Linearize light colors on the CPU

CHANGELOG.md

@@ -58,6 +58,7 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 - The ability limit for non-humanoids has been removed
 - Improved running, wielding, and riding animations
 - Fixed offset of items carried on backs when wearing cloaks and backpacks
+- Linearize light colors on the CPU rather than in shaders on the GPU
 
 ### Removed
 - Medium and large potions from all loot tables

assets/voxygen/shaders/include/light.glsl

@@ -84,7 +84,7 @@ vec3 light_at(vec3 wpos, vec3 wnorm) {
 
         float strength = attenuation_strength(difference);
 
-        vec3 color = srgb_to_linear(L.light_col.rgb) * strength;
+        vec3 color = L.light_col.rgb * strength;
 
         light += color * (max(0, max(dot(normalize(difference), wnorm), 0.15)) + LIGHT_AMBIANCE);
     }

assets/voxygen/shaders/include/point_glow.glsl

@@ -33,7 +33,7 @@ void apply_point_glow_light(Light L, vec3 wpos, vec3 dir, float max_dist, inout
         strength *= clamp(cam_dist_2 / 9.0, 0.25, 1.0);
     #endif
 
-    vec3 light_color = srgb_to_linear(L.light_col.rgb) * strength;
+    vec3 light_color = L.light_col.rgb * strength;
 
     const float LIGHT_AMBIANCE = 0.025;
     color += light_color

common/benches/color_benchmark.rs

@@ -1,13 +1,13 @@
 use criterion::{black_box, criterion_group, criterion_main, Criterion};
 
 use vek::*;
-use veloren_common::util::{linear_to_srgb, srgb_to_linear};
+use veloren_common::util::{linear_to_srgb, srgb_to_linear_fast};
 
 fn criterion_benchmark(c: &mut Criterion) {
     let mut c = c.benchmark_group("color");
     c.bench_function("srgb to linear (0.5, 0.1, 0.5)", |b| {
         b.iter(|| {
-            black_box(srgb_to_linear(black_box(Rgb::new(0.5, 0.1, 0.5))));
+            black_box(srgb_to_linear_fast(black_box(Rgb::new(0.5, 0.1, 0.5))));
         })
     });
     c.bench_function("linear to srgb (0.5, 0.1, 0.5)", |b| {

common/src/util/color.rs

@@ -1,8 +1,9 @@
 use vek::{Mat3, Rgb, Rgba, Vec3};
 
+/// This function is optimized for speed over perfect accuracy
 #[inline(always)]
 #[allow(clippy::excessive_precision)]
-pub fn srgb_to_linear(col: Rgb<f32>) -> Rgb<f32> {
+pub fn srgb_to_linear_fast(col: Rgb<f32>) -> Rgb<f32> {
     col.map(|c| {
         if c <= 0.104 {
             c * 0.08677088
@@ -12,6 +13,19 @@ pub fn srgb_to_linear(col: Rgb<f32>) -> Rgb<f32> {
     })
 }
 
+/// directly converted from 'vec3 srgb_to_linear(vec3 srgb)' function in
+/// 'srgb.glsl'
+#[inline(always)]
+pub fn srgb_to_linear(col: Rgb<f32>) -> Rgb<f32> {
+    col.map(|c| {
+        if c <= 0.04045 {
+            c / 12.92
+        } else {
+            f32::powf((c + 0.055) / 1.055, 2.4)
+        }
+    })
+}
+
 #[inline(always)]
 #[allow(clippy::excessive_precision)]
 pub fn linear_to_srgb(col: Rgb<f32>) -> Rgb<f32> {
@@ -29,7 +43,7 @@ pub fn linear_to_srgb(col: Rgb<f32>) -> Rgb<f32> {
 
 #[inline(always)]
 pub fn srgba_to_linear(col: Rgba<f32>) -> Rgba<f32> {
-    Rgba::from_translucent(srgb_to_linear(Rgb::from(col)), col.a)
+    Rgba::from_translucent(srgb_to_linear_fast(Rgb::from(col)), col.a)
 }
 
