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fix: use default behaviour for dpi changed on windows. #14336

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fix: use default behaviour for dpi changed on windows. #14336

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7a3e14e
fix: use default behaviour for dpi changed.
thegoodtgg Oct 27, 2025
7659c68
fix: update min and max size while dpi changed.
thegoodtgg Oct 29, 2025
1fed384
fix: store dpi in SDL_WindowData.
thegoodtgg Oct 29, 2025
59cd016
fix: ci.
thegoodtgg Oct 29, 2025
2e19a5b
fix: ci.
thegoodtgg Oct 29, 2025
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116 changes: 46 additions & 70 deletions src/video/windows/SDL_windowsevents.c
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Original file line number Diff line number Diff line change
Expand Up @@ -1146,6 +1146,24 @@ static bool DispatchModalLoopMessageHook(HWND *hwnd, UINT *msg, WPARAM *wParam,
return false;
}

static void WIN_OnDPIUpdateMinMaxSize(SDL_Window *window, int old_dpi, int new_dpi)
{
float scale = (float)new_dpi / old_dpi;

if (window->min_w || window->min_h)
{
int new_min_w = (int)SDL_ceilf(window->min_w * scale);
int new_min_h = (int)SDL_ceilf(window->min_h * scale);
SDL_SetWindowMinimumSize(window, new_min_w, new_min_h);
}
if (window->max_w || window->max_h)
{
int new_max_w = (int)SDL_ceilf(window->max_w * scale);
int new_max_h = (int)SDL_ceilf(window->max_h * scale);
SDL_SetWindowMaximumSize(window, new_max_w, new_max_h);
}
}

LRESULT CALLBACK WIN_WindowProc(HWND hwnd, UINT msg, WPARAM wParam, LPARAM lParam)
{
SDL_WindowData *data;
Expand Down Expand Up @@ -1669,7 +1687,7 @@ LRESULT CALLBACK WIN_WindowProc(HWND hwnd, UINT msg, WPARAM wParam, LPARAM lPara
w = size.right - size.left;
h = size.bottom - size.top;
#ifdef HIGHDPI_DEBUG
SDL_Log("WM_GETMINMAXINFO: max window size: %dx%d using dpi: %u", w, h, dpi);
// SDL_Log("WM_GETMINMAXINFO: max window size: %dx%d using dpi: %u", w, h, dpi);
#endif
}

Expand Down Expand Up @@ -1706,7 +1724,11 @@ LRESULT CALLBACK WIN_WindowProc(HWND hwnd, UINT msg, WPARAM wParam, LPARAM lPara
#endif // WM_GETMINMAXINFO

case WM_WINDOWPOSCHANGING:

{
#ifdef WMMSG_DEBUG
const WINDOWPOS *windowpos = (WINDOWPOS *)lParam;
SDL_Log("WM_WINDOWPOSCHANGING: output size: (%dx%d)", windowpos->cx, windowpos->cy);
#endif // !WMMSG_DEBUG
if (data->expected_resize) {
returnCode = 0;
} else if (data->in_modal_loop) {
Expand All @@ -1726,6 +1748,7 @@ LRESULT CALLBACK WIN_WindowProc(HWND hwnd, UINT msg, WPARAM wParam, LPARAM lPara
returnCode = 0;
}
break;
}

case WM_WINDOWPOSCHANGED:
{
Expand All @@ -1737,7 +1760,11 @@ LRESULT CALLBACK WIN_WindowProc(HWND hwnd, UINT msg, WPARAM wParam, LPARAM lPara
RECT rect;
int x, y;
int w, h;

#ifdef WMMSG_DEBUG
GetClientRect(hwnd, &rect);
SDL_Log("WM_WINDOWPOSCHANGED: output size: WINDOWPOS(%dx%d), ClientRect(%d,%d)", windowpos->cx, windowpos->cy,
rect.right, rect.bottom);
#endif // !WMMSG_DEBUG
if (windowpos->flags & SWP_SHOWWINDOW) {
SDL_SendWindowEvent(data->window, SDL_EVENT_WINDOW_SHOWN, 0, 0);
}
Expand Down Expand Up @@ -2291,70 +2318,6 @@ LRESULT CALLBACK WIN_WindowProc(HWND hwnd, UINT msg, WPARAM wParam, LPARAM lPara
} break;

case WM_GETDPISCALEDSIZE:
// Windows 10 Creators Update+
/* Documented as only being sent to windows that are per-monitor V2 DPI aware.

