From 3ca3b1daa8cbd63d8ca51d16d90679dcc116f673 Mon Sep 17 00:00:00 2001
From: Lucian Plesea <LPlesea@esri.com>
Date: Wed, 24 Jul 2024 10:47:48 -0700
Subject: [PATCH] Tuned hillshade formula a bit

---
 docs/lerc1dec.wasm | Bin 57586 -> 57618 bytes
 rasterfunk.cpp     |  31 ++++++++++++++-----------------
 2 files changed, 14 insertions(+), 17 deletions(-)

diff --git a/docs/lerc1dec.wasm b/docs/lerc1dec.wasm
index 13d9058405ae6942426eb9e3852bb3081e3e0843..d7e1ba9756b442aba2a0c1ef6d13e567d43134f3 100644
GIT binary patch
delta 156
zcmex#ka^M}<_*UgnHqm@KFK(vpQ%@Va`Hrr&2uMO^BFMJD@ZBGW+`!NFfk}`IdYUa
z{%0)Q;lcn0Z|oOASq=^h6j*1@S7M#~XTGis7am1G1*((d7x2h)ISSx2Y;*mBVg~^D
Ci7jOS

delta 128
zcmbPqi22h&<_*UgnI8Vye3EfSKhs;e$;lHf80$CBnrOqPqQI)ax=4vtK}tb3ONm>9
zi9w0Wk)zD<KVzXIbB-fZnWIDYj>-NDR3#lbN)&mR>VfLHFk}ryK%xR@+BVN$Q0xEz
D&-Ezo

diff --git a/rasterfunk.cpp b/rasterfunk.cpp
index 4931edc..7592833 100644
--- a/rasterfunk.cpp
+++ b/rasterfunk.cpp
@@ -56,7 +56,8 @@ int hillshade(float *data, size_t sz, double pixel_size, double sun_angle, uint3
     constexpr int TILESIZE(256);
     constexpr int DATATILESIZE(257);
     constexpr uint32_t ALPHA(0xff000000);
-
+    constexpr auto base(32.0); // baseline brightness
+    constexpr auto rescale((256 - base) / 256); // brightness rescale factor
     for (int y = 0; y < TILESIZE; y++)
     {
         for (int x = 0; x < TILESIZE; x++)
@@ -66,24 +67,20 @@ int hillshade(float *data, size_t sz, double pixel_size, double sun_angle, uint3
             double slope = (rightp - leftp) / 1.41 / pixel_size;
             double normal_angle = std::asin(slope) - sun_angle + M_PI_2;
             double factor = abs(std::cos(normal_angle)); // 0 to 1
-            factor *= factor; // square
-
-            // If the input is grayscale:
-            // uint32_t val = pixels[TILESIZE * y + x] & 0xff; // grayscale byte
-            // val = 64 + val * 3 / 4; // Keep a baseline brightness of 64
-            // val = uint32_t(val * factor);
-            // pixels[TILESIZE * y + x] = (val * 0x10101) | ALPHA;
+            // negative power decrease the effect, positive increase it
+            // -2 is a good value for a subtle effect
+            factor = sqrt(factor);
 
-            uint32_t red = pixels[TILESIZE * y + x] & 0xff;
-            uint32_t green = (pixels[TILESIZE * y + x] >> 8) & 0xff;
-            uint32_t blue = (pixels[TILESIZE * y + x] >> 16) & 0xff;
-            uint32_t alpha = (pixels[TILESIZE * y + x] >> 24) & 0xff;
-            red = (64 + red * 3 / 4) * factor;
-            green = (64 + green * 3 / 4) * factor;
-            blue = (64 + blue * 3 / 4) * factor;
-            alpha = 255;
+            uint32_t val = pixels[TILESIZE * y + x];
+            uint32_t red = val & 0xff;
+            uint32_t green = (val >> 8) & 0xff;
+            uint32_t blue = (val >> 16) & 0xff;
+            uint32_t alpha = (val >> 24) & 0xff;
+            red = (base + rescale * red) * factor;
+            green = (base + rescale * green) * factor;
+            blue = (base + rescale * blue) * factor;
 
-            pixels[TILESIZE * y + x] = (alpha << 24) | (blue << 16) | (green << 8) | red;
+            pixels[TILESIZE * y + x] = ALPHA | (blue << 16) | (green << 8) | red;
         }
     }
     return 1;