From ca3d8038cf7eca5d6e66e0f0d40c00a2143fd78f Mon Sep 17 00:00:00 2001
From: Dzmitry Malyshau <kvarkus@gmail.com>
Date: Thu, 24 Oct 2019 12:27:10 -0400
Subject: [PATCH] [rs] Fix shadow sampling outside of the positive hemisphere

---
 wgpu/examples/shadow/forward.frag | 21 ++++++++++++++-------
 1 file changed, 14 insertions(+), 7 deletions(-)

diff --git a/wgpu/examples/shadow/forward.frag b/wgpu/examples/shadow/forward.frag
index 7af5dbdc7f..fdd587ae6d 100644
--- a/wgpu/examples/shadow/forward.frag
+++ b/wgpu/examples/shadow/forward.frag
@@ -28,6 +28,19 @@ layout(set = 1, binding = 0) uniform Entity {
     vec4 u_Color;
 };
 
+float fetch_shadow(int light_id, vec4 homogeneous_coords) {
+    if (homogeneous_coords.w <= 0.0) {
+        return 1.0;
+    }
+    // compute texture coordinates for shadow lookup
+    vec4 light_local = vec4(
+        (homogeneous_coords.xy/homogeneous_coords.w + 1.0) / 2.0,
+        light_id,
+        homogeneous_coords.z / homogeneous_coords.w
+    );
+    // do the lookup, using HW PCF and comparison
+    return texture(sampler2DArrayShadow(t_Shadow, s_Shadow), light_local);
+}
 
 void main() {
     vec3 normal = normalize(v_Normal);
@@ -37,13 +50,7 @@ void main() {
     for (int i=0; i<int(u_NumLights.x) && i<MAX_LIGHTS; ++i) {
         Light light = u_Lights[i];
         // project into the light space
-        vec4 light_local = light.proj * v_Position;
-        // compute texture coordinates for shadow lookup
-        light_local.xy = (light_local.xy/light_local.w + 1.0) / 2.0;
-        light_local.w = light_local.z / light_local.w;
-        light_local.z = i;
-        // do the lookup, using HW PCF and comparison
-        float shadow = texture(sampler2DArrayShadow(t_Shadow, s_Shadow), light_local);
+        float shadow = fetch_shadow(i, light.proj * v_Position);
         // compute Lambertian diffuse term
         vec3 light_dir = normalize(light.pos.xyz - v_Position.xyz);
         float diffuse = max(0.0, dot(normal, light_dir));