From 7c54677acd968fa1333c0cec97911b61dc2370f5 Mon Sep 17 00:00:00 2001
From: "Arthur Brainville (Ybalrid)" <ybalrid@ybalrid.info>
Date: Mon, 19 Feb 2018 18:01:53 +0100
Subject: [PATCH] Now load index buffer

Added some template infrastructure to read arrays where type is defined by a value.

Signed-off by: Arthur Brainville (Ybalrid) <ybalrid@ybalrid.info>
---
 examples/raytrace/gltf-loader.cc | 135 +++++++++++++++++++++++++++++--
 1 file changed, 128 insertions(+), 7 deletions(-)

diff --git a/examples/raytrace/gltf-loader.cc b/examples/raytrace/gltf-loader.cc
index 5ab5ac7..91434b2 100644
--- a/examples/raytrace/gltf-loader.cc
+++ b/examples/raytrace/gltf-loader.cc
@@ -1,9 +1,9 @@
 #include "gltf-loader.h"
 
 #include <iostream>
-
+#include <memory>  // c++11
 #define TINYGLTF_IMPLEMENTATION
-#include "tiny_gltf.h"
+#include <tiny_gltf.h>
 
 namespace example {
 
@@ -13,6 +13,56 @@ static std::string GetFilePathExtension(const std::string &FileName) {
   return "";
 }
 
+template <typename T>
+struct arrayAdapter {
+  unsigned char *dataPtr;
+  const size_t elemCount;
+  const size_t stride;
+  arrayAdapter(unsigned char *ptr, size_t count, size_t byte_stride = 1)
+      : dataPtr(ptr), elemCount(count), stride(byte_stride) {}
+
+  T operator[](size_t pos) {
+    if (pos >= elemCount)
+      throw std::out_of_range(
+          "Tried to access beyond the last element of an array adapter");
+    return *(reinterpret_cast<T *>(dataPtr + pos * stride));
+  }
+};
+
+struct intArrayBase {
+  virtual int operator[](size_t) = 0;
+  virtual size_t size() const = 0;
+};
+
+struct floatArrayBase {
+  virtual float operator[](size_t) = 0;
+  virtual size_t size() const = 0;
+};
+
+template <class T>
+struct intArray : public intArrayBase {
+  arrayAdapter<T> adapter;
+
+  intArray(const arrayAdapter<T> &a) : adapter(a) {}
+  int operator[](size_t position) override {
+    return static_cast<int>(adapter[position]);
+  }
+
+  size_t size() const override { return adapter.elemCount; }
+};
+
+template <class T>
+struct floatArray : public floatArrayBase {
+  arrayAdapter<T> adapter;
+
+  floatArray(const arrayAdapter<T> &a) : adapter(a) {}
+  float operator[](size_t position) override {
+    return static_cast<float>(adapter[position]);
+  }
+
+  size_t size() const override { return adapter.elemCount; }
+};
+
 ///
 /// Loads glTF 2.0 mesh
 ///
@@ -46,8 +96,6 @@ bool LoadGLTF(const std::string &filename, float scale,
     return false;
   }
 
-  std::cerr << "LoadGLTF() function is not yet implemented!" << std::endl;
-
   std::cout << "loaded glTF file has:\n"
             << model.accessors.size() << " accessors\n"
             << model.animations.size() << " animations\n"
@@ -67,11 +115,84 @@ bool LoadGLTF(const std::string &filename, float scale,
   for (const auto &gltfMesh : model.meshes) {
     std::cout << "Current mesh has " << gltfMesh.primitives.size()
               << " primitives:\n";
+
+    Mesh<float> loadedMesh(sizeof(float) * 3);
+    loadedMesh.name = gltfMesh.name;
     for (const auto &meshPrimitive : gltfMesh.primitives) {
+      // get access to the indices
+      std::unique_ptr<intArrayBase> indicesArray = nullptr;
+
+      auto &indicesAccessor = model.accessors[meshPrimitive.indices];
+      auto &bufferView = model.bufferViews[indicesAccessor.bufferView];
+      auto &buffer = model.buffers[bufferView.buffer];
+      unsigned char *dataAddress = buffer.data.data() + bufferView.byteOffset +
+                                   indicesAccessor.byteOffset;
+      const auto byteStride = indicesAccessor.ByteStride(bufferView);
+      const auto count = indicesAccessor.count;
+
+      switch (indicesAccessor.componentType) {
+        case TINYGLTF_COMPONENT_TYPE_BYTE:
+          indicesArray = std::unique_ptr<intArray<char> >(new intArray<char>(
+              arrayAdapter<char>(dataAddress, count, byteStride)));
+          break;
+
+        case TINYGLTF_COMPONENT_TYPE_UNSIGNED_BYTE:
+          indicesArray = std::unique_ptr<intArray<unsigned char> >(
+              new intArray<unsigned char>(
+                  arrayAdapter<unsigned char>(dataAddress, count, byteStride)));
+          break;
+
+        case TINYGLTF_COMPONENT_TYPE_SHORT:
+          indicesArray = std::unique_ptr<intArray<short> >(new intArray<short>(
+              arrayAdapter<short>(dataAddress, count, byteStride)));
+          break;
+
+        case TINYGLTF_COMPONENT_TYPE_UNSIGNED_SHORT:
+          indicesArray = std::unique_ptr<intArray<unsigned short> >(
+              new intArray<unsigned short>(arrayAdapter<unsigned short>(
+                  dataAddress, count, byteStride)));
+          break;
+
+        case TINYGLTF_COMPONENT_TYPE_INT:
+          indicesArray = std::unique_ptr<intArray<int> >(new intArray<int>(
+              arrayAdapter<int>(dataAddress, count, byteStride)));
+          break;
+
+        case TINYGLTF_COMPONENT_TYPE_UNSIGNED_INT:
+          indicesArray = std::unique_ptr<intArray<unsigned int> >(
+              new intArray<unsigned int>(
+                  arrayAdapter<unsigned int>(dataAddress, count, byteStride)));
+          break;
+        default:
+          break;
+      }
+
+      if (indicesArray)
+        for (size_t i(0); i < indicesArray->size(); ++i) {
+          std::cout << (*indicesArray)[i] << " ";
+        }
+
+      std::cout << '\n';
+
       switch (meshPrimitive.mode) {
         case TINYGLTF_MODE_TRIANGLES:  // this is the simpliest case to handle
+
+        {
           std::cout << "Will load a plain old list of trianges\n";
-          break;
+
+          for (const auto &attribute : meshPrimitive.attributes) {
+            if (attribute.first == "POSITION") {
+              std::cout << "found position attribute\n";
+              const auto posAccessor = model.accessors[attribute.second];
+            }
+
+            if (attribute.first == "NORMAL") {
+              std::cout << "found normal attribute\n";
+            }
+          }
+        }
+
+        break;
 
         // Other trigangle based modes
         case TINYGLTF_MODE_TRIANGLE_FAN:
@@ -89,7 +210,7 @@ bool LoadGLTF(const std::string &filename, float scale,
     }
   }
 
+  std::cerr << "LoadGLTF() function is not yet implemented!" << std::endl;
   return false;
 }
-
-}  // namespace example
+}  // namespace example
\ No newline at end of file