apply cubic scaling to heat count

1 files changed, 7 insertions, 0 deletions

diff --git a/hittekaart/src/renderer/heatmap.rs b/hittekaart/src/renderer/heatmap.rs
index 6400e82..d2c2452 100644
--- a/hittekaart/src/renderer/heatmap.rs
+++ b/hittekaart/src/renderer/heatmap.rs
@@ -140,6 +140,13 @@ fn prepare_lut(max: u8) -> Vec<Rgba<u8>> {
     iter::once([0, 0, 0, 0].into())
         .chain((1..=max).map(|count| {
             let alpha = count as f64 / max as f64;
+            // If we simply use alpha here, we get a linear mapping, and a jump from 1 to 2
+            // repetitions is worth as much as a jump from 9 to 10. By transforming alpha via the
+            // cubic function given below, we give more weight to the "early" repetitions by having
+            // a steeper slope, and less weight to later repetitions.
+            // There is no science behind the power 3, others work as well (if you adjust the
+            // sign). It seemed like a decent trade-off though.
+            let alpha = (alpha - 1.0).powi(3) + 1.0;
             let color = gradient.at(1.0 - alpha);
             color.to_rgba8().into()
         }))