Dynamic Meshes

The article describes operations on dynamic meshes via the code by using methods of the ObjectMeshDynamic claas. This class is used to procedurally create dynamic meshes and modify them in run-time. You can also load an existing mesh as a dynamic one in order to modify it.

• An ObjectMeshDynamic class to edit dynamic meshes via UnigineScript
• A set of samples located in the data/samples/objects/ directory:

Creating a Dynamic Mesh

There are three methods to add a new dynamic mesh:

Creating a New Dynamic Mesh

This chapter describes how to create a new dynamic mesh by allocating memory and adding vertices for a new mesh. You can allocate memory for a moderate number of triangles or for a big number of vertices.

You can create a dynamic mesh from scratch, by adding one triangle after another. This variant is suitable for creating meshes with a moderate number of triangles. To create a new dynamic mesh you should do the following:

1. Reserve a necessary space in a vertex buffer for triangle vertices and add indices for them to the index buffer. This is done by calling one of the following methods: All of these functions allocate memory for polygons of the corresponding form.
3. After each call of the addVertex() function, you can set up properties of the last added vertex manually via calling: All these functions are optional, you can call them as needed.
4. Calculate tangent vectors for all vertices via updateTangents().
5. Calculate a bounding box and a bounding sphere for the created mesh by calling updateBounds().
6. If necessary, you can remove duplicated vertices of the created mesh and optimize it for faster rendering. Use updateIndices() function, for example, if a quad polygon is created via addTriangles(2) (6 vertices are created) instead of an optimized addQuads(1) (4 vertices are created).
Usage Example

Source code (C++)
``````// AppWorldLogic.cpp

#include <UnigineObjects.h>
#include <UnigineEditor.h>

using namespace Unigine;
using namespace Math;

int AppWorldLogic::init() {

// create a dynamic mesh and add it into the editor
ObjectMeshDynamicPtr mesh = ObjectMeshDynamic::create();
mesh->release();

mesh->setWorldTransform(translate(Vec3(0.0f, 0.0f, 2.0f)));
mesh->setMaterial("mesh_base", "*");
mesh->setProperty("surface_base", "*");

// allocate space in a vertex buffer and create vertex indices

// add vertices and assign texture coordinates, if necessary

// calculate tangent vectors
mesh->updateTangents();
// optimize vertex and index buffers, if necessary
//mesh->updateIndices();

// calculate a mesh bounding box
mesh->updateBounds();

return 1;
}``````

Adding a Large Number of Vertices

To create dynamic meshes with a huge number of vertices, it is better to use the more optimized approach: instead of allocating memory in small chunks (which can be costly), all necessary memory is preallocated first and filled with data after that.

1. Allocate space for triangle vertices in an index buffer using allocateIndices().
2. Allocate space for vertices in a vertex buffer using allocateVertex().
5. Follow steps 3-6 described above.
Usage Example

The following example shows how to create a plane by adding vertex by vertex.

Source code (C++)
``````// AppWorldLogic.cpp

#include <UnigineObjects.h>
#include <UnigineEditor.h>

using namespace Unigine;
using namespace Math;

int AppWorldLogic::init() {

// create a dynamic mesh and add it into the editor
ObjectMeshDynamicPtr mesh = ObjectMeshDynamic::create();
mesh->release();

mesh->setWorldTransform(translate(Vec3(0.0f, 0.0f, 2.0f)));
mesh->setMaterial("mesh_base", "*");
mesh->setProperty("surface_base", "*");
// allocate space in index and vertex buffers
mesh->allocateIndices(6);
mesh->allocateVertex(4);
// add indices for created vertices

// calculate tangent vectors
mesh->updateTangents();
// optimize vertex and index buffers, if necessary
//mesh->updateIndices();

// calculate a mesh bounding box
mesh->updateBounds();

return 1;
}``````

Creating a Dynamic Mesh Based on the Existing Mesh

There are some ways to create a dynamic mesh from the existing mesh:

Passing a Mesh to a New Dynamic Mesh

To create a new ObjectMeshDynamic instance from this existing mesh, you should pass the existing Mesh class instance to the ObjectMeshDynamic class constructor.

Usage Example

The following example shows how to create a new dynamic mesh from the existing Mesh class instance. It is supposed that you already have the Mesh instance, but in this example we create a new instance of the Mesh class with the box surface.

