tinygltf

GLM is a header-only C++ mathematics library designed for graphics software. It is based on the OpenGL Shading Language (GLSL) specifications, meaning it uses the same naming conventions and functionality as GLSL. This makes it highly intuitive for developers familiar with GLSL to use in C++.

Key features include:

• GLSL Compatibility: Classes and functions mirror GLSL.
• Extension System: Provides extended capabilities like matrix transformations, quaternions, data packing, random numbers, and noise using GLSL-style extension conventions.
• Versatility: While optimized for OpenGL, it is suitable for software rendering (raytracing/rasterisation), image processing, and physics simulations.
• Zero Dependencies: A platform-independent, header-only library.

NanoSG uses two primary abstractions to manage a scene graph:

• Node: Represents a node in the scene graph. It can be a transformation node (created by passing nullptr to the Node constructor) or a Mesh (shape) node. Nodes can contain multiple children.
• Scene: Acts as the container for root nodes and provides the interface for ray intersection testing.

To use NanoSG in a user application, you must implement specific classes that the library expects for traversal:

Mesh class

The example assumes meshes are composed of triangles. You must implement the following method for Scene::Traversal:

/// Get the geometric normal and the shading normal at `face_idx' th face.
///
template<typename T>
void GetNormal(T Ng[3], T Ns[3], const unsigned int face_idx, const T u, const T v) const;

Intersection class

You must provide a class that represents intersection (hit) information.

GLM supports GLSL-style precision qualifiers (lowp, mediump, highp) using a prefix syntax on the type names. This allows trading precision for performance. By default, all types use high precision.

To use these, prefix the type name (e.g., lowp_vec4, mediump_vec4, highp_vec4).

#include <glm/glm.hpp>

ivec3 foo(const vec4 & v)
{
    highp_vec4 a = v;
    mediump_vec4 b = a;
    lowp_ivec3 c = glm::ivec3(b);
    return c;
}

Memory Management

Scene and Node do not create copies of asset data (such as vertices or indices). The user is responsible for managing the lifetime and memory of all scene assets.

Transformations

Transformations are calculated using the following hierarchy: M' = parent_xform x local_xform x local_pivot

In the ExtensionMap for v2, JSON number values are stored as tinygltf::Value objects.

• IsNumber() returns true for both integer and floating-point values.
• To retrieve a floating-point value, use the GetNumberAsDouble() method.

When integrating GLM into your project, follow these best practices to avoid common issues:

• Avoid using namespace glm;: GLM is based on GLSL, which uses common tokens for types and functions. Using the namespace globally can cause name collisions with other libraries or the standard library.
• Define NOMINMAX on Windows: If you are using Windows headers, define NOMINMAX before including them. This prevents the Windows min and max macros from interfering with GLM.
• Use Radians for Angles: Since GLM 0.9.6, all angular functions (like rotate or perspective) expect angles in radians, not degrees.
• Handle Domain Errors: Be aware that certain functions (like glm::normalize) may crash if passed invalid input (e.g., a zero vector), as this is treated as a domain error similar to the C++ standard library.

The glview example is a simple OpenGL viewer for glTF geometry. To build it on MacOSX or Linux, you need premake5 (alpha12 or later), GLEW, and glfw3.

If glfw3 is not found by pkg-config, you must manually set the PKG_CONFIG_PATH before running the build commands.

# optional. set pkg-config path to find glfw3
$ export PKG_CONFIG_PATH=/path/to/pkgconfig

> premake4 gmake
$ make

To build the basic glTF viewer example on Linux or macOS, you must have glew, glfw3, and premake5 installed. Use premake5 to generate the Makefiles and then run make to compile the project.

$ premake5 gmake
$ make