex.cbSize = sizeof(WNDCLASSEX);
wcex.style = CS_HREDRAW | CS_VREDRAW;
wcex.lpfnWndProc = (WNDPROC)WndProc;
wcex.cbClsExtra = 0;
wcex.cbWndExtra = 0;
wcex.hInstance = hInstance;
wcex.hIcon = LoadIcon(hInstance, (LPCTSTR)IDI_PAINT_BEGINNER);
wcex.hCursor = LoadCursor(NULL, IDC_ARROW);
wcex.hbrBackground = (HBRUSH)(COLOR_WINDOW+1);
wcex.lpszMenuName = (LPCSTR)IDC_PAINT_BEGINNER;
wcex.lpszClassName = szWindowClass;
wcex.hIconSm = LoadIcon(wcex.hInstance, (LPCTSTR)IDI_SMALL);
RegisterClassEx(&wcex);
if (!InitInstance (hInstance, nCmdShow))
{
return FALSE;
}
hAccelTable = LoadAccelerators(hInstance, (LPCTSTR)IDC_PAINT_BEGINNER);
while (GetMessage(&msg, NULL, 0, 0))
{
if (!TranslateAccelerator(msg.hwnd, hAccelTable, &msg))
{
TranslateMessage(&msg);
DispatchMessage(&msg);
}
}
return msg.wParam;
}
BOOL InitInstance(HINSTANCE hInstance, int nCmdShow)
{
HWND hWnd;
hInst = hInstance;
memset(&Shapes, -1, sizeof(Shapes));
hWnd = CreateWindow(szWindowClass, szTitle, WS_OVERLAPPEDWINDOW,
CW_USEDEFAULT, 0, CW_USEDEFAULT, 0, NULL, NULL, hInstance, NULL);
if (!hWnd)
{
return FALSE;
}
ShowWindow(hWnd, nCmdShow);
UpdateWindow(hWnd);
return TRUE;
}
LRESULT OnCommand (HWND hWnd, int iID, int iEvent, HWND hWndControl, bool &isHandled);
LRESULT OnLButtonDown (HWND hWnd, UINT nCtrl, UINT x, UINT y);
LRESULT OnMouseMove (HWND hWnd, UINT nCtrl, UINT x, UINT y);
LRESULT OnLButtonUp (HWND hWnd, UINT nCtrl, UINT x, UINT y);
LRESULT OnPaint (HWND hWnd);
void DrawRubberBand(HWND hWnd);
LRESULT CALLBACK WndProc(HWND hWnd, UINT message, WPARAM wParam, LPARAM lParam)
{
switch (message)
{
case WM_CREATE:
{
HMENU hMenu = ::GetMenu(hWnd);
HMENU hMenuShapes = ::GetSubMenu(hMenu, 1);
::CheckMenuRadioItem(hMenuShapes, ID_SHAPE_RECTANGLE, ID_SHAPE_CIRCLE, ID_SHAPE_RECTANGLE, MF_BYCOMMAND);
}
case WM_COMMAND:
{
int wmId = LOWORD(wParam);
int wmEvent = HIWORD(wParam);
bool isHandled = true;
LRESULT lResult = OnCommand(hWnd, wmId, wmEvent, (HWND)lParam, isHandled);
if (!isHandled)
{
lResult = DefWindowProc(hWnd, message, wParam, lParam);
}
return lResult;
}
break;
case WM_CHAR:
{
if (VK_ESCAPE == wParam && isRubberBand)
{
isRubberBand = false;
DrawRubberBand(hWnd);
}
}
break;
case WM_LBUTTONDOWN:
{
return OnLButtonDown(hWnd, (UINT)wParam, LOWORD(lParam), HIWORD(lParam));
}
break;
case WM_MOUSEMOVE:
{
return OnMouseMove(hWnd, (UINT)wParam, LOWORD(lParam), HIWORD(lParam));
}
break;
case WM_LBUTTONUP:
{
return OnLButtonUp(hWnd, (UINT)wParam, LOWORD(lParam), HIWORD(lParam));
}
break;
case WM_PAINT:
{
return OnPaint(hWnd);
}
break;
case WM_DESTROY:
{
PostQuitMessage(0);
return 0;
