Dynamic Meshes
The article describes operations on dynamic meshes via code by using methods of the ObjectMeshDynamic class. This class is used to procedurally create dynamic meshes and modify them in runtime. You can also load an existing mesh as a dynamic one to modify it.
See Also#
- 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:
- Add a new dynamic mesh via UnigineEditor.
- Create a new dynamic mesh by adding vertices.
- Create a new dynamic mesh from the existing 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.
Adding triangles#
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:
-
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 these functions allocate memory for polygons of the corresponding form.
- Add the corresponding number of vertices via addVertex() method.
-
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.
- Calculate tangent vectors for all vertices via updateTangents().
- Calculate a bounding box and a bounding sphere for the created mesh by calling updateBounds().
- 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) (six vertices are created) instead of an optimized addTriangleQuads(1) (four vertices are created).
Usage Example
The following example shows how to create a quad polygon by using the addTriangleQuads() function.
#include <UnigineObjects.h>
using namespace Unigine;
using namespace Math;
ObjectMeshDynamicPtr mesh;
int AppWorldLogic::init()
{
// create a dynamic mesh
mesh = ObjectMeshDynamic::create();
mesh->setWorldTransform(translate(Vec3(0.0f, 0.0f, 2.0f)));
// allocate space in a vertex buffer and create vertex indices
mesh->addTriangleQuads(1);
// add vertices and assign texture coordinates, if necessary
mesh->addVertex(vec3(-1.0f, -1.0f, 0.0f));
mesh->addTexCoord(vec4(0, 0, 0, 0));
mesh->addVertex(vec3(1.0f, -1.0f, 0.0f));
mesh->addTexCoord(vec4(1, 0, 0, 0));
mesh->addVertex(vec3(1.0f, 1.0f, 0.0f));
mesh->addTexCoord(vec4(1, 1, 0, 0));
mesh->addVertex(vec3(-1.0f, 1.0f, 0.0f));
mesh->addTexCoord(vec4(0, 1, 0, 0));
// 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.
- Allocate space for triangle vertices in an index buffer using allocateIndices().
- Allocate space for vertices in a vertex buffer using allocateVertex().
- Add the corresponding number of vertices via addVertex() method.
- Add the corresponding number of indices via addIndex() method.
- Follow steps 3-6 described above.
Usage Example
The following example shows how to create a plane by adding vertex by vertex.
#include <UnigineObjects.h>
using namespace Unigine;
using namespace Math;
ObjectMeshDynamicPtr mesh;
int AppWorldLogic::init()
{
// create a dynamic mesh
mesh = ObjectMeshDynamic::create();
mesh->setWorldTransform(translate(Vec3(0.0f, 0.0f, 2.0f)));
// allocate space in index and vertex buffers
mesh->allocateIndices(6);
mesh->allocateVertex(4);
// add vertices
mesh->addVertex(vec3(-1.0f, -1.0f, 0.0f));
mesh->addVertex(vec3(1.0f, -1.0f, 0.0f));
mesh->addVertex(vec3(1.0f, 1.0f, 0.0f));
mesh->addVertex(vec3(-1.0f, 1.0f, 0.0f));
// add indices for created vertices
mesh->addIndex(0);
mesh->addIndex(1);
mesh->addIndex(2);
mesh->addIndex(0);
mesh->addIndex(2);
mesh->addIndex(3);
// 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:
- Create a new instance of the ObjectMeshDynamic class by passing the Mesh class instance as an argument to the constructor.
- Copy the Mesh class instance to the existing ObjectMeshDynamic instance by passing the Mesh class instance as an argument to the setMesh() function.
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.
#include <UnigineObjects.h>
using namespace Unigine;
using namespace Math;
ObjectMeshDynamicPtr dynamic_mesh;
int AppWorldLogic::init()
{
// create the mesh with the box surface
MeshPtr mesh = Mesh::create();
mesh->addBoxSurface("box", vec3(1.0f));
// create a new ObjectMeshDynamic instance by passing mesh as an argument
dynamic_mesh = ObjectMeshDynamic::create(mesh);
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.
#include <UnigineObjects.h>
using namespace Unigine;
using namespace Math;
ObjectMeshDynamicPtr dynamic_mesh;
int AppWorldLogic::init()
{
// existing mesh with a box surface
MeshPtr mesh = Mesh::create();
mesh->addBoxSurface("box", vec3(2.2f));
// create a new ObjectMeshDynamic
dynamic_mesh = ObjectMeshDynamic::create();
// copy the existing mesh to the ObjectMeshDynamic
dynamic_mesh->setMesh(mesh);
return 1;
}Adding Physics to Dynamic Meshes#
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 code or in 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.
#include <UnigineObjects.h>
#include <UniginePhysics.h>
using namespace Unigine;
using namespace Math;
ObjectMeshDynamicPtr dynamic_mesh;
int AppWorldLogic::init()
{
// create a mesh instance with a box surface
MeshPtr mesh = Mesh::create();
mesh->addBoxSurface("box", vec3(0.2f));
// create a new dynamic mesh from the Mesh instance
dynamic_mesh = ObjectMeshDynamic::create(mesh);
dynamic_mesh->setWorldTransform(translate(Vec3(0.0f, 0.0f, 2.0f)));
// assign a body and a shape to the dynamic mesh
BodyRigidPtr body = BodyRigid::create(dynamic_mesh);
ShapeBoxPtr shape = ShapeBox::create(body, vec3(0.2f));
return 1;
}See Also
- The article about Physical bodies
- The article about Shapes
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.
- 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.
Read the Intersections article to know more about intersections.
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.
// 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/meshes/dynamic_mesh.mesh file
mesh_0->save("meshes/dynamic_mesh.mesh");