 #[inline(always)]
@@ -133,7 +147,7 @@ pub fn xyy_to_rgb(xyy: Vec3<f32>) -> Rgb<f32> {
 // TO-DO: speed this up
 #[inline(always)]
 pub fn saturate_srgb(col: Rgb<f32>, value: f32) -> Rgb<f32> {
-    let mut hsv = rgb_to_hsv(srgb_to_linear(col));
+    let mut hsv = rgb_to_hsv(srgb_to_linear_fast(col));
     hsv.y *= 1.0 + value;
     linear_to_srgb(hsv_to_rgb(hsv).map(|e| e.clamp(0.0, 1.0)))
 }
@@ -142,8 +156,8 @@ pub fn saturate_srgb(col: Rgb<f32>, value: f32) -> Rgb<f32> {
 /// other
 #[inline(always)]
 pub fn chromify_srgb(luma: Rgb<f32>, chroma: Rgb<f32>) -> Rgb<f32> {
-    let l = rgb_to_xyy(srgb_to_linear(luma)).z;
+    let l = rgb_to_xyy(srgb_to_linear_fast(luma)).z;
-    let mut xyy = rgb_to_xyy(srgb_to_linear(chroma));
+    let mut xyy = rgb_to_xyy(srgb_to_linear_fast(chroma));
     xyy.z = l;
 
     linear_to_srgb(xyy_to_rgb(xyy).map(|e| e.clamp(0.0, 1.0)))

voxygen/src/render/pipelines/mod.rs

@@ -19,7 +19,7 @@ pub mod ui;
 use super::{Consts, Renderer, Texture};
 use crate::scene::camera::CameraMode;
 use bytemuck::{Pod, Zeroable};
-use common::terrain::BlockKind;
+use common::{terrain::BlockKind, util::srgb_to_linear};
 use std::marker::PhantomData;
 use vek::*;
 
@@ -246,9 +246,12 @@ impl Default for Globals {
 
 impl Light {
     pub fn new(pos: Vec3<f32>, col: Rgb<f32>, strength: f32) -> Self {
+        let linearized_col = srgb_to_linear(col);
+
         Self {
             pos: Vec4::from(pos).into_array(),
-            col: (Rgba::new(col.r, col.g, col.b, 0.0) * strength).into_array(),
+            col: (Rgba::new(linearized_col.r, linearized_col.g, linearized_col.b, 0.0) * strength)
+                .into_array(),
         }
     }
 

voxygen/src/scene/figure/load.rs

@@ -92,12 +92,12 @@ pub fn load_mesh(mesh_name: &str, position: Vec3<f32>) -> BoneMeshes {
 }
 
 fn recolor_grey(rgb: Rgb<u8>, color: Rgb<u8>) -> Rgb<u8> {
-    use common::util::{linear_to_srgb, srgb_to_linear};
+    use common::util::{linear_to_srgb, srgb_to_linear_fast};
 
     const BASE_GREY: f32 = 178.0;
     if rgb.r == rgb.g && rgb.g == rgb.b {
-        let c1 = srgb_to_linear(rgb.map(|e| e as f32 / BASE_GREY));
+        let c1 = srgb_to_linear_fast(rgb.map(|e| e as f32 / BASE_GREY));
-        let c2 = srgb_to_linear(color.map(|e| e as f32 / 255.0));
+        let c2 = srgb_to_linear_fast(color.map(|e| e as f32 / 255.0));
 
         linear_to_srgb(c1 * c2).map(|e| (e.clamp(0.0, 1.0) * 255.0) as u8)
     } else {

voxygen/src/ui/graphic/renderer.rs

@@ -1,6 +1,6 @@
 use common::{
     figure::Segment,
-    util::{linear_to_srgba, srgb_to_linear},
+    util::{linear_to_srgba, srgb_to_linear_fast},
     vol::{FilledVox, IntoFullVolIterator, ReadVol, SizedVol},
 };
 use euc::{buffer::Buffer2d, rasterizer, Pipeline};
@@ -97,7 +97,7 @@ impl Pipeline for Voxel {
         let diffuse = norm.dot(-self.light_dir).max(0.0);
         let brightness = 2.5;
         let light = Rgb::from(*ao_level as f32 / 4.0) * (diffuse + ambiance) * brightness;
-        let color = light * srgb_to_linear(*col);
+        let color = light * srgb_to_linear_fast(*col);
         let position = (self.mvp * Vec4::from_point(*pos)).into_array();
         (position, VsOut(Rgba::from_opaque(color)))
     }