From 89edd1878791a77256e170a79c7cf9ecc9f649d8 Mon Sep 17 00:00:00 2001
From: Imbris <imbrisf@gmail.com>
Date: Fri, 28 Jan 2022 22:55:38 -0500
Subject: [PATCH] Dither in nonlinear srgb space and add a few dithering
 related things to the experimental shader options

---
 assets/voxygen/shaders/include/random.glsl   | 10 ++++++++++
 assets/voxygen/shaders/postprocess-frag.glsl | 21 ++++++++++++++++++--
 voxygen/src/render/mod.rs                    |  6 ++++++
 3 files changed, 35 insertions(+), 2 deletions(-)

diff --git a/assets/voxygen/shaders/include/random.glsl b/assets/voxygen/shaders/include/random.glsl
index a3ce9c8137..4330ca3770 100644
--- a/assets/voxygen/shaders/include/random.glsl
+++ b/assets/voxygen/shaders/include/random.glsl
@@ -109,4 +109,14 @@ vec3 smooth_rand(vec3 pos, float lerp_axis) {
     vec3 r1 = rand_perm_3(vec3(pos.x, pos.y, pos.z) + floor(lerp_axis + 1.0));
     return r0 + (r1 - r0) * fract(lerp_axis);
 }
+
+// Transform normal distribution to triangle distribution.
+float norm2tri(float n) {
+   // TODO: compare perf with adding two normal noise distributions
+   bool flip = n > 0.5;
+   n = flip ? 1.0 - n : n;
+   n = sqrt(n / 2.0);
+   n = flip ? 1.0 - n : n;
+   return n;
+}
 #endif
diff --git a/assets/voxygen/shaders/postprocess-frag.glsl b/assets/voxygen/shaders/postprocess-frag.glsl
index 8882f42faf..50059e245c 100644
--- a/assets/voxygen/shaders/postprocess-frag.glsl
+++ b/assets/voxygen/shaders/postprocess-frag.glsl
@@ -282,9 +282,26 @@ void main() {
     }
 #endif
 
+#ifndef EXPERIMENTAL_NODITHER
     // Add a small amount of very cheap dithering noise to remove banding from gradients
-    // TODO: Instead of 256, detect the colour resolution of the display
-    final_color.rgb = max(vec3(0), final_color.rgb - hash_two(uvec2(uv * screen_res.xy)) / 256.0);
+    // TODO: Consider dithering each color channel independently.
+    // TODO: Consider varying dither over time.
+    // TODO: Instead of 255, detect the colour resolution of the color attachment
+    float noise = hash_two(uvec2(uv * screen_res.xy));
+    #ifndef EXPERIMENTAL_NONSRGBDITHER
+        #ifndef EXPERIMENTAL_TRIANGLENOISEDITHER
+            noise = noise - 0.5;
+        #else
+            // TODO: there is something special we have to do to remove bias
+            // on the bounds when using triangle distribution
+            noise = 2.0 * norm2tri(noise) - 1.0;
+        #endif
+        final_color.rgb = srgb_to_linear(linear_to_srgb(final_color.rgb) + noise / 255.0);
+    #else
+        // NOTE: GPU will clamp value
+        final_color.rgb = final_color.rgb - noise / 255.0;
+    #endif
+#endif
 
     tgt_color = vec4(final_color.rgb, 1);
 }
diff --git a/voxygen/src/render/mod.rs b/voxygen/src/render/mod.rs
index e5066f374f..3da8c2f4d8 100644
--- a/voxygen/src/render/mod.rs
+++ b/voxygen/src/render/mod.rs
@@ -447,4 +447,10 @@ pub enum ExperimentalShader {
     Underwarper,
     /// Remove caustics from underwater terrain when shiny water is enabled.
     NoCaustics,
+    /// Don't dither color in post-processing.
+    NoDither,
+    /// Don't use the nonlinear srgb space for dithering color.
+    NonSrgbDither,
+    /// Use triangle PDF noise for dithering instead of uniform noise.
+    TriangleNoiseDither,
 }