Partial implementation of ext_image_copy_capture_v1 cursor sessions by jhenstridge · Pull Request #4632 · canonical/mir

jhenstridge · 2026-01-14T01:28:12Z

What's new?

This implements cursor the cursor session parts of the ext_image_copy_capture_v1 protocol. At present, it sends a dummy cursor image, which will be replaced with the real cursor in a follow-up PR.

Cursor position tracking is done via the CursorObserverMultiplexer, with a source-dependent backend class responsible for transforming the output space cursor coordinates to those of the corresponding image capture, and indicating whether the cursor is within bounds.

This can be tested like so:

Run miral with the following command:

./bin/miral-app --add-wayland-extensions ext_output_image_capture_source_manager_v1:ext_image_copy_capture_manager_v1:zwlr_virtual_pointer_manager_v1:zwp_virtual_keyboard_manager_v1

Run wayvnc with WAYLAND_DISPLAY=wayland-1 wayvnc
Connect using a VNC client that supports client side cursors. Remina works here, but GNOME Connections does not.
See that the placeholder white triangle cursor is displayed.

Checklist

Tests added and pass
Adequate documentation added
(optional) Added Screenshots or videos

Copilot

Pull request overview

This PR implements cursor session support for the ext_image_copy_capture_v1 Wayland protocol. The implementation adds cursor position tracking via CursorObserverMultiplexer and a backend architecture for transforming output-space coordinates to capture-space coordinates.

Changes:

Extended the image copy capture manager to accept cursor observer and clock dependencies
Implemented cursor session class with position tracking and visibility management
Added backend abstraction for coordinate mapping between different capture sources

Reviewed changes

Copilot reviewed 5 out of 5 changed files in this pull request and generated 3 comments.

Show a summary per file

File	Description
wayland_default_configuration.cpp	Passes cursor observer multiplexer and clock to image copy capture manager factory
wayland_connector.h	Adds cursor observer multiplexer and clock to WaylandExtensions context
wayland_connector.cpp	Wires cursor observer multiplexer through connector constructor
ext_image_capture_v1.h	Updates function signatures to accept new dependencies
ext_image_capture_v1.cpp	Implements cursor session tracking, coordinate mapping, and placeholder cursor rendering

Copilot · 2026-01-14T11:11:53Z

src/server/frontend_wayland/ext_image_capture_v1.cpp

+    auto data = mapping->data();
+    auto size = mapping->size();
+    auto stride = mapping->stride();
+    printf("Buffer length is %d (%dx%d, stride %d)\n", (int)mapping->len(), size.width.as_int(), size.height.as_int(), stride.as_int());


Debug print statements should be removed before merging. Use proper logging infrastructure if diagnostic output is needed.

src/server/frontend_wayland/ext_image_capture_v1.cpp

AlanGriffiths

There's some tidy-up that can be done now and not wait for a follow-up

src/server/frontend_wayland/ext_image_capture_v1.cpp

AlanGriffiths · 2026-01-14T11:44:39Z

src/server/frontend_wayland/ext_image_capture_v1.cpp

+    for (int y = 0; y < size.height.as_int(); y++)
+    {
+        for (int x = 0; x < size.width.as_int(); x++)
+        {
+            auto pos = y * stride.as_int() + x * 4;
+
+            if (x <= y)
+            {
+                data[pos] = std::byte{0xff};
+                data[pos+1] = std::byte{0xff};
+                data[pos+2] = std::byte{0xff};
+                data[pos+3] = std::byte{0xff};
+            }
+            else
+            {
+                data[pos] = std::byte{0x00};
+                data[pos+1] = std::byte{0x00};
+                data[pos+2] = std::byte{0x00};
+                data[pos+3] = std::byte{0x00};
+            }
+        }
+    }


I guess this temporary faking for image capture? I won't whine about the C-style loops

mattkae

Some structural thoughts, but looks mostly reasonable!

src/server/frontend_wayland/ext_image_capture_v1.cpp

AlanGriffiths · 2026-01-22T09:47:01Z

src/server/frontend_wayland/ext_image_capture_v1.cpp

+    // From CursorObserver
+    void cursor_moved_to(float abs_x, float abs_y);


What does this comment mean? ExtImageCopyCaptureCursorSessionV1 is not a CursorObserver

@jhenstridge why do you keep marking this comment "resolved"? It still seems valid to me

Still a confusing comment

AlanGriffiths

Can we correct the misleading comment on ExtImageCopyCaptureCursorSessionV1::cursor_moved_to()?

AlanGriffiths

Can we correct the misleading comment on the declaration of ExtImageCopyCaptureCursorSessionV1::cursor_moved_to()?

