wayland: Implement SetWindowOpacity via the alpha modifier protocol

The wp_alpha_modifier_v1 protocol allows for a global blending factor to be specified for an entire surface. Use this to add support for SDL_SetWindowOpacity().

src/video/wayland/SDL_waylandvideo.c

@@ -43,6 +43,7 @@
 
 #include <wayland-util.h>
 
+#include "alpha-modifier-v1-client-protocol.h"
 #include "cursor-shape-v1-client-protocol.h"
 #include "fractional-scale-v1-client-protocol.h"
 #include "idle-inhibit-unstable-v1-client-protocol.h"
@@ -487,6 +488,7 @@ static SDL_VideoDevice *Wayland_CreateDevice(void)
     device->SetWindowMinimumSize = Wayland_SetWindowMinimumSize;
     device->SetWindowMaximumSize = Wayland_SetWindowMaximumSize;
     device->SetWindowModalFor = Wayland_SetWindowModalFor;
+    device->SetWindowOpacity = Wayland_SetWindowOpacity;
     device->SetWindowTitle = Wayland_SetWindowTitle;
     device->GetWindowSizeInPixels = Wayland_GetWindowSizeInPixels;
     device->GetDisplayForWindow = Wayland_GetDisplayForWindow;
@@ -1107,6 +1109,8 @@ static void display_handle_global(void *data, struct wl_registry *registry, uint
         d->zxdg_exporter_v2 = wl_registry_bind(d->registry, id, &zxdg_exporter_v2_interface, 1);
     } else if (SDL_strcmp(interface, "xdg_wm_dialog_v1") == 0) {
         d->xdg_wm_dialog_v1 = wl_registry_bind(d->registry, id, &xdg_wm_dialog_v1_interface, 1);
+    } else if (SDL_strcmp(interface, "wp_alpha_modifier_v1") == 0) {
+        d->wp_alpha_modifier_v1 = wl_registry_bind(d->registry, id, &wp_alpha_modifier_v1_interface, 1);
     } else if (SDL_strcmp(interface, "kde_output_order_v1") == 0) {
         d->kde_output_order = wl_registry_bind(d->registry, id, &kde_output_order_v1_interface, 1);
         kde_output_order_v1_add_listener(d->kde_output_order, &kde_output_order_listener, d);
@@ -1369,6 +1373,11 @@ static void Wayland_VideoCleanup(SDL_VideoDevice *_this)
         data->xdg_wm_dialog_v1 = NULL;
     }
 
+    if (data->wp_alpha_modifier_v1) {
+        wp_alpha_modifier_v1_destroy(data->wp_alpha_modifier_v1);
+        data->wp_alpha_modifier_v1 = NULL;
+    }
+
     if (data->kde_output_order) {
         Wayland_FlushOutputOrder(data);
         kde_output_order_v1_destroy(data->kde_output_order);

src/video/wayland/SDL_waylandvideo.h

@@ -81,6 +81,7 @@ struct SDL_VideoData
     struct zwp_input_timestamps_manager_v1 *input_timestamps_manager;
     struct zxdg_exporter_v2 *zxdg_exporter_v2;
     struct xdg_wm_dialog_v1 *xdg_wm_dialog_v1;
+    struct wp_alpha_modifier_v1 *wp_alpha_modifier_v1;
     struct kde_output_order_v1 *kde_output_order;
 
     struct xkb_context *xkb_context;

src/video/wayland/SDL_waylandwindow.c

@@ -32,6 +32,7 @@
 #include "SDL_waylandvideo.h"
 #include "../../SDL_hints_c.h"
 
+#include "alpha-modifier-v1-client-protocol.h"
 #include "xdg-shell-client-protocol.h"
 #include "xdg-decoration-unstable-v1-client-protocol.h"
 #include "idle-inhibit-unstable-v1-client-protocol.h"
@@ -279,10 +280,24 @@ static void RepositionPopup(SDL_Window *window, SDL_bool use_current_position)
     }
 }
 
+static void SetSurfaceOpaqueRegion(SDL_WindowData *wind, SDL_bool is_opaque)
+{
+    SDL_VideoData *viddata = wind->waylandData;
+
+    if (is_opaque) {
+        struct wl_region *region = wl_compositor_create_region(viddata->compositor);
+        wl_region_add(region, 0, 0,
+                      wind->current.logical_width, wind->current.logical_height);
+        wl_surface_set_opaque_region(wind->surface, region);
+        wl_region_destroy(region);
+    } else {
+        wl_surface_set_opaque_region(wind->surface, NULL);
+    }
+}
+
 static void ConfigureWindowGeometry(SDL_Window *window)
 {
     SDL_WindowData *data = window->driverdata;
-    SDL_VideoData *viddata = data->waylandData;
     const int old_pixel_width = data->current.pixel_width;
     const int old_pixel_height = data->current.pixel_height;
     int window_width, window_height;
@@ -391,20 +406,12 @@ static void ConfigureWindowGeometry(SDL_Window *window)
      * need to be recalculated if the output size has changed.
      */
     if (window_size_changed) {
-        struct wl_region *region;
-
         /* libdecor does this internally on frame commits, so it's only needed for xdg surfaces. */
         if (data->shell_surface_type != WAYLAND_SURFACE_LIBDECOR && data->shell_surface.xdg.surface) {
             xdg_surface_set_window_geometry(data->shell_surface.xdg.surface, 0, 0, data->current.logical_width, data->current.logical_height);
         }
 