Experimentation shows it's only sent during interactive dragging, not in response to
SetWindowPos. */
if (data->videodata->GetDpiForWindow && data->videodata->AdjustWindowRectExForDpi) {
/* Windows expects applications to scale their window rects linearly
when dragging between monitors with different DPI's.
e.g. a 100x100 window dragged to a 200% scaled monitor
becomes 200x200.

For SDL, we instead want the client size to scale linearly.
This is not the same as the window rect scaling linearly,
because Windows doesn't scale the non-client area (titlebar etc.)
linearly. So, we need to handle this message to request custom
scaling. */

const int nextDPI = (int)wParam;
const int prevDPI = (int)data->videodata->GetDpiForWindow(hwnd);
SIZE *sizeInOut = (SIZE *)lParam;

int frame_w, frame_h;
int query_client_w_win, query_client_h_win;

#ifdef HIGHDPI_DEBUG
SDL_Log("WM_GETDPISCALEDSIZE: current DPI: %d potential DPI: %d input size: (%dx%d)",
prevDPI, nextDPI, sizeInOut->cx, sizeInOut->cy);
#endif

// Subtract the window frame size that would have been used at prevDPI
{
RECT rect = { 0 };

if (!(data->window->flags & SDL_WINDOW_BORDERLESS) && !SDL_WINDOW_IS_POPUP(data->window)) {
WIN_AdjustWindowRectForHWND(hwnd, &rect, prevDPI);
}

frame_w = -rect.left + rect.right;
frame_h = -rect.top + rect.bottom;

query_client_w_win = sizeInOut->cx - frame_w;
query_client_h_win = sizeInOut->cy - frame_h;
}

// Add the window frame size that would be used at nextDPI
{
RECT rect = { 0 };
rect.right = query_client_w_win;
rect.bottom = query_client_h_win;

if (!(data->window->flags & SDL_WINDOW_BORDERLESS) && !SDL_WINDOW_IS_POPUP(data->window)) {
WIN_AdjustWindowRectForHWND(hwnd, &rect, nextDPI);
}

// This is supposed to control the suggested rect param of WM_DPICHANGED
sizeInOut->cx = rect.right - rect.left;
sizeInOut->cy = rect.bottom - rect.top;
}

#ifdef HIGHDPI_DEBUG
SDL_Log("WM_GETDPISCALEDSIZE: output size: (%dx%d)", sizeInOut->cx, sizeInOut->cy);
#endif
return TRUE;
}
break;

case WM_DPICHANGED:
Expand All @@ -2363,7 +2326,6 @@ LRESULT CALLBACK WIN_WindowProc(HWND hwnd, UINT msg, WPARAM wParam, LPARAM lPara
const int newDPI = HIWORD(wParam);
RECT *const suggestedRect = (RECT *)lParam;
int w, h;

#ifdef HIGHDPI_DEBUG
SDL_Log("WM_DPICHANGED: to %d\tsuggested rect: (%d, %d), (%dx%d)", newDPI,
suggestedRect->left, suggestedRect->top, suggestedRect->right - suggestedRect->left, suggestedRect->bottom - suggestedRect->top);
Expand All @@ -2378,11 +2340,15 @@ LRESULT CALLBACK WIN_WindowProc(HWND hwnd, UINT msg, WPARAM wParam, LPARAM lPara
#endif
return 0;
}
// Update minimum size and maximum size for new dpi
const int prevDPI = data->dpi;
WIN_OnDPIUpdateMinMaxSize(data->window, prevDPI, newDPI);

