Correct way to repeatedly blit to window DC? - winapi

Question

I have put a procedure for capturing screenshots into memoryDC in a Winapi timer.
I can successfully blit the said image to the window, but how would i do this repeatedly, lets say every 1-2 seconds?
The currenct code i have can blit it 1-2 seconds at a time, but it wont blit it to the Window correctly (the image is misplaced).
How shall i go about doing this?
#include <windows.h>
#include <iostream>
#include <windowsx.h>
#define TIMERID 3232
/* Declare Windows procedure */
LRESULT CALLBACK WindowProcedure (HWND, UINT, WPARAM, LPARAM);
RECT rectangle{
50,
50,
690,
409
};
/* Make the class name into a global variable */
char szClassName[ ] = "CodeBlocksWindowsApp";
HDC handle_WindowDC;
HDC handle_MemoryDC;
HDC handle_ScreenDC;
//BITMAP bitmap;
HBITMAP handle_Bitmap;
int x, y;
HWND hand;
int WINAPI WinMain (HINSTANCE hThisInstance,
HINSTANCE hPrevInstance,
LPSTR lpszArgument,
int nCmdShow)
{
HWND hwnd; /* This is the handle for our window */
MSG messages; /* Here messages to the application are saved */
WNDCLASSEX wincl; /* Data structure for the windowclass */
/* The Window structure */
wincl.hInstance = hThisInstance;
wincl.lpszClassName = szClassName;
wincl.lpfnWndProc = WindowProcedure; /* This function is called by windows */
wincl.style = CS_DBLCLKS; /* Catch double-clicks */
wincl.cbSize = sizeof (WNDCLASSEX);
/* Use default icon and mouse-pointer */
wincl.hIcon = LoadIcon (NULL, IDI_APPLICATION);
wincl.hIconSm = LoadIcon (NULL, IDI_APPLICATION);
wincl.hCursor = LoadCursor (NULL, IDC_ARROW);
wincl.lpszMenuName = NULL; /* No menu */
wincl.cbClsExtra = 0; /* No extra bytes after the window class */
wincl.cbWndExtra = 0; /* structure or the window instance */
/* Use Windows's default colour as the background of the window */
wincl.hbrBackground = (HBRUSH) COLOR_BACKGROUND;
/* Register the window class, and if it fails quit the program */
if (!RegisterClassEx (&wincl))
return 0;
/* The class is registered, let's create the program*/
hwnd = CreateWindowEx (
0, /* Extended possibilites for variation */
szClassName, /* Classname */
"Code::Blocks Template Windows App", /* Title Text */
WS_OVERLAPPEDWINDOW, /* default window */
CW_USEDEFAULT, /* Windows decides the position */
CW_USEDEFAULT, /* where the window ends up on the screen */
1600, /* The programs width */
900, /* and height in pixels */
HWND_DESKTOP, /* The window is a child-window to desktop */
NULL, /* No menu */
hThisInstance, /* Program Instance handler */
NULL /* No Window Creation data */
);
/* Make the window visible on the screen */
ShowWindow (hwnd, nCmdShow);
SetTimer(hwnd, TIMERID, 1000, (TIMERPROC)NULL);
/* Run the message loop. It will run until GetMessage() returns 0 */
while (GetMessage (&messages, NULL, 0, 0))
{
/* Translate virtual-key messages into character messages */
TranslateMessage(&messages);
/* Send message to WindowProcedure */
DispatchMessage(&messages);
}
/* The program return-value is 0 - The value that PostQuitMessage() gave */
return messages.wParam;
}
/* This function is called by the Windows function DispatchMessage() */
LRESULT CALLBACK WindowProcedure (HWND hwnd, UINT message, WPARAM wParam, LPARAM lParam)
{
switch (message) /* handle the messages */
{
case WM_CREATE:{
}
//hand = CreateWindowEx(NULL, "STATIC", "", SS_BITMAP|WS_VISIBLE, 500,300, 640 ,360 , hwnd, HMENU(IDCSTATIC_BITMAP), GetModuleHandle(NULL), NULL); }
break;
case WM_TIMER:
switch(LOWORD(wParam)){
case TIMERID:{
//MessageBox(NULL,NULL,NULL,NULL);
handle_ScreenDC = GetDC(NULL);
handle_MemoryDC = CreateCompatibleDC(handle_ScreenDC);
x = GetDeviceCaps(handle_ScreenDC, HORZRES);
y = GetDeviceCaps(handle_ScreenDC, VERTRES);
handle_Bitmap = CreateCompatibleBitmap(handle_ScreenDC, 640, 360);
SelectObject(handle_MemoryDC, handle_Bitmap);
StretchBlt(handle_MemoryDC, 0, 0, 640, 360, handle_ScreenDC, 0, 0, x, y, SRCCOPY);
UpdateWindow(hwnd);
BitBlt(handle_WindowDC, 50, 50, x, y, handle_MemoryDC, 0, 0, SRCCOPY);
}
break;
}break;
case WM_PAINT:{
PAINTSTRUCT paintstruct;
handle_WindowDC = BeginPaint(hwnd, &paintstruct);
//BitBlt(handle_WindowDC, 50, 50, x, y, handle_MemoryDC, 0, 0, SRCCOPY);
EndPaint(hwnd, &paintstruct);
}
break;
case WM_DESTROY:
PostQuitMessage (0); /* send a WM_QUIT to the message queue */
break;
case WM_LBUTTONDOWN:{
std::cout <<"\nx: " << GET_X_LPARAM(lParam) << "\ny: " << GET_Y_LPARAM(lParam);
tagPOINT point;
point.x = GET_X_LPARAM(lParam);
point.y = GET_Y_LPARAM(lParam);
if( PtInRect(&rectangle, point)){
int x, y;
x = 2.5*(point.x - 50);
y = 2.5*(point.y - 50);
//I juse use setcursorpos for now, but when connecting to server.exe i will do a send() and send x,y coordinates along with
//a click or rightclick, or whatever.
SetCursorPos(x, y);
}
}
break;
default: /* for messages that we don't deal with */
return DefWindowProc (hwnd, message, wParam, lParam);
}
return 0;
}

Answer 1

You are using the DC from WM_PAINT to paint in the WM_TIMER code, that DC would have been released during EndPaint() -- the MSDN Docs says "EndPaint releases the display device context that BeginPaint retrieved'.
Also make sure you release your DCs with ReleaseDC(handle_ScreenDC) and DeleteObject(handle_MemoryDC).
The code for WM_TIMER should just invalidate the rectangle, do all The painting during WM_PAINT.
See this article for sample code.