-        if (!(window->flags & SDL_WINDOW_TRANSPARENT)) {
-            region = wl_compositor_create_region(viddata->compositor);
-            wl_region_add(region, 0, 0,
-                          data->current.logical_width, data->current.logical_height);
-            wl_surface_set_opaque_region(data->surface, region);
-            wl_region_destroy(region);
-        }
+        SetSurfaceOpaqueRegion(data, !(window->flags & SDL_WINDOW_TRANSPARENT) && window->opacity == 1.0f);
 
         /* Ensure that child popup windows are still in bounds. */
         for (SDL_Window *child = window->first_child; child; child = child->next_sibling) {
@@ -2302,6 +2309,11 @@ int Wayland_CreateWindow(SDL_VideoDevice *_this, SDL_Window *window, SDL_Propert
         }
     }
 
+    if (!custom_surface_role && c->wp_alpha_modifier_v1) {
+        data->wp_alpha_modifier_surface_v1 = wp_alpha_modifier_v1_get_surface(c->wp_alpha_modifier_v1, data->surface);
+        wp_alpha_modifier_surface_v1_set_multiplier(data->wp_alpha_modifier_surface_v1, SDL_MAX_UINT32);
+    }
+
     /* Must be called before EGL configuration to set the drawable backbuffer size. */
     ConfigureWindowGeometry(window);
 
@@ -2494,6 +2506,20 @@ SDL_DisplayID Wayland_GetDisplayForWindow(SDL_VideoDevice *_this, SDL_Window *wi
     return 0;
 }
 
+int Wayland_SetWindowOpacity(SDL_VideoDevice *_this, SDL_Window *window, float opacity)
+{
+    SDL_WindowData *wind = window->driverdata;
+
+    if (wind->wp_alpha_modifier_surface_v1) {
+        SetSurfaceOpaqueRegion(wind, !(window->flags & SDL_WINDOW_TRANSPARENT) && opacity == 1.0f);
+        wp_alpha_modifier_surface_v1_set_multiplier(wind->wp_alpha_modifier_surface_v1, (Uint32)((double)SDL_MAX_UINT32 * (double)opacity));
+
+        return 0;
+    }
+
+    return SDL_SetError("wayland: set window opacity failed; compositor lacks support for the required wp_alpha_modifier_v1 protocol");
+}
+
 void Wayland_SetWindowTitle(SDL_VideoDevice *_this, SDL_Window *window)
 {
     SDL_WindowData *wind = window->driverdata;
@@ -2614,6 +2640,10 @@ void Wayland_DestroyWindow(SDL_VideoDevice *_this, SDL_Window *window)
             wp_fractional_scale_v1_destroy(wind->fractional_scale);
         }
 
+        if (wind->wp_alpha_modifier_surface_v1) {
+            wp_alpha_modifier_surface_v1_destroy(wind->wp_alpha_modifier_surface_v1);
+        }
+
         SDL_free(wind->outputs);
         SDL_free(wind->app_id);
 

src/video/wayland/SDL_waylandwindow.h

@@ -97,6 +97,7 @@ struct SDL_WindowData
     struct wp_fractional_scale_v1 *fractional_scale;
     struct zxdg_exported_v2 *exported;
     struct xdg_dialog_v1 *xdg_dialog_v1;
+    struct wp_alpha_modifier_surface_v1 *wp_alpha_modifier_surface_v1;
 
     SDL_AtomicInt swap_interval_ready;
 
@@ -193,6 +194,7 @@ extern void Wayland_SetWindowMaximumSize(SDL_VideoDevice *_this, SDL_Window *win
 extern void Wayland_GetWindowSizeInPixels(SDL_VideoDevice *_this, SDL_Window *window, int *w, int *h);
 extern SDL_DisplayID Wayland_GetDisplayForWindow(SDL_VideoDevice *_this, SDL_Window *window);
 extern int Wayland_SetWindowModalFor(SDL_VideoDevice *_this, SDL_Window *modal_window, SDL_Window *parent_window);
+extern int Wayland_SetWindowOpacity(SDL_VideoDevice *_this, SDL_Window *window, float opacity);
 extern void Wayland_SetWindowTitle(SDL_VideoDevice *_this, SDL_Window *window);
 extern void Wayland_ShowWindowSystemMenu(SDL_Window *window, int x, int y);
 extern void Wayland_DestroyWindow(SDL_VideoDevice *_this, SDL_Window *window);