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win32 host: APPWINDOW client size used the system DPI, never read back #32

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Merged
defiantnerd merged 1 commit into from
Sep 16, 2026
Merged

win32 host: APPWINDOW client size used the system DPI, never read back #32

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28 changes: 28 additions & 0 deletions hosts/win32/widgets.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -2929,6 +2929,34 @@ namespace win32_host
);
// w.hwnd is set by AppWindowProc WM_NCCREATE; children created in WM_CREATE
if (w.hwnd) {
// The outer size above came from GetDpiForSystem(), which is only an
// estimate of where the frame will land: it may open on a monitor at a
// different scale (a 150% primary with a 100% secondary, or a remote
// session whose desktop DPI differs from the console's). Read the real
// per-monitor DPI back now that the HWND exists and, if it disagrees,
// redo the client -> outer conversion at that DPI.
//
// Without this the client area is wrong by the ratio of the two: a
// 940x400 request lands as a 1416x617 client when the system DPI is 144
// and the monitor is 96. WM_DPICHANGED does not cover it - that fires
// when a window MOVES between monitors, not when it is born on one that
// disagrees with the system DPI. Before ShowWindow so the correction is
// not visible as a resize flash. The crossplatform host does the same
// read-back in create_native_window.
UINT actual_dpi = GetDpiForWindow(w.hwnd);
if (actual_dpi && actual_dpi != initial_dpi) {
bool menu_row = false;
for (uint32_t ci = _widgets.child(index); ci != 0; ci = _widgets.next(ci))
if (_widgets.exists(ci) && _widgets[ci].hmenu != nullptr) { menu_row = true; break; }
RECT fix = { 0, 0,
LogicalToPhysical(w.width, actual_dpi),
LogicalToPhysical(w.height, actual_dpi) };
AdjustWindowRectExForDpi(&fix, style, menu_row ? TRUE : FALSE, ex_style, actual_dpi);
SetWindowPos(w.hwnd, nullptr, 0, 0,
fix.right - fix.left, fix.bottom - fix.top,
SWP_NOMOVE | SWP_NOZORDER | SWP_NOACTIVATE);
}

if (!is_plug) ApplyText(w.hwnd, w.text);
// Apply any icon attribute set before show.
if (w.attrs) {
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