From 5a7b53833d78a1d68313a59943aa11c5a8029973 Mon Sep 17 00:00:00 2001
From: a dinosaur <dino@a-dinosaur.com>
Date: Mon, 19 Aug 2024 00:05:53 +1000
Subject: [PATCH] specular highlights (blinn-phong)

---
 Sources/Voxelotl/Game.swift     |  5 +++--
 Sources/Voxelotl/Renderer.swift |  6 +++++-
 Sources/Voxelotl/shader.metal   | 16 ++++++++++++----
 Sources/Voxelotl/shadertypes.h  |  4 +++-
 4 files changed, 23 insertions(+), 8 deletions(-)

diff --git a/Sources/Voxelotl/Game.swift b/Sources/Voxelotl/Game.swift
index a0976f9..4d39b07 100644
--- a/Sources/Voxelotl/Game.swift
+++ b/Sources/Voxelotl/Game.swift
@@ -64,6 +64,7 @@ class Game: GameDelegate {
 
   func draw(_ renderer: Renderer, _ time: GameTime) {
     let totalTime = Float(time.total.asFloat)
+    let cubeSpeedMul: Float = 0.1
 
     var instances: [Instance] = boxes.map {
       Instance(
@@ -73,9 +74,9 @@ class Game: GameDelegate {
     }
     instances.append(
       Instance(
-        position: .init(0, sin(totalTime * 1.5) * 0.5, -2) * 2,
+        position: .init(0, sin(totalTime * 1.5 * cubeSpeedMul) * 0.5, -2) * 2,
         scale:    .init(repeating: 0.5),
-        rotation: .init(angle: totalTime * 3.0, axis: .init(0, 1, 0)),
+        rotation: .init(angle: totalTime * 3.0 * cubeSpeedMul, axis: .init(0, 1, 0)),
         color:    .init(r: 0.5, g: 0.5, b: 1).linear))
     renderer.batch(instances: instances, camera: self.camera)
   }
diff --git a/Sources/Voxelotl/Renderer.swift b/Sources/Voxelotl/Renderer.swift
index 01b886f..278f255 100644
--- a/Sources/Voxelotl/Renderer.swift
+++ b/Sources/Voxelotl/Renderer.swift
@@ -343,7 +343,11 @@ public class Renderer {
     assert(instances.count < 28)
 
     var vertUniforms = VertexShaderUniforms(projView: camera.viewProjection)
-    var fragUniforms = FragmentShaderUniforms(directionalLight: normalize(.init(0.75, -1, 0.5)))
+    var fragUniforms = FragmentShaderUniforms(
+      cameraPosition: camera.position,
+      directionalLight: normalize(.init(0.75, -1, 0.5)),
+      specularColor: SIMD4(Color(rgba8888: 0x7F7F7F00).linear),
+      specularIntensity: 50)
     let instances = instances.map { (instance: Instance) -> VertexShaderInstance in
       let model =
         .translate(instance.position) *
diff --git a/Sources/Voxelotl/shader.metal b/Sources/Voxelotl/shader.metal
index de9d58e..30ba338 100644
--- a/Sources/Voxelotl/shader.metal
+++ b/Sources/Voxelotl/shader.metal
@@ -4,6 +4,7 @@
 
 struct FragmentInput {
   float4 position [[position]];
+  float3 world;
   float3 normal;
   float2 texCoord;
   half4 color;
@@ -18,10 +19,10 @@ vertex FragmentInput vertexMain(
 ) {
   auto position = vtx[vertexID].position;
   auto world = i[instanceID].model * position;
-  auto ndc = u.projView * world;
 
   FragmentInput out;
-  out.position = ndc;
+  out.position = u.projView * world;
+  out.world    = world.xyz;
   out.color    = half4(i[instanceID].color) / 255.0;
   out.normal   = (i[instanceID].normalModel * vtx[vertexID].normal).xyz;
   out.texCoord = vtx[vertexID].texCoord;
@@ -36,11 +37,18 @@ fragment half4 fragmentMain(
   constexpr metal::sampler sampler(metal::address::repeat, metal::filter::nearest);
   auto normal = metal::normalize(in.normal);
 
-  float lambert = metal::dot(normal, -u.directionalLight);
+  auto lightVec = -u.directionalLight;
+  float lambert = metal::dot(normal, lightVec);
   float diffuse = metal::max(0.0, lambert);
 
+  auto eyeVector = metal::normalize(u.cameraPosition - in.world);
+  auto halfDir = metal::normalize(lightVec + eyeVector);
+  float specularAngle = metal::max(0.0, metal::dot(halfDir, normal));
+  float specularTerm = metal::pow(specularAngle, u.specularIntensity);
+  half4 specularAmount = specularTerm * metal::smoothstep(0, 2, lambert * u.specularIntensity);
+
   half4 albedo = texture.sample(sampler, in.texCoord);
   albedo *= in.color;
 
-  return albedo * diffuse;
+  return albedo * diffuse + half4(u.specularColor) * specularAmount;
 }
diff --git a/Sources/Voxelotl/shadertypes.h b/Sources/Voxelotl/shadertypes.h
index 1448c47..e84a541 100644
--- a/Sources/Voxelotl/shadertypes.h
+++ b/Sources/Voxelotl/shadertypes.h
@@ -37,7 +37,9 @@ typedef NS_ENUM(NSInteger, FragmentShaderInputIdx) {
 };
 
 typedef struct {
-  vector_float3 directionalLight;
+  vector_float3 cameraPosition, directionalLight;
+  vector_float4 specularColor;
+  float specularIntensity;
 } FragmentShaderUniforms;
 
 #endif//SHADERTYPES_H