// Interactive user-initiated resizing/movement
{
/* Calculate the new frame w/h such that
the client area size is maintained. */

RECT rect = { 0 };
rect.right = data->window->w;
rect.bottom = data->window->h;
Expand All @@ -2391,8 +2357,10 @@ LRESULT CALLBACK WIN_WindowProc(HWND hwnd, UINT msg, WPARAM wParam, LPARAM lPara
WIN_AdjustWindowRectForHWND(hwnd, &rect, newDPI);
}

w = rect.right - rect.left;
h = rect.bottom - rect.top;
// w = rect.right - rect.left;
// h = rect.bottom - rect.top;
w = suggestedRect->right - suggestedRect->left;
h = suggestedRect->bottom - suggestedRect->top;
}

#ifdef HIGHDPI_DEBUG
Expand All @@ -2410,6 +2378,7 @@ LRESULT CALLBACK WIN_WindowProc(HWND hwnd, UINT msg, WPARAM wParam, LPARAM lPara
h,
SWP_NOZORDER | SWP_NOACTIVATE);
data->expected_resize = false;
data->dpi = newDPI;
return 0;
}
break;
Expand Down Expand Up @@ -2446,6 +2415,13 @@ LRESULT CALLBACK WIN_WindowProc(HWND hwnd, UINT msg, WPARAM wParam, LPARAM lPara
} else if (returnCode >= 0) {
return returnCode;
} else {
#ifdef WMMSG_DEBUG
if (msg > MAX_WMMSG) {
SDL_Log("Forwarding UNKNOWN (%d) to DefWindowProc", msg);
} else {
SDL_Log("Forwarding %s to DefWindowProc", wmtab[msg]);
}
#endif // !WMMSG_DEBUG
return CallWindowProc(DefWindowProc, hwnd, msg, wParam, lParam);
}
}
Expand Down
6 changes: 6 additions & 0 deletions src/video/windows/SDL_windowswindow.c
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Original file line number Diff line number Diff line change
Expand Up @@ -392,6 +392,7 @@ static bool SetupWindowData(SDL_VideoDevice *_this, SDL_Window *window, HWND hwn
data->videodata = videodata;
data->initializing = true;
data->hint_erase_background_mode = GetEraseBackgroundModeHint();
data->dpi = _this->internal->GetDpiForWindow(hwnd);


// WIN_WarpCursor() jitters by +1, and remote desktop warp wobble is +/- 1
Expand Down Expand Up @@ -2296,4 +2297,9 @@ bool WIN_SetWindowModal(SDL_VideoDevice *_this, SDL_Window *window, bool modal)
return true;
}

int WIN_GetWindowDpi(SDL_VideoDevice *_this, SDL_Window *window)
{
return window->internal->dpi;
}

#endif // SDL_VIDEO_DRIVER_WINDOWS
2 changes: 2 additions & 0 deletions src/video/windows/SDL_windowswindow.h
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Original file line number Diff line number Diff line change
Expand Up @@ -104,6 +104,7 @@ struct SDL_WindowData
// Whether we retain the content of the window when changing state
UINT copybits_flag;
SDLDropTarget *drop_target;
int dpi;
};

extern bool WIN_CreateWindow(SDL_VideoDevice *_this, SDL_Window *window, SDL_PropertiesID create_props);
Expand Down Expand Up @@ -144,6 +145,7 @@ extern bool WIN_AdjustWindowRect(SDL_Window *window, int *x, int *y, int *width,
extern bool WIN_AdjustWindowRectForHWND(HWND hwnd, LPRECT lpRect, UINT frame_dpi);
extern bool WIN_SetWindowParent(SDL_VideoDevice *_this, SDL_Window *window, SDL_Window *parent);
extern bool WIN_SetWindowModal(SDL_VideoDevice *_this, SDL_Window *window, bool modal);
extern int WIN_GetWindowDpi(SDL_VideoDevice *_this, SDL_Window *window);

// Ends C function definitions when using C++
#ifdef __cplusplus
Expand Down
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