output: add wlr_output_preferred_read_format()

The read format is dependent on the output, so we first need to make it
current. This fixes a race condition in wlr-screencopy-v1 where a dmabuf
client would cause EGL_NO_SURFACE to be bound at the time when
screencopy needs to query for the preferred format, causing GL errors.

2 files changed, 6 insertions, 5 deletions

diff --git a/include/wlr/render/wlr_renderer.h b/include/wlr/render/wlr_renderer.h
index 02b4a11e..9c031b7f 100644
--- a/include/wlr/render/wlr_renderer.h
+++ b/include/wlr/render/wlr_renderer.h
@@ -97,11 +97,6 @@ int wlr_renderer_get_dmabuf_formats(struct wlr_renderer *renderer,
 int wlr_renderer_get_dmabuf_modifiers(struct wlr_renderer *renderer, int format,
 	uint64_t **modifiers);
 /**
- * Get the preferred format for reading pixels.
- */
-bool wlr_renderer_preferred_read_format(struct wlr_renderer *renderer,
-	enum wl_shm_format *fmt);
-/**
  * Reads out of pixels of the currently bound surface into data. `stride` is in
  * bytes.
  *
diff --git a/include/wlr/types/wlr_output.h b/include/wlr/types/wlr_output.h
index 557a3895..6d38152a 100644
--- a/include/wlr/types/wlr_output.h
+++ b/include/wlr/types/wlr_output.h
@@ -193,6 +193,12 @@ void wlr_output_effective_resolution(struct wlr_output *output,
  */
 bool wlr_output_make_current(struct wlr_output *output, int *buffer_age);
 /**
+ * Get the preferred format for reading pixels.
+ * This function might change the current rendering context.
+ */
+bool wlr_output_preferred_read_format(struct wlr_output *output,
+	enum wl_shm_format *fmt);
+/**
  * Swaps the output buffers. If the time of the frame isn't known, set `when` to
  * NULL. If the compositor doesn't support damage tracking, set `damage` to
  * NULL.