}
break;
}
return DefWindowProc(hWnd, message, wParam, lParam);
}
LRESULT OnCommand (HWND hWnd, int iID, int iEvent, HWND hWndControl, bool &isHandled)
{
switch (iID)
{
case ID_SHAPE_RECTANGLE:
case ID_SHAPE_ELLIPSE:
{
HMENU hMenu = ::GetMenu(hWnd);
HMENU hMenuShapes = ::GetSubMenu(hMenu, 1);
::CheckMenuRadioItem(hMenuShapes, ID_SHAPE_RECTANGLE, ID_SHAPE_ELLIPSE, iID, MF_BYCOMMAND);
}
break;
case IDM_EXIT:
{
DestroyWindow(hWnd);
}
break;
default:
{
isHandled = false;
}
}
return 0;
}
LRESULT OnLButtonDown (HWND hWnd, UINT nCtrl, UINT x, UINT y)
{
ptStart.x = x;
ptStart.y = y;
isRubberBand = true;
ptCurrent.x = x;
ptCurrent.y = y;
DrawRubberBand(hWnd);
return 0;
}
LRESULT OnMouseMove (HWND hWnd, UINT nCtrl, UINT x, UINT y)
{
if (!isRubberBand)
{
return 0;
}
DrawRubberBand(hWnd);
ptCurrent.x = x;
ptCurrent.y = y;
DrawRubberBand(hWnd);
return 0;
}
LRESULT OnLButtonUp (HWND hWnd, UINT nCtrl, UINT x, UINT y)
{
if (!isRubberBand)
{
return 0;
}
DrawRubberBand(hWnd);
HMENU hMenu = ::GetMenu(hWnd);
HMENU hShapeMenu = ::GetSubMenu(hMenu, 1);
if (::GetMenuState(hShapeMenu, ID_SHAPE_RECTANGLE, MF_BYCOMMAND) & MF_CHECKED)
{
Shapes[nCurrentIndex].shapeID = ID_SHAPE_RECTANGLE;
}
else
{
Shapes[nCurrentIndex].shapeID = ID_SHAPE_ELLIPSE;
}
Shapes[nCurrentIndex].rect.left = ptStart.x;
Shapes[nCurrentIndex].rect.top = ptStart.y;
Shapes[nCurrentIndex].rect.right = ptCurrent.x;
Shapes[nCurrentIndex].rect.bottom = ptCurrent.y;
nCurrentIndex = (++nCurrentIndex)%SHAPE_COUNT;
isRubberBand = false;
InvalidateRect(hWnd, NULL, TRUE);
UpdateWindow(hWnd);
return 0;
}
LRESULT OnPaint (HWND hWnd)
{
PAINTSTRUCT ps;
HDC hdc;
hdc = ::BeginPaint(hWnd, &ps);
UINT index;
for (index = 0; index < SHAPE_COUNT; index++)
{
if (ID_SHAPE_RECTANGLE == Shapes[index].shapeID)
{
::Rectangle (
hdc,
Shapes[index].rect.left,
Shapes[index].rect.top,
Shapes[index].rect.right,
Shapes[index].rect.bottom
);
}
else
{
::Ellipse (
hdc,
Shapes[index].rect.left,
Shapes[index].rect.top,
Shapes[index].rect.right,
Shapes[index].rect.bottom
);
}
}
::EndPaint(hWnd, &ps);
return 0;
}
void DrawRubberBand(HWND hWnd)
{
HDC hdc;
hdc = ::GetDC(hWnd);
::SetROP2(hdc, R2_NOT);
::SelectObject(hdc, ::GetStockObject(NULL_BRUSH));
HMENU hMenu = ::GetMenu(hWnd);
HMENU hShapeMenu = ::GetSubMenu(hMenu, 1);
if (::GetMenuState(hShapeMenu, ID_SHAPE_RECTANGLE, MF_BYCOMMAND) & MF_CHECKED)
{
::Rectangle (
hdc,
ptStart.x,
ptStart.y,
ptCurrent.x,
ptCurrent.y
);
}
else
{
::Ellipse (
hdc,
ptStart.x,
ptStart.y,
ptCurrent.x,
ptCurrent.y
);
}
::ReleaseDC(hWnd, hdc);
}
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