From 9187edcd45e97efd5b4d699c071bc1530f298d54 Mon Sep 17 00:00:00 2001
From: David Thompson <dthompson2@worcester.edu>
Date: Sat, 8 May 2021 09:00:26 -0400
Subject: graphics: model: Add basic alpha mode support for glTF models.

---
 data/shaders/pbr-frag.glsl | 22 ++++++++++++++++++++++
 1 file changed, 22 insertions(+)

(limited to 'data/shaders/pbr-frag.glsl')

diff --git a/data/shaders/pbr-frag.glsl b/data/shaders/pbr-frag.glsl
index ce252ab..5b21fe1 100644
--- a/data/shaders/pbr-frag.glsl
+++ b/data/shaders/pbr-frag.glsl
@@ -15,6 +15,7 @@ struct Material {
   vec3 emissiveFactor;
   bool emissiveTextureEnabled;
   int emissiveTexcoord;
+  int alphaMode;
   float alphaCutoff;
 };
 
@@ -49,6 +50,25 @@ vec4 sampleTexture(sampler2D tex, bool enabled, int texcoord, vec3 factor, vec4
   }
 }
 
+vec4 applyAlpha(vec4 color) {
+  // Apply alpha mode.
+  if(material.alphaMode == 0) {
+    return vec4(color.xyz, 1.0);
+  } else if(material.alphaMode == 1) {
+    if(color.a >= material.alphaCutoff) {
+      return vec4(color.xyz, 1.0);
+    } else {
+      discard;
+    }
+  } else if(material.alphaMode == 2) {
+    if(color.a <= 0.005) {
+      discard;
+    } else {
+      return color;
+    }
+  }
+}
+
 void main(void) {
   vec4 finalColor = sampleTexture(baseColorTexture,
                                   material.baseColorTextureEnabled,
@@ -77,6 +97,8 @@ void main(void) {
                               material.emissiveTexcoord,
                               material.emissiveFactor,
                               vec4(0.0, 0.0, 0.0, 0.0));
+  finalColor = applyAlpha(finalColor);
+
 #ifdef GLSL330
   fragColor = finalColor;
 #else
-- 
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