kmsdrm: Report the panel orientation hint property

Queries the "panel orientation" property on the connector and reports it in degrees of clockwise rotation via the 'SDL.display.KMSDRM.panel_orientation' display property.

This is provided by the kernel as a hint to userspace applications, and the application itself is ultimately responsible for any required coordinate transformations needed to conform to the requested orientation.

include/SDL3/SDL_video.h

@@ -409,6 +409,13 @@ extern DECLSPEC SDL_DisplayID SDLCALL SDL_GetPrimaryDisplay(void);
  *   enabled, this will be 1.0. This property can change dynamically when
  *   SDL_EVENT_DISPLAY_HDR_STATE_CHANGED is sent.
  *
+ * On KMS/DRM:
+ *
+ * - `SDL_PROP_DISPLAY_KMSDRM_ORIENTATION_NUMBER`: the "panel orientation" property
+ *   for the display in degrees of clockwise rotation. Note that this is provided
+ *   only as a hint, and the application is responsible for any coordinate transformations
+ *   needed to conform to the requested display orientation.
+ *
  * \param displayID the instance ID of the display to query
  * \returns a valid property ID on success or 0 on failure; call
  *          SDL_GetError() for more information.
@@ -420,9 +427,10 @@ extern DECLSPEC SDL_DisplayID SDLCALL SDL_GetPrimaryDisplay(void);
  */
 extern DECLSPEC SDL_PropertiesID SDLCALL SDL_GetDisplayProperties(SDL_DisplayID displayID);
 
-#define SDL_PROP_DISPLAY_HDR_ENABLED_BOOLEAN            "SDL.display.HDR_enabled"
-#define SDL_PROP_DISPLAY_SDR_WHITE_POINT_FLOAT          "SDL.display.SDR_white_point"
-#define SDL_PROP_DISPLAY_HDR_HEADROOM_FLOAT             "SDL.display.HDR_headroom"
+#define SDL_PROP_DISPLAY_HDR_ENABLED_BOOLEAN             "SDL.display.HDR_enabled"
+#define SDL_PROP_DISPLAY_SDR_WHITE_POINT_FLOAT           "SDL.display.SDR_white_point"
+#define SDL_PROP_DISPLAY_HDR_HEADROOM_FLOAT              "SDL.display.HDR_headroom"
+#define SDL_PROP_DISPLAY_KMSDRM_PANEL_ORIENTATION_NUMBER "SDL.display.KMSDRM.panel_orientation"
 
 /**
  * Get the name of a display in UTF-8 encoding.

src/video/kmsdrm/SDL_kmsdrmvideo.c

@@ -673,6 +673,77 @@ static SDL_bool KMSDRM_CrtcGetVrr(uint32_t drm_fd, uint32_t crtc_id)
     return SDL_FALSE;
 }
 
+static SDL_bool KMSDRM_OrientationPropId(uint32_t drm_fd, uint32_t crtc_id, uint32_t *orientation_prop_id)
+{
+    drmModeObjectPropertiesPtr drm_props;
+
+    drm_props = KMSDRM_drmModeObjectGetProperties(drm_fd,
+                                                  crtc_id,
+                                                  DRM_MODE_OBJECT_CONNECTOR);
+
+    if (!drm_props) {
+        return SDL_FALSE;
+    }
+
+    *orientation_prop_id = KMSDRM_CrtcGetPropId(drm_fd,
+                                                drm_props,
+                                                "panel orientation");
+
+    KMSDRM_drmModeFreeObjectProperties(drm_props);
+
+    return SDL_TRUE;
+}
+
+static int KMSDRM_CrtcGetOrientation(uint32_t drm_fd, uint32_t crtc_id)
+{
+    uint32_t orientation_prop_id;
+    drmModeObjectPropertiesPtr props;
+    int i;
+    SDL_bool done = SDL_FALSE;
+    int orientation = 0;
+
+    if (!KMSDRM_OrientationPropId(drm_fd, crtc_id, &orientation_prop_id)) {
+        return orientation;
+    }
+
+    props = KMSDRM_drmModeObjectGetProperties(drm_fd,
+                                              crtc_id,
+                                              DRM_MODE_OBJECT_CONNECTOR);
+
+    if (!props) {
+        return orientation;
+    }
+
+    for (i = 0; i < props->count_props && !done; ++i) {
+        drmModePropertyPtr drm_prop = KMSDRM_drmModeGetProperty(drm_fd, props->props[i]);
+
+        if (!drm_prop) {
+            continue;
+        }
+
+        if (drm_prop->prop_id == orientation_prop_id && (drm_prop->flags & DRM_MODE_PROP_ENUM)) {
+            if (drm_prop->count_enums) {
+                /* "Normal" is the default of no rotation (0 degrees) */
+                if (SDL_strcmp(drm_prop->enums[0].name, "Left Side Up") == 0) {
+                    orientation = 90;
+                } else if (SDL_strcmp(drm_prop->enums[0].name, "Upside Down") == 0) {
+                    orientation = 180;
+                } else if (SDL_strcmp(drm_prop->enums[0].name, "Right Side Up") == 0) {
+                    orientation = 270;
+                }
+            }
+
+            done = SDL_TRUE;
+        }
+
+        KMSDRM_drmModeFreeProperty(drm_prop);
+    }
+
+    KMSDRM_drmModeFreeObjectProperties(props);
+
+    return orientation;
+}
+
 /* Gets a DRM connector, builds an SDL_Display with it, and adds it to the
    list of SDL Displays in _this->displays[]  */
 static void KMSDRM_AddDisplay(SDL_VideoDevice *_this, drmModeConnector *connector, drmModeRes *resources)
@@ -683,6 +754,9 @@ static void KMSDRM_AddDisplay(SDL_VideoDevice *_this, drmModeConnector *connecto
     SDL_DisplayModeData *modedata = NULL;
     drmModeEncoder *encoder = NULL;
     drmModeCrtc *crtc = NULL;
+    SDL_DisplayID display_id;
+    SDL_PropertiesID display_properties;
+    int orientation;
     int mode_index;
     int i, j;
     int ret = 0;
@@ -867,11 +941,16 @@ static void KMSDRM_AddDisplay(SDL_VideoDevice *_this, drmModeConnector *connecto
     display.desktop_mode.driverdata = modedata;
 
     /* Add the display to the list of SDL displays. */
-    if (SDL_AddVideoDisplay(&display, SDL_FALSE) == 0) {
+    display_id = SDL_AddVideoDisplay(&display, SDL_FALSE);
+    if (!display_id) {
         ret = -1;
         goto cleanup;
     }
 
+    orientation = KMSDRM_CrtcGetOrientation(viddata->drm_fd, crtc->crtc_id);
+    display_properties = SDL_GetDisplayProperties(display_id);
+    SDL_SetNumberProperty(display_properties, SDL_PROP_DISPLAY_KMSDRM_PANEL_ORIENTATION_NUMBER, orientation);
+
 cleanup:
     if (encoder) {
         KMSDRM_drmModeFreeEncoder(encoder);