Creating custom windows border edge disapears when resize smaller - c++

Question

Pretty much what the title says.
Im trying to make my own border, like that of visual studio 2015.
Once i have the border working like it should i will add a child window that is the main window for my program, the border will be the parent.
Will also try and add a outer glow once i get it working.
But the problem im having right now is, When i drag my border to resize it to make it smaller, The right or bottom start to get thinner depending on how fast i drag the mouse.
Is there a better way to do this or is there a simple step i can take to fix it.
#include <windows.h>
LPTSTR className_ = TEXT("BorderWindow");
BOOL WINAPI Init(HINSTANCE hInstance, INT cmdShow);
LRESULT CALLBACK WndProc(HWND hwnd, UINT message, WPARAM wparam, LPARAM lparam);
INT WINAPI wWinMain(HINSTANCE hInstance, HINSTANCE hPrevInstance, LPWSTR lpCmdLine, INT nCmdShow) {
MSG msg;
if (!Init(hInstance, nCmdShow)) {
return FALSE;
}
while (GetMessage(&msg, NULL, 0, 0)) {
TranslateMessage(&msg);
DispatchMessage(&msg);
}
return (INT)msg.wParam;
}
BOOL WINAPI Init(HINSTANCE hInstance, INT cmdShow)
{
WNDCLASSEX wcex{ 0 };
wcex.cbSize = sizeof(WNDCLASSEX);
wcex.style = 0;
wcex.lpfnWndProc = (WNDPROC)WndProc;
wcex.hInstance = hInstance;
wcex.hIcon = NULL;
wcex.hCursor = LoadCursor(nullptr, IDC_ARROW);
wcex.hbrBackground = (HBRUSH)(COLOR_HIGHLIGHT + 1);
wcex.lpszClassName = className_;
wcex.hIconSm = NULL;
if (!RegisterClassEx(&wcex)) {
return FALSE;
}
HWND hwnd_ = CreateWindow(className_, className_, WS_OVERLAPPEDWINDOW,
CW_USEDEFAULT, 0, 200, 500, nullptr, nullptr, hInstance, nullptr);
if (!hwnd_)
return FALSE;
ShowWindow(hwnd_, cmdShow);
UpdateWindow(hwnd_);
return TRUE;
}
void CreateHole(HWND hWnd)
{
HRGN WindowRgn;
HRGN HoleRgn;
//Get the window region:
RECT windowrect;
GetWindowRect(hWnd, &windowrect);
int width = windowrect.right - windowrect.left;
int height = windowrect.bottom - windowrect.top;
WindowRgn = CreateRectRgn(0, 0, width, height);
//Create the hole region:
HoleRgn = CreateRectRgn(2, 2, width - 2, height - 2);
CombineRgn(WindowRgn, WindowRgn, HoleRgn, RGN_DIFF);
SetWindowRgn(hWnd, WindowRgn, TRUE);
}
LRESULT CALLBACK WndProc(HWND hwnd, UINT message, WPARAM wparam, LPARAM lparam)
{
switch (message)
{
case WM_DESTROY:
PostQuitMessage(0);
return 0;
case WM_SIZE:
CreateHole(hwnd);
return 0;
case WM_NCCALCSIZE:
// remove default borders
return 0;
case WM_NCHITTEST:
{
RECT rc;
GetClientRect(hwnd, &rc);
POINT pt = { LOWORD(lparam), HIWORD(lparam) };
ScreenToClient(hwnd, &pt);
if (pt.y > (rc.bottom - 5))
{
if (pt.x > (rc.right - 5))
{
return HTBOTTOMRIGHT;
}
}
return HTBORDER;
}
}
return DefWindowProc(hwnd, message, wparam, lparam);
}

Answer 1

If you only need rectangular frame, an easier solution can be achieved as follows:
Window style should be such that normally the whole frame would be shown (WS_CAPTION|WS_POPUP works well for me).
Call DwmExtendFrameIntoClientArea() with MARGINS{0,0,0,1}.
Call SetWindowPos(nullptr, 0, 0, 0, 0, SWP_NOZORDER|SWP_NOOWNERZORDER|SWP_NOMOVE|SWP_NOSIZE|SWP_FRAMECHANGED) to recalculate NC area.
Return 0 from WM_NCCALCSIZE if wParam is TRUE. This has the effect of extending the client area to the window size including frame. The regular window frame will be removed, but shadow will still be drawn by DWM (see also remarks section of WM_NCCALCSIZE).
In WM_PAINT draw your frame and content area as you like but make sure to set opaque alpha channel for the margin defined by the DwmExtendFrameIntoClientArea() call. Otherwise part of regular frame would be visible in this area. You may use GDI+ for that as most regular GDI functions ignore alpha channel.
You can put child controls into this window, just as normal. Just make sure child controls don't overlap the margin defined by the DwmExtendFrameIntoClientArea() call because most GDI controls ignore the alpha channel.