Improve doc comments

Improve formatting and expand descriptions.

include/libliftoff.h

@@ -12,13 +12,21 @@ struct liftoff_output;
 struct liftoff_layer;
 
 /**
- * Initialize libliftoff for a DRM node. The node is expected to have
- * DRM_CLIENT_CAP_UNIVERSAL_PLANES and DRM_CLIENT_CAP_ATOMIC enabled.
+ * Initialize libliftoff for a DRM node.
+ *
+ * The node is expected to have DRM_CLIENT_CAP_UNIVERSAL_PLANES and
+ * DRM_CLIENT_CAP_ATOMIC enabled.
  */
 struct liftoff_device *liftoff_device_create(int drm_fd);
+/**
+ * Destroy a libliftoff device.
+ *
+ * The caller is expected to destroy the outputs and layers explicitly.
+ */
 void liftoff_device_destroy(struct liftoff_device *device);
 /**
  * Build a layer to plane mapping and append the plane configuration to `req`.
+ *
  * Callers are expected to commit `req` afterwards and can read the layer to
  * plane mapping with `liftoff_layer_get_plane_id`.
  *
@@ -28,46 +36,65 @@ bool liftoff_output_apply(struct liftoff_output *output, drmModeAtomicReq *req,
 			  uint32_t flags);
 
 /**
- * Make the device manage a CRTC's planes. The returned output allows callers
- * to attach layers.
+ * Make the device manage a CRTC's planes.
+ *
+ * The returned output allows callers to attach layers.
  */
 struct liftoff_output *liftoff_output_create(struct liftoff_device *device,
 					     uint32_t crtc_id);
+/**
+ * Destroy a libliftoff output.
+ *
+ * The caller is expected to destroy the output's layers explicitly.
+ */
 void liftoff_output_destroy(struct liftoff_output *output);
 /**
- * Indicate on which layer composition can take place. Users should be able to
- * blend layers that haven't been mapped to a plane to this layer. The
- * composition layer won't be used if all other layers have been mapped to a
- * plane. There is at most one composition layer per output.
+ * Indicate on which layer composition can take place.
+ *
+ * Users should be able to blend layers that haven't been mapped to a plane to
+ * this layer. The composition layer won't be used if all other layers have been
+ * mapped to a plane. There is at most one composition layer per output.
  */
 void liftoff_output_set_composition_layer(struct liftoff_output *output,
 					  struct liftoff_layer *layer);
 
 /**
  * Create a new layer on an output.
+ *
+ * A layer is a virtual plane. Users can create as many layers as they want and
+ * set any KMS property on them, without any constraint. libliftoff will try
+ * to map layers to hardware planes on a best-effort basis. The user will need
+ * to manually handle layers that couldn't be mapped to a plane.
  */
 struct liftoff_layer *liftoff_layer_create(struct liftoff_output *output);
+/**
+ * Destroy a layer.
+ */
 void liftoff_layer_destroy(struct liftoff_layer *layer);
 /**
- * Set a property on the layer. Any plane property can be set (except CRTC_ID).
- * If none of the planes support the property, the layer won't be mapped to any
- * plane.
+ * Set a property on the layer.
+ *
+ * Any plane property can be set (except CRTC_ID). If none of the planes support
+ * the property, the layer won't be mapped to any plane.
  *
  * Setting a zero FB_ID disables the layer.
  */
 void liftoff_layer_set_property(struct liftoff_layer *layer, const char *name,
 				uint64_t value);
 /**
- * Force composition on this layer. This unsets any previous FB_ID value. To
- * switch back to direct scan-out, set FB_ID again.
+ * Force composition on this layer.
+ *
+ * This unsets any previous FB_ID value. To switch back to direct scan-out, set
+ * FB_ID again.
  *
  * This can be used when no KMS FB ID is available for this layer but it still
  * needs to be displayed (e.g. the buffer cannot be imported in KMS).
  */
 void liftoff_layer_set_fb_composited(struct liftoff_layer *layer);
 /**
- * Retrieve the plane mapped to this layer. Zero is returned if no plane is
- * mapped.
+ * Retrieve the plane mapped to this layer.
+ *
+ * Zero is returned if no plane is mapped.
  */
 uint32_t liftoff_layer_get_plane_id(struct liftoff_layer *layer);
 
@@ -80,6 +107,13 @@ enum liftoff_log_importance {
 typedef void (*liftoff_log_func)(enum liftoff_log_importance importance,
 				 const char *fmt, va_list args);
 
+/**
+ * Initialize libliftoff's log infrastructure.
+ *
+ * Only messages with a priority higher than the provided `verbosity` will be
+ * logged. If `callback` is non-NULL, libliftoff will call the function instead
+ * of printing the messages to stderr.
+ */
 void liftoff_log_init(enum liftoff_log_importance verbosity,
 		      liftoff_log_func callback);