feat: advertise alpha-modifier-v1 (passive surface alpha)

README.md

@@ -502,6 +502,14 @@ compositor (sound, visual flash, or nothing); kick logs each ring as
 `[bell] ring` at `KICK_LOG=1` and otherwise renders nothing, keeping
 the quiet-by-default contract.
 
+## Alpha modifier (`alpha-modifier-v1`)
+
+Kick advertises `wp_alpha_modifier_v1`, so clients can multiply their
+surface's alpha (fades, translucent video) without repainting.
+wlroots applies the multiplier when rendering, so like color
+representation this is a passive correctness handshake rather than
+visible compositor work.
+
 ## Logging (`KICK_LOG`)
 
 Quiet by default: a plain launch prints nothing to the launching terminal

kick.c

@@ -75,6 +75,7 @@
 #include <wlr/render/swapchain.h>
 #include <wlr/render/wlr_renderer.h>
 #include <wlr/render/wlr_texture.h>
+#include <wlr/types/wlr_alpha_modifier_v1.h>
 #include <wlr/types/wlr_buffer.h>
 #include <wlr/types/wlr_color_management_v1.h>
 #include <wlr/types/wlr_color_representation_v1.h>
@@ -405,6 +406,10 @@ struct kick_server {
        internally, we only query the type for the debug log. */
     struct wlr_content_type_manager_v1 *content_type_mgr;
     struct wlr_single_pixel_buffer_manager_v1 *single_pixel_mgr;
+    /* Alpha modifier (wp_alpha_modifier_v1): a surface multiplies its own
+       alpha (fades, translucent video).  Fully passive: wlroots applies
+       the multiplier when rendering, so advertising is the whole job. */
+    struct wlr_alpha_modifier_v1 *alpha_modifier_mgr;
     /* Primary selection (zwp_primary_selection_v1).  Clients request the
        selection on their seat device; the request handler below is what
        actually installs it on the seat, mirroring the clipboard path. */
@@ -11875,6 +11880,9 @@ int main(int argc, char *argv[]) {
         wlr_content_type_manager_v1_create(server.wl_display, 1);
     server.single_pixel_mgr =
         wlr_single_pixel_buffer_manager_v1_create(server.wl_display);
+    /* Alpha modifier: one passive global (see the field comment). */
+    server.alpha_modifier_mgr =
+        wlr_alpha_modifier_v1_create(server.wl_display);
 
     /* Let nested clients pick their cursor shape (cursor-shape-v1); the
        manager is passive, so we handle request_set_shape ourselves below:

meson.build

@@ -311,6 +311,14 @@ protocols = {
         wl_protocols_dir / 'staging/single-pixel-buffer/single-pixel-buffer-v1.xml',
         'single-pixel-buffer-v1',
     ],
+    # Alpha modifier (a surface multiplies its own alpha): staging
+    # protocol from the system wayland-protocols.  Only client stubs are
+    # needed for wltest; the server side is wlroots'
+    # wlr_alpha_modifier_v1.
+    'alpha-modifier': [
+        wl_protocols_dir / 'staging/alpha-modifier/alpha-modifier-v1.xml',
+        'alpha-modifier-v1',
+    ],
     # Viewporter (stable): only the client stub is needed (the server side
     # is wlroots' wlr_viewporter_create).  wltest uses it to scale a 1x1
     # single-pixel buffer up to the window size.
@@ -436,6 +444,7 @@ executable('wltest',
            code_by_name['input-method'],
            code_by_name['content-type'],
            code_by_name['single-pixel'],
+           code_by_name['alpha-modifier'],
            code_by_name['viewporter'],
            code_by_name['gamma-control'],
            code_by_name['xdg-dialog'],
@@ -464,6 +473,7 @@ executable('wltest',
            client_headers['input-method'],
            client_headers['content-type'],
            client_headers['single-pixel'],
+           client_headers['alpha-modifier'],
            client_headers['viewporter'],
            client_headers['gamma-control'],
            client_headers['xdg-dialog'],

tests/test_smoke.py

@@ -1360,7 +1360,8 @@ def test_standalone_headless_protocol_globals(globals_session, tmp_path):
                  "wp_presentation", "zxdg_output_manager_v1",
                  "wp_viewporter", "wl_fixes",
                  "xdg_toplevel_tag_manager_v1",
-                 "wp_color_representation_manager_v1"):
+                 "wp_color_representation_manager_v1",
+                 "wp_alpha_modifier_v1"):
         assert want in names, \
             f"missing global {want}; advertised: {sorted(names)}"