SharpGLTF/src/SharpGLTF.Runtime

# SharpGLTF.Runtime

This namespace contains some utility classes to help rendering glTF models with client graphics engines which typically use GPU accelerated resources.

The process is this; first of all we load a glTF model:

var model = SharpGLTF.Schema2.ModelRoot.Load("model.gltf");

Now, lets say you have an AwesomeEngine which defines an AwesomeMesh that is the equivalent of a glTF Mesh, so for each logical glTF Mesh we find in Model.LogicalMeshes, we create the equivalent AwesomeMesh:

var gpuMeshes = new AwesomeMesh[model.LogicalMeshes.Count];
for(int i=0; i < model.LogicalMeshes.Count; ++i)
{
    gpuMeshes[i] = new AwesomeMesh(model.LogicalMeshes[i]);
}

Next, we create a scene template from the default glTF scene:

// a SceneTemplate is an immutable object that
// represent the resource asset in memory

var modelTemplate = SharpGLTF.Runtime.SceneTemplate(model.DefaultScene,true);

// SceneInstances are lightweight objects that reference
// the original template and can be animated separately.
// each SceneInstance can be set to a specific animation/time,
// and individual nodes can be edited at will, without affecting
// the state of sibling instances.

var inst1 = modelTemplate.CreateInstance();
    inst1.SetAnimationFrame("Walking", 2.17f);
    
var inst2 = modelTemplate.CreateInstance();
    inst2.SetAnimationFrame("Running", 3.523f);
    
var inst3 = modelTemplate.CreateInstance();
    inst3.SetAnimationFrame("Running", 1.32f);
    inst3.SetWorldMatrix("Head", Matrix.LookAt(...) ); // example of manually setting a single node matrix
    
    RenderInstance(inst1, Matrix4x4.CreateTranslation(-10,0,0));
    RenderInstance(inst2, Matrix4x4.CreateTranslation(  0,0,0));
    RenderInstance(inst3, Matrix4x4.CreateTranslation( 10,0,0));

Finally, we render the instances like this:

void RenderInstance(SharpGLTF.Runtime.SceneInstance modelInstance, Matrix4x4 modelMatrix)
{
    foreach(var drawable in modelInstance.DrawableInstances)
    {
        var gpuMesh = gpuMeshes[drawable.Template.LogicalMeshIndex];

        if (drawable.Transform is SharpGLTF.Transforms.RigidTransform statXform)
        {
            AwesomeEngine.DrawRigidMesh(gpuMesh, modelMatrix, statXform.WorldMatrix);
        }

        if (drawable.Transform is SharpGLTF.Transforms.SkinnedLogicalMeshIndexTransform skinXform)
        {
            AwesomeEngine.DrawSkinnedMesh(gpuMesh, modelMatrix, skinXform.SkinMatrices);
        }
    }
}