gtk4: Document paintable properties correctly

Part-of: <https://gitlab.freedesktop.org/gstreamer/gst-plugins-rs/-/merge_requests/1655>

docs/plugins/gst_plugins_cache.json

@@ -2565,7 +2565,7 @@
                         "controllable": false,
                         "mutable": "null",
                         "readable": true,
-                        "type": "GdkPaintable",
+                        "type": "GstGtk4Paintable",
                         "writable": false
                     }
                 },
@@ -2574,7 +2574,81 @@
         },
         "filename": "gstgtk4",
         "license": "MPL",
-        "other-types": {},
+        "other-types": {
+            "GstGtk4Paintable": {
+                "hierarchy": [
+                    "GstGtk4Paintable",
+                    "GObject"
+                ],
+                "interfaces": [
+                    "GdkPaintable"
+                ],
+                "kind": "object",
+                "properties": {
+                    "background-color": {
+                        "blurb": "Background color to render behind the video frame and in the borders",
+                        "conditionally-available": false,
+                        "construct": false,
+                        "construct-only": false,
+                        "controllable": false,
+                        "default": "255",
+                        "max": "-1",
+                        "min": "0",
+                        "mutable": "null",
+                        "readable": true,
+                        "type": "guint",
+                        "writable": true
+                    },
+                    "force-aspect-ratio": {
+                        "blurb": "When enabled, scaling will respect original aspect ratio",
+                        "conditionally-available": false,
+                        "construct": false,
+                        "construct-only": false,
+                        "controllable": false,
+                        "default": "false",
+                        "mutable": "null",
+                        "readable": true,
+                        "type": "gboolean",
+                        "writable": true
+                    },
+                    "gl-context": {
+                        "blurb": "GL context to use for rendering",
+                        "conditionally-available": false,
+                        "construct": false,
+                        "construct-only": true,
+                        "controllable": false,
+                        "mutable": "null",
+                        "readable": true,
+                        "type": "GdkGLContext",
+                        "writable": true
+                    },
+                    "scaling-filter": {
+                        "blurb": "Scaling filter to use for rendering",
+                        "conditionally-available": false,
+                        "construct": false,
+                        "construct-only": false,
+                        "controllable": false,
+                        "default": "linear (0)",
+                        "mutable": "null",
+                        "readable": true,
+                        "type": "GskScalingFilter",
+                        "writable": true
+                    },
+                    "use-scaling-filter": {
+                        "blurb": "Use selected scaling filter or GTK default for rendering",
+                        "conditionally-available": false,
+                        "construct": false,
+                        "construct-only": false,
+                        "controllable": false,
+                        "default": "false",
+                        "mutable": "null",
+                        "readable": true,
+                        "type": "gboolean",
+                        "writable": true
+                    }
+                }
+            }
+        },
         "package": "gst-plugin-gtk4",
         "source": "gst-plugin-gtk4",
         "tracers": {},

video/gtk4/src/lib.rs

@@ -19,9 +19,17 @@ use gst::glib;
 
 mod sink;
 mod utils;
+pub use sink::paintable::Paintable;
 pub use sink::PaintableSink;
 
 fn plugin_init(plugin: &gst::Plugin) -> Result<(), glib::BoolError> {
+    #[cfg(feature = "doc")]
+    {
+        use gst::prelude::*;
+
+        sink::paintable::Paintable::static_type().mark_as_plugin_api(gst::PluginAPIFlags::empty());
+    }
+
     #[cfg(not(feature = "gtk_v4_10"))]
     {
         if gtk::micro_version() >= 13 {

video/gtk4/src/sink/imp.rs

@@ -89,7 +89,7 @@ impl ObjectImpl for PaintableSink {
     fn properties() -> &'static [glib::ParamSpec] {
         static PROPERTIES: Lazy<Vec<glib::ParamSpec>> = Lazy::new(|| {
             vec![
-                glib::ParamSpecObject::builder::<gdk::Paintable>("paintable")
+                glib::ParamSpecObject::builder::<super::paintable::Paintable>("paintable")
                     .nick("Paintable")
                     .blurb("The Paintable the sink renders to")
                     .read_only()

video/gtk4/src/sink/mod.rs

@@ -40,7 +40,7 @@ use gtk::glib::prelude::*;
 
 mod frame;
 pub(super) mod imp;
-mod paintable;
+pub(super) mod paintable;
 
 enum SinkEvent {
     FrameChanged,

video/gtk4/src/sink/paintable/mod.rs

@@ -22,7 +22,7 @@ glib::wrapper! {
 }
 
 impl Paintable {
-    pub fn new(context: Option<gdk::GLContext>) -> Self {
+    pub(crate) fn new(context: Option<gdk::GLContext>) -> Self {
         glib::Object::builder()
             .property("gl-context", context)
             .build()