MinimalDpiTest

main.cpp

#include <iostream>

#undef _WIN32_WINNT
#define _WIN32_WINNT 0x0603
#define WM_DPICHANGED 0x02E0
#include <shellscalingapi.h>

#define WIN32_LEAN_AND_MEAN
#include <windows.h>

HINSTANCE hInst;
float dpiScale = 1.f;
int wndPos = 100;
int wndSize = 500;

ATOM MyRegisterClass(HINSTANCE hInstance);
BOOL InitInstance(HINSTANCE, int);
LRESULT CALLBACK WndProc(HWND, UINT, WPARAM, LPARAM);
int APIENTRY _tWinMain(_In_ HINSTANCE hInstance, _In_opt_ HINSTANCE, _In_ LPTSTR, _In_ int nCmdShow);

int main() {
    return _tWinMain(GetModuleHandle(NULL), NULL, GetCommandLine(), SW_SHOW);
}

int APIENTRY _tWinMain(_In_ HINSTANCE hInstance, _In_opt_ HINSTANCE, _In_ LPTSTR, _In_ int nCmdShow)
{
	::SetProcessDpiAwareness(PROCESS_PER_MONITOR_DPI_AWARE);

	MyRegisterClass(hInstance);

	InitInstance(hInstance, nCmdShow);

	MSG msg;
	while (::GetMessage(&msg, NULL, 0, 0))
	{
		::TranslateMessage(&msg);
		::DispatchMessage(&msg);
	}

	return (int) msg.wParam;
}

ATOM MyRegisterClass(HINSTANCE hInstance)
{
	WNDCLASSEX wcex;

	wcex.cbSize = sizeof(WNDCLASSEX);

	wcex.style			= CS_HREDRAW | CS_VREDRAW;
	wcex.lpfnWndProc	= WndProc;
	wcex.cbClsExtra		= 0;
	wcex.cbWndExtra		= 0;
	wcex.hInstance		= hInstance;
	wcex.hIcon			= NULL;
	wcex.hCursor		= NULL;
	wcex.hbrBackground	= (HBRUSH)(COLOR_WINDOW+1);
	wcex.lpszMenuName	= NULL;
	wcex.lpszClassName	= L"DpiTest";
	wcex.hIconSm		= NULL;

	return RegisterClassEx(&wcex);
}

BOOL InitInstance(HINSTANCE hInstance, int nCmdShow)
{
	HWND hWnd;

	hInst = hInstance;

	RECT r;
	r.left = wndPos;
	r.top = wndPos;
	r.right = r.left + wndSize;
	r.bottom = r.top + wndSize;

	const auto mon = ::MonitorFromRect(&r, MONITOR_DEFAULTTOPRIMARY);
	UINT dpi_x = 0;
	UINT dpi_y = 0;
	::GetDpiForMonitor(mon, MDT_DEFAULT, &dpi_x, &dpi_y);
	dpiScale = dpi_x / 96.f;

	hWnd = ::CreateWindow(
		L"DpiTest",
		L"",
		WS_OVERLAPPEDWINDOW,
		wndPos,
		wndPos,
		wndSize * dpiScale,
		wndSize * dpiScale,
		NULL,
		NULL,
		hInstance,
		NULL
	);

	ShowWindow(hWnd, nCmdShow);
	UpdateWindow(hWnd);

	return TRUE;
}

LRESULT CALLBACK WndProc(HWND hWnd, UINT message, WPARAM wParam, LPARAM lParam)
{
	switch (message)
	{
		case WM_DPICHANGED:
		{
			int dpi_x = LOWORD(wParam);
			int dpi_y = HIWORD(wParam);
			dpiScale = dpi_x / 96.f;
			RECT rect = *(RECT *)lParam;
			::SetWindowPos(hWnd, 0, rect.left, rect.top, rect.right - rect.left, rect.bottom - rect.top, SWP_NOZORDER);
			break;
		}

		case WM_GETMINMAXINFO:
		{
			MINMAXINFO* info = (MINMAXINFO*)lParam;
			info->ptMinTrackSize.x = wndSize * dpiScale;
			info->ptMinTrackSize.y = wndSize * dpiScale;
			break;
		}

		case WM_SIZE:
		{
			RECT r;
			::GetWindowRect(hWnd, &r);
			int width = (r.right - r.left);
			int height = (r.bottom - r.top);
			std::cout << "WM_SIZE " << width << " " << height << " scale factor: " << (1.f * width / wndSize) << std::endl;
			break;
		}

		case WM_WINDOWPOSCHANGED:
		{
			WINDOWPOS* pos = (WINDOWPOS*)lParam;
			std::cout << "WM_WINDOWPOSCHANGED " << pos->x << " " << pos->y << " " << pos->cx << " " << pos->cy << std::endl;
			return DefWindowProc(hWnd, message, wParam, lParam);
		}

		case WM_DESTROY:
			PostQuitMessage(0);
			break;

		default:
			return DefWindowProc(hWnd, message, wParam, lParam);
	}
}

MinimalDpiTest.sln

Microsoft Visual Studio Solution File, Format Version 12.00
# Visual Studio 2012
Project("{8BC9CEB8-8B4A-11D0-8D11-00A0C91BC942}") = "MinimalDpiTest", "MinimalDpiTest\MinimalDpiTest.vcxproj", "{BFC3A0A7-3FF0-4056-B46E-BF9418C7278D}"
EndProject
Global
	GlobalSection(SolutionConfigurationPlatforms) = preSolution
		Debug|Win32 = Debug|Win32
		Release|Win32 = Release|Win32
	EndGlobalSection
	GlobalSection(ProjectConfigurationPlatforms) = postSolution
		{BFC3A0A7-3FF0-4056-B46E-BF9418C7278D}.Debug|Win32.ActiveCfg = Debug|Win32
		{BFC3A0A7-3FF0-4056-B46E-BF9418C7278D}.Debug|Win32.Build.0 = Debug|Win32
		{BFC3A0A7-3FF0-4056-B46E-BF9418C7278D}.Release|Win32.ActiveCfg = Release|Win32
		{BFC3A0A7-3FF0-4056-B46E-BF9418C7278D}.Release|Win32.Build.0 = Release|Win32
	EndGlobalSection
	GlobalSection(SolutionProperties) = preSolution
		HideSolutionNode = FALSE
	EndGlobalSection
EndGlobal

MinimalDpiTest.vcxproj

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