From 8ec64bb1b08fc33ebbaba41d391533d9ece56cef Mon Sep 17 00:00:00 2001
From: Daniel Barlow <dan@telent.net>
Date: Sun, 8 Jun 2025 17:59:46 +0100
Subject: [PATCH] rotate the map to face direction of travel

there is a bit of smoothing so it does not instantly lurch to the
new new course, as the visual effect was quite jarring
---
 pkgs/maps/main.fnl | 20 +++++++++++++++-----
 1 file changed, 15 insertions(+), 5 deletions(-)

diff --git a/pkgs/maps/main.fnl b/pkgs/maps/main.fnl
index d4089bb..ad4598c 100644
--- a/pkgs/maps/main.fnl
+++ b/pkgs/maps/main.fnl
@@ -65,7 +65,8 @@ label.readout {
             :lat 49
             :lon 0
             :zoom 17
-            :course 22
+            :course 0
+            :smooth-course 0
             }
  )
 
@@ -253,6 +254,10 @@ label.readout {
                   bounds.pixels.y)
                (draw-onto-map-surface bounds app-state.zoom)))))
 
+    (g:translate (+ (/ viewport-width 2))  (+ (/ viewport-height 2)))
+    (g:rotate (* (/ (- 360 app-state.smooth-course) 180) math.pi))
+    (g:translate (- (/ viewport-width 2))  (- (/ viewport-height 2)))
+
     (g:set_source_surface map-surface (- offset-x) (- offset-y))
     (g:set_operator cairo.Operator.SOURCE)
     (g:rectangle 0 0 viewport-width viewport-height)
@@ -293,9 +298,6 @@ label.readout {
 (expect= (hhmmss (+ 45 (* 60 12) (* 60 60 3))) "3:12:45")
 
 
-
-
-
 (fn update-app-state [new-vals]
   (let [old-bounds
         (map-bounds app-state.lat app-state.lon app-state.zoom)]
@@ -306,6 +308,9 @@ label.readout {
              (not (= old-bounds.min.x bounds.min.x))
              (not (= old-bounds.min.y bounds.min.y)))
         (set map-surface nil)))
+    (set app-state.smooth-course
+         (+ app-state.smooth-course
+            (* 0.05 (- app-state.course app-state.smooth-course))))
     (each [name widget (pairs state-widgets)]
       (case name
         :speed (widget:set_label
@@ -340,7 +345,8 @@ label.readout {
                  (fn [self g]
                    (g:set_source_rgb 0.4 0.0 0.1)
                    (g:translate (// height 2) (// height 2))
-                   (g:rotate (* (/ app-state.course 180) math.pi))
+                   (g:rotate (* (/ (- app-state.course app-state.smooth-course)
+                                   180) math.pi))
                    (g:translate (// height -2) (// height -2))
                    (g:set_line_width 4)
                    (g:move_to 10 height)
@@ -393,7 +399,11 @@ label.readout {
  GLib.PRIORITY_DEFAULT
  20 ; ms
  (fn []
+   ;; run cqueues scheduler
    (cq:step 0)
+   ;; for smoother rotation when course changes, repaint more often than
+   ;; once per gnss message
+   (update-app-state {})
    true)
  nil nil)