From 53e377cabdc3856c9b5fbf851b4b0e64bc8b5dde Mon Sep 17 00:00:00 2001
From: Daniel Barlow <dan@telent.net>
Date: Sun, 8 Jun 2025 19:10:11 +0100
Subject: [PATCH] widen map obunds so that rotation works

...without showing missing white bits in the corners when moving
diagonally
---
 pkgs/maps/main.fnl | 55 +++++++++++++++++++++++++---------------------
 1 file changed, 30 insertions(+), 25 deletions(-)

diff --git a/pkgs/maps/main.fnl b/pkgs/maps/main.fnl
index 32b0a5a..c1c8f66 100644
--- a/pkgs/maps/main.fnl
+++ b/pkgs/maps/main.fnl
@@ -77,13 +77,32 @@ label.readout {
 
 
 (fn map-bounds-tile [tile-x tile-y]
-  (let [min-tile-x (math.floor (- tile-x (/ viewport-width tile-size 2)))
-        max-tile-x (math.floor (+ tile-x (/ viewport-width tile-size 2)))
-        min-tile-y (math.floor (- tile-y (/ viewport-height tile-size 2)))
-        max-tile-y (math.floor (+ tile-y (/ viewport-height tile-size 2)))
+  ;; we fetch enough tiles around the current location that the screen
+  ;; can be freely rotated without needing to fetch more.
+
+  ;; when facing north, we have e.g.
+  ;; 720 width is 2.8 * 256 pixel tiles
+  ;; 800 height is 3.125 tiles
+  ;;
+  ;; however:
+  ;; - when the map is rotated 90 degrees we instead have
+  ;;   3.125 tiles horizontally and 2.8 vertically
+  ;; - at e.g a 45 degree angle ... something else?
+  ;;
+  ;; the furthest points visible from the centre of the screen are the
+  ;; corners.  So, we draw a circle about the centre which goes
+  ;; through those points.  To ensure we have enough tiles to fill the
+  ;; screen at any angle, we fetch every tile that's (partly
+  ;; or entirely) inside that circle
+
+  (let [radius (/ (math.sqrt (+ (^ viewport-width 2) (^ viewport-height 2)))
+                  tile-size 2)
+        min-tile-x (math.floor (- tile-x radius))
+        max-tile-x (math.floor (+ tile-x radius))
+        min-tile-y (math.floor (- tile-y radius))
+        max-tile-y (math.floor (+ tile-y radius))
         num-tiles-x (+ 1 (- max-tile-x min-tile-x))
         num-tiles-y (+ 1 (- max-tile-y min-tile-y))]
-
     {
      :min { :x min-tile-x :y min-tile-y }
      :max { :x max-tile-x :y max-tile-y }
@@ -95,28 +114,15 @@ label.readout {
               }
      }))
 
-;; 720 width is 2.8 * 256 pixel tiles
-;; 800 height is 3.125 tiles
+;; diagonal radius is 538 pixels, 2.1 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 (/ (- viewport-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}))
+  (expect= bounds.min {:x 65537 :y 45012})
+  (expect= bounds.max {:x 65541 :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})
+  (expect= bounds.min {:x 65536 :y 45011})
+  (expect= bounds.max {:x 65541 :y 45016})
   )
 
 (fn map-bounds [lat lon zoom]
@@ -260,8 +266,7 @@ label.readout {
 
     (g:set_source_surface map-surface (- offset-x) (- offset-y))
     (g:set_operator cairo.Operator.SOURCE)
-    (g:rectangle 0 0 viewport-width viewport-height)
-    (g:fill)))
+    (g:paint)))