…tensions

The session uses the CursorObserverMultiplexer to track the cursor position, and a source-dependent backend class to transform the output space coordinates to match those of the captured image. Currently it sends a white triangle as the cursor image rather than the actual cursor image.

* Remove some debug statements * Clean up cursor position transformation

…tion While the class could potentially be extended to send a shutdown event to the cursor session's image copy session, clients will likely act on the shutdown signal on the main image copy session. That leaves us with a class providing a single virtual method, so passing a closure seems simpler.

…essionV1::CursorObserver The observer will not be invoked after it has been unregistered and freed by the cursor session, so we don't need to repeat this protection.

github-actions · 2026-01-29T10:31:28Z

TICS Quality Gate

✔️ Passed

mir

Coding Standards: ✔️ Passed

✔️ Condition “No new Coding Standard Violations for level 1, 2, 3 with respect to Previous analysis” passed.

See the results in the TICS Viewer

The following files have been checked for this project

src/server/frontend_wayland/ext_image_capture_v1.cpp
src/server/frontend_wayland/ext_image_capture_v1.h
src/server/frontend_wayland/wayland_connector.cpp
src/server/frontend_wayland/wayland_connector.h
src/server/frontend_wayland/wayland_default_configuration.cpp

TICS / TICS / Run TICS analysis

mattkae

Cool by me! I'll let Alan's feedback take it over the line

mattkae · 2026-02-02T14:58:44Z

src/server/frontend_wayland/ext_image_capture_v1.cpp

+    : public mi::CursorObserver
+{
+public:
+    CursorObserver(ExtImageCopyCaptureCursorSessionV1& session)


Nit:

Suggested change

CursorObserver(ExtImageCopyCaptureCursorSessionV1& session)

explicit CursorObserver(ExtImageCopyCaptureCursorSessionV1& session)

Yes, better to be consistent.

AlanGriffiths

Cool by me! I'll let Alan's feedback take it over the line

Just the same feedback I left two weeks ago

AlanGriffiths · 2026-02-02T16:42:03Z

src/server/frontend_wayland/ext_image_capture_v1.cpp

+    // From CursorObserver
+    void cursor_moved_to(float abs_x, float abs_y);


Still a confusing comment

AlanGriffiths · 2026-02-02T16:43:12Z

src/server/frontend_wayland/ext_image_capture_v1.cpp

+    : public mi::CursorObserver
+{
+public:
+    CursorObserver(ExtImageCopyCaptureCursorSessionV1& session)


Yes, better to be consistent.

jhenstridge requested a review from a team as a code owner January 14, 2026 01:28

AlanGriffiths requested a review from Copilot January 14, 2026 11:11

Copilot AI reviewed Jan 14, 2026

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AlanGriffiths requested changes Jan 14, 2026

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mattkae requested changes Jan 16, 2026

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src/server/frontend_wayland/ext_image_capture_v1.cpp Outdated Show resolved Hide resolved

src/server/frontend_wayland/ext_image_capture_v1.cpp Outdated Show resolved Hide resolved

src/server/frontend_wayland/ext_image_capture_v1.cpp Outdated Show resolved Hide resolved

jhenstridge force-pushed the wayland-ext-image-copy-capture-cursor branch from 4f6c309 to 0ee4284 Compare January 22, 2026 05:22

AlanGriffiths requested changes Jan 22, 2026

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AlanGriffiths requested changes Jan 23, 2026

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AlanGriffiths requested changes Jan 28, 2026

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jhenstridge added 6 commits January 29, 2026 17:38

wayland: expose the Clock and CursorObserverMultiplexer to Wayland ex…

29241e5

…tensions

wayland: fixes based on review comments

9cf2e32

* Remove some debug statements * Clean up cursor position transformation

wayland: remove the wayland::Weak usage in ExtImageCopyCaptureCursorS…

10cd019

…essionV1::CursorObserver The observer will not be invoked after it has been unregistered and freed by the cursor session, so we don't need to repeat this protection.

wayland: remove some outdated comments and a [[maybe_unused]] attribute

e34b6b7

jhenstridge force-pushed the wayland-ext-image-copy-capture-cursor branch from 837a8da to e34b6b7 Compare January 29, 2026 09:57

mattkae approved these changes Feb 2, 2026

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AlanGriffiths requested changes Feb 2, 2026

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		// From CursorObserver
		void cursor_moved_to(float abs_x, float abs_y);

	CursorObserver(ExtImageCopyCaptureCursorSessionV1& session)
	explicit CursorObserver(ExtImageCopyCaptureCursorSessionV1& session)

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jhenstridge commented Jan 14, 2026

What's new?

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github-actions bot commented Jan 29, 2026

TICS Quality Gate

✔️ Passed

mir

Coding Standards: ✔️ Passed

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3 participants