1 files changed, 36 insertions, 10 deletions

diff --git a/win32/PlatWin.cxx b/win32/PlatWin.cxx
index b1e08782d..0dd7cc549 100644
--- a/win32/PlatWin.cxx
+++ b/win32/PlatWin.cxx
@@ -243,12 +243,29 @@ void SetWindowPointer(HWND hWnd, void *ptr) noexcept {
 
 namespace {
 
+// system DPI, same for all monitor.
+UINT uSystemDPI = USER_DEFAULT_SCREEN_DPI;
+
 using GetDpiForWindowSig = UINT(WINAPI *)(HWND hwnd);
 GetDpiForWindowSig fnGetDpiForWindow = nullptr;
 
+using GetSystemMetricsForDpiSig = int(WINAPI *)(int nIndex, UINT dpi);
+GetSystemMetricsForDpiSig fnGetSystemMetricsForDpi = nullptr;
+
 void LoadDpiForWindow() noexcept {
 	HMODULE user32 = ::GetModuleHandleW(L"user32.dll");
 	fnGetDpiForWindow = DLLFunction<GetDpiForWindowSig>(user32, "GetDpiForWindow");
+	fnGetSystemMetricsForDpi = DLLFunction<GetSystemMetricsForDpiSig>(user32, "GetSystemMetricsForDpi");
+
+	using GetDpiForSystemSig = UINT(WINAPI *)(void);
+	GetDpiForSystemSig fnGetDpiForSystem = DLLFunction<GetDpiForSystemSig>(user32, "GetDpiForSystem");
+	if (fnGetDpiForSystem) {
+		uSystemDPI = fnGetDpiForSystem();
+	} else {
+		HDC hdcMeasure = ::CreateCompatibleDC({});
+		uSystemDPI = ::GetDeviceCaps(hdcMeasure, LOGPIXELSY);
+		::DeleteDC(hdcMeasure);
+	}
 }
 
 HINSTANCE hinstPlatformRes {};
@@ -427,10 +444,17 @@ UINT DpiForWindow(WindowID wid) noexcept {
 	if (fnGetDpiForWindow) {
 		return fnGetDpiForWindow(HwndFromWindowID(wid));
 	}
-	HDC hdcMeasure = ::CreateCompatibleDC({});
-	const UINT scale = ::GetDeviceCaps(hdcMeasure, LOGPIXELSY);
-	::DeleteDC(hdcMeasure);
-	return scale;
+	return uSystemDPI;
+}
+
+int SystemMetricsForDpi(int nIndex, UINT dpi) noexcept {
+	if (fnGetSystemMetricsForDpi) {
+		return fnGetSystemMetricsForDpi(nIndex, dpi);
+	}
+
+	int value = ::GetSystemMetrics(nIndex);
+	value = (dpi == uSystemDPI) ? value : ::MulDiv(value, dpi, uSystemDPI);
+	return value;
 }
 
 class SurfaceGDI : public Surface {
@@ -445,7 +469,7 @@ class SurfaceGDI : public Surface {
 	HBITMAP bitmap{};
 	HBITMAP bitmapOld{};
 
-	int logPixelsY = 72;
+	int logPixelsY = USER_DEFAULT_SCREEN_DPI;
 
 	int maxWidthMeasure = INT_MAX;
 	// There appears to be a 16 bit string length limit in GDI on NT.
@@ -1099,7 +1123,7 @@ SurfaceD2D::SurfaceD2D() noexcept :
 
 	pBrush = nullptr;
 
-	logPixelsY = 72;
+	logPixelsY = USER_DEFAULT_SCREEN_DPI;
 }
 
 SurfaceD2D::~SurfaceD2D() {
@@ -2370,6 +2394,7 @@ class ListBoxX : public ListBox {
 	unsigned int aveCharWidth;
 	Window *parent;
 	int ctrlID;
+	UINT dpi;
 	IListBoxDelegate *delegate;
 	const char *widestItem;
 	unsigned int maxCharWidth;
@@ -2405,7 +2430,7 @@ class ListBoxX : public ListBox {
 public:
 	ListBoxX() : lineHeight(10), fontCopy{}, technology(0), lb{}, unicodeMode(false),
 		desiredVisibleRows(9), maxItemCharacters(0), aveCharWidth(8),
-		parent(nullptr), ctrlID(0),
+		parent(nullptr), ctrlID(0), dpi(USER_DEFAULT_SCREEN_DPI),
 		delegate(nullptr),
 		widestItem(nullptr), maxCharWidth(1), resizeHit(0), wheelDelta(0) {
 	}
@@ -2462,6 +2487,7 @@ void ListBoxX::Create(Window &parent_, int ctrlID_, Point location_, int lineHei
 		hinstanceParent,
 		this);
 
+	dpi = DpiForWindow(wid);
 	POINT locationw = POINTFromPoint(location);
 	::MapWindowPoints(hwndParent, NULL, &locationw, 1);
 	location = PointFromPOINT(locationw);
@@ -2529,7 +2555,7 @@ PRectangle ListBoxX::GetDesiredRect() {
 
 	rcDesired.right = rcDesired.left + TextOffset() + width + (TextInset.x * 2);
 	if (Length() > rows)
-		rcDesired.right += ::GetSystemMetrics(SM_CXVSCROLL);
+		rcDesired.right += SystemMetricsForDpi(SM_CXVSCROLL, dpi);
 
 	AdjustWindowRect(&rcDesired);
 	return rcDesired;
@@ -2770,7 +2796,7 @@ POINT ListBoxX::MaxTrackSize() const {
 	PRectangle rc = PRectangle::FromInts(0, 0,
 		std::max(static_cast<unsigned int>(MinClientWidth()),
 		maxCharWidth * maxItemCharacters + static_cast<int>(TextInset.x) * 2 +
-		 TextOffset() + ::GetSystemMetrics(SM_CXVSCROLL)),
+		 TextOffset() + SystemMetricsForDpi(SM_CXVSCROLL, dpi)),
 		ItemHeight() * lti.Count());
 	AdjustWindowRect(&rc);
 	POINT ret = {static_cast<LONG>(rc.Width()), static_cast<LONG>(rc.Height())};
@@ -2879,7 +2905,7 @@ LRESULT ListBoxX::NcHitTest(WPARAM wParam, LPARAM lParam) const {
 	// window caption height + frame, even if one is hovering over the bottom edge of
 	// the frame, so workaround that here
 	if (hit >= HTTOP && hit <= HTTOPRIGHT) {
-		const int minHeight = GetSystemMetrics(SM_CYMINTRACK);
+		const int minHeight = SystemMetricsForDpi(SM_CYMINTRACK, dpi);
 		const int yPos = GET_Y_LPARAM(lParam);
 		if ((rc.Height() < minHeight) && (yPos > ((rc.top + rc.bottom)/2))) {
 			hit += HTBOTTOM - HTTOP;