Source code (C++)
``````// AppWorldLogic.cpp

#include <UnigineObjects.h>
#include <UnigineEditor.h>

using namespace Unigine;
using namespace Math;

int AppWorldLogic::init() {

// create the mesh with the box surface
MeshPtr mesh = Mesh::create();

// create a new ObjectMeshDynamic instance by passing mesh as an argument
ObjectMeshDynamicPtr dynamic_mesh = ObjectMeshDynamic::create(mesh);
dynamic_mesh->release();

// Assign a material and a property.
dynamic_mesh->setMaterial("mesh_base", "*");
dynamic_mesh->setProperty("surface_base", "*");

return 1;
}``````

Copy a Mesh to the Existing Dynamic Mesh

To copy the mesh from the Mesh instance to an existing dynamic mesh, you should use the setMesh() function and pass the Mesh instance as an argument to it. This function copies a given mesh into the current dynamic mesh.

Usage Example

The following example shows how to copy the mesh from the Mesh instance to the ObjectMeshDynamic instance. It is supposed that you already have the Mesh instance, but in this example we create a new instance of the Mesh class with the box surface.

Source code (C++)
``````// AppWorldLogic.cpp

#include <UnigineConsole.h>
#include <UnigineCallback.h>
#include <UnigineObjects.h>
#include <UnigineEditor.h>

using namespace Unigine;
using namespace Math;

int AppWorldLogic::init() {

// existing mesh with a box surface
MeshPtr mesh = Mesh::create();

// create a new ObjectMeshDynamic
ObjectMeshDynamicPtr dynamic_mesh = ObjectMeshDynamic::create();
dynamic_mesh->release();

// copy the existing mesh to the ObjectMeshDynamic
dynamic_mesh->setMesh(mesh);

// Assign a material and a property.
dynamic_mesh->setMaterial("mesh_base", "*");
dynamic_mesh->setProperty("surface_base", "*");

return 1;
}``````

To add some physical properties to the dynamic mesh so that it could participate in interactions between objects or external physical forces, it should have a body. You can easily assign it from the code or in the UnigineEditor.

Usage Example

The following example shows how to add the rigid body with a shape to the dynamic mesh. In the example the dynamic mesh is created from the existing mesh with the box surface.

Source code (C++)
``````// AppWorldLogic.cpp

#include <UnigineObjects.h>
#include <UnigineEditor.h>
#include <UniginePhysics.h>

using namespace Unigine;
using namespace Math;

int AppWorldLogic::init() {

// create a mesh instance with a box surface
MeshPtr mesh = Mesh::create();

// create a new dynamic mesh from the Mesh instance and add it to editor
ObjectMeshDynamicPtr dynamic_mesh = ObjectMeshDynamic::create(mesh);
dynamic_mesh->release();

// assign a material and a property to the dynamic mesh
dynamic_mesh->setWorldTransform(translate(Vec3(0.0f, 0.0f, 2.0f)));
dynamic_mesh->setMaterial("mesh_base", "*");
dynamic_mesh->setProperty("surface_base", "*");

// assign a body and a shape to the dynamic mesh
BodyRigidPtr body = BodyRigid::create(dynamic_mesh->getObject());
ShapeBoxPtr shape = ShapeBox::create(body->getBody(), vec3(0.2f));

return 1;
}``````

Intersections with Dynamic Meshes

To detect if the dynamic mesh intersects a line or bounds of the specified volume, you should use one of the following functions:

• getIntersection() of the Object class that detects the intersection of the specified object with a tracing line. For example:
Source code (C++)
``````// note: the dynamic mesh has been created in the example above

// create an ObjectIntersection instance to store intersection data
ObjectIntersectionPtr intersection = ObjectIntersection::create();
// find an intersection
if (mesh->getIntersection(vec3(0.0f), vec3(1.0f), intersection, 0))
Log::message("The dynamic mesh has been intersected by the line\n");
else Log::message("No intersections have been detected\n");``````
• getIntersection() functions of the World class that detect all the objects and nodes in the specific bounding volume or the first object intersection with the invisible tracing line. See examples of the world intersections.
• getIntersection() functions of the Physics class that detect intersections with a shape of bodies. If the object has no body, this function detects intersection with surfaces (polygons) of the object with the intersection flag. See usage example of the physics intersections here.
• getIntersection() of the Shape class detects the intersection of the specified shape with a tracing line. See the example of shape intersection here.

Saving a Dynamic Mesh to a File

To save the dynamic mesh into a file, you should copy it to the Mesh class instance. By using the save() function of the Mesh class, you can save the mesh with the specified name.

Usage Example

The following example shows how to save the dynamic mesh to the file. It is supposed that you have a dynamic mesh to save. You should pass a path as an argument to the save() function of the Mesh class. The path is relative to the data/ folder of your project.

Source code (C++)
``````// create a mesh instance
MeshPtr mesh_0 = Mesh::create();
// copy the dynamic mesh to the Mesh class instance
dynamic_mesh->getMesh(mesh_0);

// save the mesh to the data/samples/dynamic_mesh.mesh file
mesh->save("unigine_project/meshes/dynamic_mesh.mesh");``````
Last update: 26.04.2018