From 42db49c6fe6e7fb3d1ce62757abc3d8805cc55ff Mon Sep 17 00:00:00 2001
From: Simon Ser <contact@emersion.fr>
Date: Sun, 8 Sep 2019 18:33:09 +0300
Subject: [PATCH] Guess zpos from plane type

Many drivers don't expose the zpos plane property. We can guess it from the
plane type though: primary, overlay, cursor. Except some drivers expose
underlays too: underlays, primary, overlay, cursor. Underlay planes don't have a
special type, they are just marked as overlays. To detect them, check whether
their plane ID is less than the primary plane ID.

References: https://github.com/emersion/libhwc/issues/3
---
 display.c         | 38 +++++++++++++++++++++++++++++++++++++-
 include/private.h |  1 +
 2 files changed, 38 insertions(+), 1 deletion(-)

diff --git a/display.c b/display.c
index 7b31026..ddf844e 100644
--- a/display.c
+++ b/display.c
@@ -7,7 +7,33 @@
 #include <unistd.h>
 #include "private.h"
 
-static struct hwc_plane *plane_create(struct hwc_display *display, int32_t id)
+static int guess_plane_zpos_from_type(struct hwc_display *display,
+				      uint32_t plane_id, int type)
+{
+	struct hwc_plane *primary;
+
+	/* From far to close to the eye: primary, overlay, cursor. Unless
+	 * the overlay ID < primary ID. */
+	switch (type) {
+	case DRM_PLANE_TYPE_PRIMARY:
+		return 0;
+	case DRM_PLANE_TYPE_CURSOR:
+		return 2;
+	case DRM_PLANE_TYPE_OVERLAY:
+		if (hwc_list_empty(&display->planes)) {
+			return 0; /* No primary plane, shouldn't happen */
+		}
+		primary = hwc_container_of(display->planes.next, primary, link);
+		if (plane_id < primary->id) {
+			return -1;
+		} else {
+			return 1;
+		}
+	}
+	return 0;
+}
+
+static struct hwc_plane *plane_create(struct hwc_display *display, uint32_t id)
 {
 	struct hwc_plane *plane;
 	drmModePlane *drm_plane;
@@ -15,6 +41,7 @@ static struct hwc_plane *plane_create(struct hwc_display *display, int32_t id)
 	uint32_t i;
 	drmModePropertyRes *drm_prop;
 	struct hwc_plane_property *prop;
+	int type = -1;
 
 	plane = calloc(1, sizeof(*plane));
 	if (plane == NULL) {
@@ -52,9 +79,18 @@ static struct hwc_plane *plane_create(struct hwc_display *display, int32_t id)
 		prop->id = drm_prop->prop_id;
 		drmModeFreeProperty(drm_prop);
 		plane->props_len++;
+
+		if (strcmp(prop->name, "type") == 0) {
+			type = drm_props->prop_values[i];
+		}
 	}
 	drmModeFreeObjectProperties(drm_props);
 
+	if (type >= 0) {
+		plane->zpos = guess_plane_zpos_from_type(display, plane->id,
+							 type);
+	}
+
 	hwc_list_insert(display->planes.prev, &plane->link);
 
 	return plane;
diff --git a/include/private.h b/include/private.h
index 665b3dd..936180a 100644
--- a/include/private.h
+++ b/include/private.h
@@ -41,6 +41,7 @@ struct hwc_layer_property {
 struct hwc_plane {
 	uint32_t id;
 	uint32_t possible_crtcs;
+	int zpos; /* greater values mean closer to the eye */
 	/* TODO: formats */
 	struct hwc_list link; /* hwc_display.planes */