gl/gir: Configure generation for GLFilter with miniobject quirks

GLMemory input/output objects cannot be passed as mutable:
to_glib_none_mut checks if the miniobject is writable, even though the
underlying implementation should really only care about whether the
_data_ owned by this miniobject is.

(This temporary GLMemory object references its parent buffer object
 that is also referenced externally, resulting in two references making
 the object itself immutable)

Furthermore take care of automatically calling `add_rgba_pad_templates`
in `class_init` if `ADD_RGBA_PAD_TEMPLATES` is set to `true` (the
default).

gstreamer-gl/Gir.toml

@@ -507,3 +507,29 @@ status = "generate"
     name = "attach"
     # attachment_point parameter unchecked
     unsafe = true
+
+[[object]]
+name = "GstGL.GLFilter"
+status = "generate"
+
+    [[object.function]]
+    name = "add_rgba_pad_templates"
+    # Automatically called if
+    # GLFilterImpl::ADD_RGBA_PAD_TEMPLATES is true
+    ignore = true
+
+    [[object.function]]
+    pattern = "render_to_target\\w*"
+        [[object.function.parameter]]
+        pattern = "input|output"
+        const = true
+
+    [[object.function]]
+    name = "render_to_target"
+        [object.function.return]
+        bool_return_is_error = "`func` returned `false`"
+
+    [[object.function]]
+    name = "filter_texture"
+        [object.function.return]
+        bool_return_is_error = "Failed to transform texture"

gstreamer-gl/src/lib.rs

@@ -58,3 +58,5 @@ pub mod prelude {
     pub use crate::gl_context::GLContextExtManual;
     pub use crate::gl_video_frame::VideoFrameGLExt;
 }
+
+pub mod subclass;

gstreamer-gl/src/subclass/gl_filter.rs

@@ -21,6 +21,10 @@ pub enum GLFilterMode {
 
 pub trait GLFilterImpl: GLFilterImplExt + GLBaseFilterImpl {
     const MODE: GLFilterMode;
+    // rustdoc-stripper-ignore-next
+    /// Calls [`add_rgba_pad_templates`](ffi::gst_gl_filter_add_rgba_pad_templates)
+    /// in [`GLFilter::class_init`] if [`true`].
+    const ADD_RGBA_PAD_TEMPLATES: bool = true;
 
     fn set_caps(
         &self,
@@ -239,6 +243,10 @@ unsafe impl<T: GLFilterImpl> IsSubclassable<T> for GLFilter {
                 klass.filter_texture = Some(filter_texture::<T>);
             }
         }
+
+        if <T as GLFilterImpl>::ADD_RGBA_PAD_TEMPLATES {
+            unsafe { ffi::gst_gl_filter_add_rgba_pad_templates(klass) }
+        }
     }
 
     fn instance_init(instance: &mut glib::subclass::InitializingObject<T>) {