Add wlr_output_impl.rollback

Most of the pending output state is not forwarded to the backend prior
to an output commit. For instance, wlr_output_set_mode just stashes the
mode without calling any wlr_output_impl function.
wlr_output_impl.commit is responsible for applying the pending mode.

However, there are exceptions to this rule. The first one is
wlr_output_attach_render. It won't go away before renderer v6 is
complete, because it needs to set the current EGL surface.

The second one is wlr_output_attach_buffer.
wlr_output_impl.attach_buffer is removed in [1].

When wlr_output_rollback is called, all pending state is supposed to be
cleared. This works for all the state except the two exceptions
mentionned above. To fix this, introduce wlr_output_impl.rollback.

Right now, the backend resets the current EGL surface. This prevents GL
commands from affecting the output after wlr_output_rollback.

This patch is required for FBO-based outputs to work properly. The
compositor might be using FBOs for its own purposes [2], having leftover
FBO state can have bad consequences.

[1]: https://github.com/swaywm/wlroots/pull/2097
[2]: https://github.com/swaywm/wlroots/pull/2063#issuecomment-597614312

4 files changed, 26 insertions, 0 deletions

diff --git a/backend/drm/drm.c b/backend/drm/drm.c
index 3bdb288e..55760015 100644
--- a/backend/drm/drm.c
+++ b/backend/drm/drm.c
@@ -574,6 +574,11 @@ static bool drm_connector_commit(struct wlr_output *output) {
 	return true;
 }
 
+static void drm_connector_rollback(struct wlr_output *output) {
+	struct wlr_drm_backend *drm = get_drm_backend_from_backend(output->backend);
+	wlr_egl_make_current(&drm->renderer.egl, EGL_NO_SURFACE, NULL);
+}
+
 static void fill_empty_gamma_table(size_t size,
 		uint16_t *r, uint16_t *g, uint16_t *b) {
 	assert(0xFFFF < UINT64_MAX / (size - 1));
@@ -1094,6 +1099,7 @@ static const struct wlr_output_impl output_impl = {
 	.attach_render = drm_connector_attach_render,
 	.test = drm_connector_test,
 	.commit = drm_connector_commit,
+	.rollback = drm_connector_rollback,
 	.set_gamma = set_drm_connector_gamma,
 	.get_gamma_size = drm_connector_get_gamma_size,
 	.export_dmabuf = drm_connector_export_dmabuf,
diff --git a/backend/headless/output.c b/backend/headless/output.c
index 18847af0..918581f5 100644
--- a/backend/headless/output.c
+++ b/backend/headless/output.c
@@ -97,6 +97,12 @@ static bool output_commit(struct wlr_output *wlr_output) {
 	return true;
 }
 
+static void output_rollback(struct wlr_output *wlr_output) {
+	struct wlr_headless_output *output =
+		headless_output_from_output(wlr_output);
+	wlr_egl_make_current(&output->backend->egl, EGL_NO_SURFACE, NULL);
+}
+
 static void output_destroy(struct wlr_output *wlr_output) {
 	struct wlr_headless_output *output =
 		headless_output_from_output(wlr_output);
@@ -113,6 +119,7 @@ static const struct wlr_output_impl output_impl = {
 	.destroy = output_destroy,
 	.attach_render = output_attach_render,
 	.commit = output_commit,
+	.rollback = output_rollback,
 };
 
 bool wlr_output_is_headless(struct wlr_output *wlr_output) {
diff --git a/backend/wayland/output.c b/backend/wayland/output.c
index ae58b584..07c5ec8d 100644
--- a/backend/wayland/output.c
+++ b/backend/wayland/output.c
@@ -302,6 +302,12 @@ static bool output_commit(struct wlr_output *wlr_output) {
 	return true;
 }
 
+static void output_rollback(struct wlr_output *wlr_output) {
+	struct wlr_wl_output *output =
+		get_wl_output_from_output(wlr_output);
+	wlr_egl_make_current(&output->backend->egl, EGL_NO_SURFACE, NULL);
+}
+
 static bool output_set_cursor(struct wlr_output *wlr_output,
 		struct wlr_texture *texture, int32_t scale,
 		enum wl_output_transform transform,
@@ -431,6 +437,7 @@ static const struct wlr_output_impl output_impl = {
 	.attach_render = output_attach_render,
 	.test = output_test,
 	.commit = output_commit,
+	.rollback = output_rollback,
 	.set_cursor = output_set_cursor,
 	.move_cursor = output_move_cursor,
 };
diff --git a/backend/x11/output.c b/backend/x11/output.c
index 4e016afe..f2b90cd3 100644
--- a/backend/x11/output.c
+++ b/backend/x11/output.c
@@ -162,11 +162,17 @@ static bool output_commit(struct wlr_output *wlr_output) {
 	return true;
 }
 
+static void output_rollback(struct wlr_output *wlr_output) {
+	struct wlr_x11_output *output = get_x11_output_from_output(wlr_output);
+	wlr_egl_make_current(&output->x11->egl, EGL_NO_SURFACE, NULL);
+}
+
 static const struct wlr_output_impl output_impl = {
 	.destroy = output_destroy,
 	.attach_render = output_attach_render,
 	.test = output_test,
 	.commit = output_commit,
+	.rollback = output_rollback,
 };
 
 struct wlr_output *wlr_x11_output_create(struct wlr_backend *backend) {