From 73d162337c473a013773509ef313863ff3fbb38b Mon Sep 17 00:00:00 2001
From: Eryn Wells <eryn@erynwells.me>
Date: Wed, 21 Nov 2018 08:19:41 -0700
Subject: [PATCH] Attempt to do Phong shading in the fragment shader

---
 Terrain2/Shaders/Shaders.metal | 22 ++++++++++++++++++----
 1 file changed, 18 insertions(+), 4 deletions(-)

diff --git a/Terrain2/Shaders/Shaders.metal b/Terrain2/Shaders/Shaders.metal
index 171280a..5348d42 100644
--- a/Terrain2/Shaders/Shaders.metal
+++ b/Terrain2/Shaders/Shaders.metal
@@ -43,7 +43,7 @@ vertex ColorInOut vertexShader(Vertex in [[stage_in]],
 
     out.position = uniforms.projectionMatrix * eyeCoords;
     out.eyeCoords = eyeCoords;
-    out.normal = in.normal;
+    out.normal = normalize(in.normal);
     out.texCoord = in.texCoord;
 
     return out;
@@ -53,10 +53,24 @@ fragment float4 fragmentShader(ColorInOut in [[stage_in]],
                                constant Uniforms &uniforms [[buffer(BufferIndexUniforms)]])
 {
     float3 normal = normalize(uniforms.normalMatrix * in.normal);
-    float3 lightDirection = -in.eyeCoords.xyz;
+    float3 lightDirection = normalize(float3(-8, 8, 1) - in.eyeCoords.xyz);
+    float3 viewDirection = normalize(-in.eyeCoords.xyz);
+    float3 reflection = -reflect(lightDirection, normal);
+
+    float4 out;
     float lightDotNormal = dot(normal, lightDirection);
-    float4 color(abs(lightDotNormal) * float3(0.2), 1.0);
-    return color;
+    if (lightDotNormal <= 0.0) {
+        // No color contribution to this pixel.
+        out = float4();
+    } else {
+        float3 color = 0.8 * lightDotNormal * float3(0.6);
+        float reflectDotViewDirection = dot(reflection, viewDirection);
+        if (reflectDotViewDirection > 0.0) {
+            color += 0.4 * pow(reflectDotViewDirection, 10) * float3(0, 0, 1);
+        }
+        out = float4(color, 1);
+    }
+    return out;
 }
 
 #pragma mark - Normal Shaders