From 80cfd4e0d5e928c2ffed9c4510441fb950908665 Mon Sep 17 00:00:00 2001
From: Dan Goodliffe <dan@randomdan.homeip.net>
Date: Wed, 28 Dec 2022 15:13:01 +0000
Subject: Initial support for multiple shadow maps in the same texture

---
 gfx/gl/shaders/directionalLight.fs | 38 +++++++++++++++++++++++++++++++-------
 1 file changed, 31 insertions(+), 7 deletions(-)

(limited to 'gfx/gl/shaders/directionalLight.fs')

diff --git a/gfx/gl/shaders/directionalLight.fs b/gfx/gl/shaders/directionalLight.fs
index d1e60ee..fa1e38d 100644
--- a/gfx/gl/shaders/directionalLight.fs
+++ b/gfx/gl/shaders/directionalLight.fs
@@ -1,6 +1,8 @@
 #version 330 core
 #extension GL_ARB_shading_language_420pack : enable
 
+const int MAX_MAPS = 3;
+
 out vec3 FragColor;
 
 in vec2 TexCoords;
@@ -11,17 +13,39 @@ layout(binding = 2) uniform sampler2D shadowMap;
 
 uniform vec3 lightDirection;
 uniform vec3 lightColour;
-uniform mat4 lightViewProjection;
+uniform mat4 lightViewProjection[MAX_MAPS];
+uniform vec4 shadowMapRegion[MAX_MAPS];
+uniform uint lightViewProjectionCount;
+
+const vec3 e1 = vec3(-1, -1, -1), e2 = vec3(1, 1, 1);
+
+float
+insideShadowCube(vec3 v)
+{
+	const vec3 s = step(e1, v) - step(e2, v);
+	return s.x * s.y * s.z;
+}
+
+float
+isShaded(vec3 Position)
+{
+	for (uint m = 0u; m < lightViewProjectionCount; m++) {
+		vec3 PositionInLightSpace = (lightViewProjection[m] * vec4(Position, 1.0f)).xyz;
+		const float inside = insideShadowCube(PositionInLightSpace);
+		if (inside > 0) {
+			const float lightSpaceDepth
+					= texture(shadowMap, PositionInLightSpace.xy * shadowMapRegion[m].xy + shadowMapRegion[m].zw).r;
+			return step(lightSpaceDepth, PositionInLightSpace.z * .5 + .5);
+		}
+	}
+	return 0;
+}
 
 void
 main()
 {
 	const vec3 Position = texture(gPosition, TexCoords).xyz;
-	const vec3 PositionInLightSpace = ((lightViewProjection * vec4(Position, 1.0f)) * 0.5 + 0.5).xyz;
-	const float lightSpaceDepth = texture(shadowMap, PositionInLightSpace.xy).r;
-	if (lightSpaceDepth < PositionInLightSpace.z) {
-		discard;
-	}
 	const vec3 Normal = texture(gNormal, TexCoords).rgb;
-	FragColor = max(dot(-lightDirection, Normal) * lightColour, 0);
+	const float shaded = isShaded(Position);
+	FragColor = (1 - shaded) * max(dot(-lightDirection, Normal) * lightColour, 0);
 }
-- 
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