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wayland: Use manual masking on KDE for non-native aspect fullscreen modes

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KDE doesn't automatically center and mask fullscreen windows that don't match the display aspect ratio, so they are masked manually.

Can be removed when https://invent.kde.org/plasma/kwin/-/merge_requests/6953 is merged.
This commit is contained in:
Frank Praznik
2026-04-25 11:32:19 -04:00
parent 80a5905075
commit c65c809337
1 changed files with 37 additions and 16 deletions
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53
src/video/wayland/SDL_waylandwindow.c
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@@ -53,6 +53,41 @@
#include <libdecor.h>
#endif
/* According to the Wayland spec:
*
* "If the [fullscreen] surface doesn't cover the whole output, the compositor will
* position the surface in the center of the output and compensate with border fill
* covering the rest of the output. The content of the border fill is undefined, but
* should be assumed to be in some way that attempts to blend into the surrounding area
* (e.g. solid black)."
*
* KDE (6.7 at the time of writing) doesn't do this (https://invent.kde.org/plasma/kwin/-/merge_requests/6953),
* so fullscreen modes that don't cover the output need to be manually masked.
*
* This must not be done universally, as some compositors do not correctly honor subsurface
* offsets on fullscreen windows, but those also follow the spec regarding automatic masking
* around fullscreen windows, so SDL doesn't need to apply its own mask.
*
* TODO: Remove this once KDE is spec-compliant.
*/
static bool ShouldMaskFullscreen()
{
static int mask_required = -1;
if (mask_required >= 0) {
return mask_required != 0;
}
const char *desktop = SDL_getenv("XDG_CURRENT_DESKTOP");
if (desktop && SDL_strcmp(desktop, "KDE") == 0) {
mask_required = 1;
} else {
mask_required = 0;
}
return mask_required != 0;
}
static double GetWindowScale(SDL_Window *window)
{
return (window->flags & SDL_WINDOW_HIGH_PIXEL_DENSITY) || window->internal->scale_to_display ? window->internal->scale_factor : 1.0;
@@ -73,20 +108,6 @@ static int PixelToPoint(SDL_Window *window, int pixel)
return pixel ? SDL_max((int)SDL_lround((double)pixel / GetWindowScale(window)), 1) : 0;
}
/* According to the Wayland spec:
*
* "If the [fullscreen] surface doesn't cover the whole output, the compositor will
* position the surface in the center of the output and compensate with border fill
* covering the rest of the output. The content of the border fill is undefined, but
* should be assumed to be in some way that attempts to blend into the surrounding area
* (e.g. solid black)."
*
* - KDE, as of 5.27, still doesn't do this
* - GNOME prior to 43 didn't do this (older versions are still found in many LTS distros)
*
* Default to 'stretch' for now, until things have moved forward enough that the default
* can be changed to 'aspect'.
*/
enum WaylandModeScale
{
WAYLAND_MODE_SCALE_UNDEFINED,
@@ -479,9 +500,9 @@ static void ConfigureWindowGeometry(SDL_Window *window)
}
/* Calculate the mask size and offset.
* Fullscreen windows are centered and masked automatically by the compositor.
* Fullscreen windows are centered and masked automatically by the compositor, unless it lacks the capability.
*/
if (data->viewport && data->waylandData->subcompositor && !data->is_fullscreen &&
if (data->viewport && data->waylandData->subcompositor && (!data->is_fullscreen || ShouldMaskFullscreen()) &&
(viewport_width != data->current.logical_width || viewport_height != data->current.logical_height)) {
struct wl_buffer *old_buffer = NULL;