From b254e5b7ba46cf89e0a77043e4f8ed83c593e5eb Mon Sep 17 00:00:00 2001
From: rdb <git@rdb.name>
Date: Wed, 2 Nov 2022 20:49:43 +0100
Subject: [PATCH] assimp: Support importing alpha mode from glTF files

---
 pandatool/src/assimp/assimpLoader.cxx | 19 +++++++++++++++++++
 1 file changed, 19 insertions(+)

diff --git a/pandatool/src/assimp/assimpLoader.cxx b/pandatool/src/assimp/assimpLoader.cxx
index 5725bf85a8..0a5e84fa94 100644
--- a/pandatool/src/assimp/assimpLoader.cxx
+++ b/pandatool/src/assimp/assimpLoader.cxx
@@ -21,9 +21,11 @@
 #include "geomTriangles.h"
 #include "pnmFileTypeRegistry.h"
 #include "pnmImage.h"
+#include "alphaTestAttrib.h"
 #include "materialAttrib.h"
 #include "textureAttrib.h"
 #include "cullFaceAttrib.h"
+#include "transparencyAttrib.h"
 #include "ambientLight.h"
 #include "directionalLight.h"
 #include "spotlight.h"
@@ -43,6 +45,10 @@
 
 #include <assimp/postprocess.h>
 
+#ifndef AI_MATKEY_GLTF_ALPHAMODE
+#define AI_MATKEY_GLTF_ALPHAMODE "$mat.gltf.alphaMode", 0, 0
+#endif
+
 using std::ostringstream;
 using std::stringstream;
 using std::string;
@@ -502,6 +508,19 @@ load_material(size_t index) {
     }
   }
 
+  // Alpha mode.
+  aiString alpha_mode;
+  if (AI_SUCCESS == mat.Get(AI_MATKEY_GLTF_ALPHAMODE, alpha_mode)) {
+    if (strcmp(alpha_mode.C_Str(), "MASK") == 0) {
+      PN_stdfloat cutoff = 0.5;
+      mat.Get(AI_MATKEY_GLTF_ALPHACUTOFF, cutoff);
+      state = state->add_attrib(AlphaTestAttrib::make(AlphaTestAttrib::M_greater_equal, cutoff));
+    }
+    else if (strcmp(alpha_mode.C_Str(), "BLEND") == 0) {
+      state = state->add_attrib(TransparencyAttrib::make(TransparencyAttrib::M_alpha));
+    }
+  }
+
   // And let's not forget the textures!
   CPT(TextureAttrib) tattr = DCAST(TextureAttrib, TextureAttrib::make());
   CPT(TexMatrixAttrib) tmattr;