Forcing the recall of WM_PAINT - c++

Question

I've created a window using CreateWindowEx and that is working fine. The window opens.
In the function where I process messages, specifically WM_PAINT, I grab the cursor position using GetCursorPos and then draw a rectangle there. However, I would like the window to continuously update and redraw this rectangle, acting like a cursor.
I've created a thread like the following to try and force this:
DWORD WINAPI RedrawLoop(LPVOID lpParam) {
HWND handle = (HWND)lpParam;
while (true) {
RECT lpRect;
GetClientRect(handle, &lpRect);
InvalidateRect(handle, &lpRect, TRUE);
UpdateWindow(handle);
}
return 0;
}
However, this is not working. I've already checked that the handle passed in is the same as the window handle outside the thread.
I've also tried sending SendMessage(handle, WM_PAINT, 0, 0); and RedrawWindow(handle, NULL, NULL, 0); continuously with no luck.

Answer 1

First, you can get the current cursor position by processing the WM_MOUSEMOVE message and invalidate the current window.
Then draw a rectangle through the Rectangle function in the WM_PAINT message. (Note: The origin of coordinates is the upper left corner of the screen)
Here is the sample:
#include <Windows.h>
#include <commctrl.h>
LRESULT CALLBACK WndProc(HWND, UINT, WPARAM, LPARAM);
int WINAPI WinMain(HINSTANCE hInstance, HINSTANCE hPrevInstance, PSTR szCmdLine, int iCmdShow)
{
static TCHAR szAppName[] = TEXT("hello windows");
HWND hwnd;
MSG msg;
WNDCLASS wndclass;
wndclass.style = CS_HREDRAW | CS_VREDRAW;
wndclass.lpfnWndProc = WndProc;
wndclass.cbClsExtra = 0;
wndclass.cbWndExtra = 0;
wndclass.hInstance = hInstance;
wndclass.hIcon = LoadIcon(NULL, IDI_APPLICATION);
wndclass.hCursor = LoadCursor(NULL, IDC_ARROW);
wndclass.hbrBackground = (HBRUSH)GetStockObject(WHITE_BRUSH);
wndclass.lpszMenuName = NULL;
wndclass.lpszClassName = szAppName;
if (!RegisterClass(&wndclass))
{
MessageBox(NULL, TEXT("This program requires Windows NT!"), szAppName, MB_ICONERROR);
}
hwnd = CreateWindow(szAppName,
TEXT("the hello program"),
WS_OVERLAPPEDWINDOW,
CW_USEDEFAULT,
CW_USEDEFAULT,
CW_USEDEFAULT,
CW_USEDEFAULT,
NULL,
NULL,
hInstance,
NULL);
ShowWindow(hwnd, iCmdShow);
UpdateWindow(hwnd);
while (GetMessageW(&msg, NULL, 0, 0))
{
TranslateMessage(&msg);
DispatchMessageW(&msg);
}
return msg.wParam;
}
LRESULT CALLBACK WndProc(HWND hwnd, UINT message, WPARAM wParam, LPARAM lParam)
{
HDC hdc;
PAINTSTRUCT ps;
RECT rect;
static POINT pt;
switch (message)
{
case WM_CREATE:
{
}
case WM_MOUSEMOVE:
{
Sleep(100);
GetCursorPos(&pt);
InvalidateRect(hwnd, NULL, FALSE);
return 0;
}
case WM_PAINT:
hdc = BeginPaint(hwnd, &ps);
GetClientRect(hwnd, &rect);
Rectangle(hdc, pt.x-rect.right/4 , pt.y-rect.bottom/4, pt.x + rect.right / 4, pt.y + rect.bottom / 4);
EndPaint(hwnd, &ps);
return 0;
case WM_DESTROY:
PostQuitMessage(0);
return 0;
}
return DefWindowProc(hwnd, message, wParam, lParam);
}