From 62285e0569a926948b14c472fb2290d4acedaa51 Mon Sep 17 00:00:00 2001
From: Jelle Raaijmakers <jelle@gmta.nl>
Date: Fri, 17 Feb 2023 17:10:35 +0100
Subject: [PATCH] LibSoftGPU: Use multiplication instead of division for linear
 fog

Sampling profiling shows a reduction of nearly 60% for the linear fog
calculation case.
---
 Userland/Libraries/LibSoftGPU/Device.cpp | 4 +++-
 Userland/Libraries/LibSoftGPU/Device.h   | 1 +
 2 files changed, 4 insertions(+), 1 deletion(-)

diff --git a/Userland/Libraries/LibSoftGPU/Device.cpp b/Userland/Libraries/LibSoftGPU/Device.cpp
index 846ca34c7af..57b32491216 100644
--- a/Userland/Libraries/LibSoftGPU/Device.cpp
+++ b/Userland/Libraries/LibSoftGPU/Device.cpp
@@ -1281,7 +1281,7 @@ ALWAYS_INLINE void Device::shade_fragments(PixelQuad& quad)
         f32x4 factor;
         switch (m_options.fog_mode) {
         case GPU::FogMode::Linear:
-            factor = (m_options.fog_end - quad.fog_depth) / (m_options.fog_end - m_options.fog_start);
+            factor = (m_options.fog_end - quad.fog_depth) * m_one_over_fog_depth;
             break;
         case GPU::FogMode::Exp: {
             auto argument = -m_options.fog_density * quad.fog_depth;
@@ -1555,6 +1555,8 @@ void Device::draw_statistics_overlay(Gfx::Bitmap& target)
 void Device::set_options(GPU::RasterizerOptions const& options)
 {
     m_options = options;
+    if (m_options.fog_enabled)
+        m_one_over_fog_depth = 1.f / (m_options.fog_end - m_options.fog_start);
 }
 
 void Device::set_light_model_params(GPU::LightModelParameters const& lighting_model)
diff --git a/Userland/Libraries/LibSoftGPU/Device.h b/Userland/Libraries/LibSoftGPU/Device.h
index ced6abac168..b53e3246989 100644
--- a/Userland/Libraries/LibSoftGPU/Device.h
+++ b/Userland/Libraries/LibSoftGPU/Device.h
@@ -110,6 +110,7 @@ private:
     Vector<Triangle> m_triangle_list;
     Vector<Triangle> m_processed_triangles;
     Vector<GPU::Vertex> m_clipped_vertices;
+    float m_one_over_fog_depth;
     Array<Sampler, GPU::NUM_TEXTURE_UNITS> m_samplers;
     bool m_samplers_need_texture_staging { false };
     Array<GPU::Light, NUM_LIGHTS> m_lights;