From 3bec9ff1bcb7fb8b93693c0c93b8d42797f95e1c Mon Sep 17 00:00:00 2001
From: Daniel Schadt <kingdread@gmx.de>
Date: Sat, 11 Mar 2023 20:02:17 +0100
Subject: add reference to small PNG crafting

---
 src/renderer/tilehunt.rs | 8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/src/renderer/tilehunt.rs b/src/renderer/tilehunt.rs
index f44644b..55b30af 100644
--- a/src/renderer/tilehunt.rs
+++ b/src/renderer/tilehunt.rs
@@ -1,4 +1,9 @@
 //! Actual rendering functions for tile hunts.
+//!
+//! This renders a tile as "transparent green" if any track passes through it.
+//!
+//! Note that is version of "tile hunt" is a bit silly, as the tile size changes with the zoom
+//! level. For a better version, the "tile hunt size" should be fixed to a given zoom.
 use color_eyre::eyre::Result;
 use crossbeam_channel::Sender;
 use fnv::FnvHashSet;
@@ -35,6 +40,9 @@ impl super::Renderer for Renderer {
     }
 
     fn colorize(layer: Self::Prepared, tx: Sender<RenderedTile>) -> Result<()> {
+        // The tile is hand-crafted to be very small. See
+        // <https://www.mjt.me.uk/posts/smallest-png/> for a reference, and of course the actual
+        // PNG specification <http://www.libpng.org/pub/png/spec/1.2/PNG-Contents.html>.
         static IMAGE_DATA: &[u8] = include_bytes!("tile-marked.png");
         for (tile_x, tile_y) in layer {
             tx.send(RenderedTile {
-- 
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