Fix view/accessor offset and invariants; fix loading of Flight Helmet

1 files changed, 19 insertions, 15 deletions

diff --git a/src/asset/model.c b/src/asset/model.c
index a97d20e..b5c6b0d 100644
--- a/src/asset/model.c
+++ b/src/asset/model.c
@@ -1030,7 +1030,6 @@ static bool load_meshes(
         const cgltf_attribute*   attrib       = &prim->attributes[a];
         const cgltf_accessor*    accessor     = attrib->data;
         const cgltf_buffer_view* view         = accessor->buffer_view;
-        const cgltf_size         offset       = accessor->offset + view->offset;
         const cgltf_size         buffer_index = view->buffer - data->buffers;
 
         assert(buffer_index < data->buffers_count);
@@ -1120,12 +1119,20 @@ static bool load_meshes(
           break;
         }
 
-#define CONFIGURE_BUFFER(buf)         \
-  if (buf) {                          \
-    buf->buffer       = buffer;       \
-    buf->offset_bytes = offset;       \
-    buf->size_bytes   = view->size;   \
-    buf->stride_bytes = view->stride; \
+        // See comments here for accessor/view/buffer invariants:
+        //   https://github.com/KhronosGroup/glTF-Sample-Assets/issues/242
+        // Gfx only has Buffer and BufferView, not accessors. We must combine
+        // the glTF's accessor and view offsets correctly.
+        const cgltf_size offset     = accessor->offset + view->offset;
+        const cgltf_size size_bytes = view->size - accessor->offset;
+
+#define CONFIGURE_BUFFER(buf)            \
+  if (buf) {                             \
+    buf->buffer       = buffer;          \
+    buf->offset_bytes = offset;          \
+    buf->size_bytes   = size_bytes;      \
+    buf->stride_bytes = view->stride;    \
+    buf->count        = accessor->count; \
   }
         CONFIGURE_BUFFER(buffer_view_2d);
         CONFIGURE_BUFFER(buffer_view_3d);
@@ -1160,14 +1167,11 @@ static bool load_meshes(
       // either 2d or 3d positions but not both, here we can perform addition
       // to compute the total number of vertices.
       geometry_desc.num_verts =
-          (geometry_desc.positions2d.size_bytes / sizeof(vec2)) +
-          (geometry_desc.positions3d.size_bytes / sizeof(vec3));
-
-#define CHECK_COUNT(buffer_view, type, num_components)                 \
-  if (geometry_desc.buffer_view.buffer) {                              \
-    assert(                                                            \
-        (geometry_desc.buffer_view.size_bytes /                        \
-         (num_components * sizeof(type))) == geometry_desc.num_verts); \
+          geometry_desc.positions2d.count + geometry_desc.positions3d.count;
+
+#define CHECK_COUNT(buffer_view, type, num_components)                  \
+  if (geometry_desc.buffer_view.buffer) {                               \
+    assert(geometry_desc.buffer_view.count == geometry_desc.num_verts); \
   }
 
       // Check that the number of vertices is consistent across all vertex