From 380c5e74102a0232e547decf9dfac2ebe79cf857 Mon Sep 17 00:00:00 2001
From: Daniel Barlow <dan@telent.net>
Date: Mon, 2 Jun 2025 13:35:10 +0100
Subject: [PATCH] rewrite map-bouds to get less off-screen tiles

---
 pkgs/maps/main.fnl | 52 +++++++++++++++++++++++++++++++++++-----------
 1 file changed, 40 insertions(+), 12 deletions(-)

diff --git a/pkgs/maps/main.fnl b/pkgs/maps/main.fnl
index f6e894a..5b5e367 100644
--- a/pkgs/maps/main.fnl
+++ b/pkgs/maps/main.fnl
@@ -75,20 +75,48 @@ label.readout {
 
 
 
-(fn map-bounds [lat lon zoom]
-  (let [num-tiles-x (+ 1 (math.ceil (/ map-width tile-size)))
-        num-tiles-y (+ 1 (math.ceil (/ map-height tile-size)))
-        (tile-x tile-y) (tiles.latlon->tile app-state.lat app-state.lon app-state.zoom)
-        min-tile-x (math.floor (- tile-x (/ num-tiles-x 2)))
-        max-tile-x (+ min-tile-x num-tiles-x 4)
-        min-tile-y (math.floor (- tile-y (/ num-tiles-y 2)))
-        max-tile-y (+ min-tile-y num-tiles-y 4)]
+(fn map-bounds-tile [tile-x tile-y]
+  (let [min-tile-x (math.floor (- tile-x (/ map-width tile-size 2)))
+        max-tile-x (math.floor (+ tile-x (/ map-width tile-size 2)))
+        min-tile-y (math.floor (- tile-y (/ map-height tile-size 2)))
+        max-tile-y (math.floor (+ tile-y (/ map-height tile-size 2)))]
     {
      :min { :x min-tile-x :y min-tile-y }
      :max { :x max-tile-x :y max-tile-y }
-     : num-tiles-x : num-tiles-y
+     :num-tiles-x (+ 1 (- max-tile-x min-tile-x))
+     :num-tiles-y (+ 1 (- max-tile-y min-tile-y))
      }))
 
+;; 720 width is 2.8 * 256 pixel tiles
+;; 800 height is 3.125 tiles
+
+(let [bounds (map-bounds-tile 65539.5 45014.5)]
+  ;; tile 65539, 45014 is centred on screen. left of it there is space
+  ;; for one tile and right of it likewise.
+  ;; vertical space for other tiles is (/ (- map-height tile-size) 256)
+  ;;  => 2.125 tiles, shared equally to top and bottom therefore
+  ;; 1.0625 tiles above and 1.0625 tiles below
+  
+  (expect= bounds.min {:x 65538 :y 45012})
+  (expect= bounds.max {:x 65540 :y 45016}))
+
+(let [bounds (map-bounds-tile 65539.0 45014.0)]
+  ;; top left corner of tile 65539, 45014 is centred on screen.
+  ;; to its left there are 360 pixels, so we need two tiles
+  ;; to its right there are 104 pixels, so one tile
+  ;; above there are 400 pixels: two tiles
+  ;; below are 144 pixels: one tile
+  
+  (expect= bounds.min {:x 65537 :y 45012})
+  (expect= bounds.max {:x 65540 :y 45015})
+  )
+
+(fn map-bounds [lat lon zoom]
+  (let [(tile-x tile-y) (tiles.latlon->tile app-state.lat app-state.lon app-state.zoom)]
+    (map-bounds-tile tile-x tile-y)))
+
+
+
 (local cq (cqueues.new))
 
 (var map-surface nil)
@@ -107,8 +135,8 @@ label.readout {
     (let [map-surface
           (window:create_similar_surface
            cairo.Content.COLOR
-           (* tile-size (+ 4 num-tiles-x))
-           (* tile-size (+ 4 num-tiles-y)))
+           (* tile-size (+ 1 num-tiles-x))
+           (* tile-size (+ 1 num-tiles-y)))
           g (cairo.Context.create map-surface)]
 
       (g:set_source_rgb 1 1 1)
@@ -137,7 +165,7 @@ label.readout {
       (set map-surface (cairo-the-map window))))
 
   (let [(tile-x tile-y) (tiles.latlon->tile app-state.lat app-state.lon app-state.zoom)
-        bounds (map-bounds tile-x tile-y)
+        bounds (map-bounds-tile tile-x tile-y)
         offset-x (- (* tile-size (- tile-x bounds.min.x)) (/ map-width 2))
         offset-y (- (* tile-size (- tile-y bounds.min.y)) (/ map-height 2))]