Basic Object Movements
After adding an object to Unigine, you can control its transformations with your control devices. This article shows how to control basic object movements and combine different transformations.
See Also
- An article on Matrix Transformations.
- An article on mat4 and dmat4 Unigine data types.
- The description of Math Matrix Functions.
- The description of engine.controls functions.
Direction Vector
A direction vector is the important concept of mesh transformation. To move the node forward, you should know where is the forward direction of the mesh. When the mesh is exported from a 3D editor, it saves the information about the forward direction. And when you add the mesh to the Unigine, it will have the same orientation as it had in a 3D editor.
 |
 |
A mesh in Maya |
The same mesh in Unigine |
On pictures given above, the direction vector has positive Y-direction. To move this mesh forward, you should get the direction of the mesh by using the Y component (the second column) of the world transformation matrix of the mesh.
For example, in the City Traffic project the direction vector has positive Y-direction. To add a new car to City Traffic (to apply all the logic to the added car), it should be exported from a 3D editor with the specific direction vector.
The point is that content creators and programmers should make an arrangement about the direction vector.
Basic Movements
Moving Forward
This section contains different ways of setting the forward movement of the mesh.
In this example, we used the "p" key pressing to move the mesh forward.
// define the ObjectMeshStatic mesh and movement speed
ObjectMeshStatic mesh;
float movement_speed = 5.0f;
// initialize custom controls
void init_controls() {
// check if the key is pressed and update the state of the specified control
// you can use both 'p' or ASCII code (112)
engine.controls.setStateKey(CONTROLS_STATE_AUX_0,'p');
}
// add a mesh as a node to the editor
Node add_editor(Node node) {
engine.editor.addNode(node);
return node_remove(node);
}
/* the world script init() function
*/
int init() {
/* create a camera and add it to the world
*/
Player player = new PlayerSpectator();
player.setDirection(Vec3(0.755f,-1.0f,0.25f));
engine.game.setPlayer(player);
// add the mesh to the world and set the material
mesh = add_editor(new ObjectMeshStatic("unigine_project/meshes/statue.mesh"));
mesh.setMaterial("mesh_base", "*");
// call the init_controls() function
init_controls();
return 1;
}
/* the world script update() function
*/
int update() {
// get the frame duration
float ifps = engine.game.getIFps();
// check if the control key is pressed
if(engine.controls.getState(CONTROLS_STATE_AUX_0)) {
// get the current world transform matrix of the mesh
Mat4 transform = mesh.getWorldTransform();
// get the direction vector of the mesh
Vec3 direction = transform.m00m10m20;
// calculate the delta of movement
Vec3 delta_movement = direction * movement_speed * ifps;
// set a new position to the mesh
mesh.setWorldPosition(mesh.getWorldPosition() + delta_movement);
}
return 1;
}
Another way of getting the direction vector is by using this command:
Vec3 direction = Vec3(transform.col0);
This line is more readable, but it requires an additional casting to Vec3.
Another Way of Setting Mesh Position
The new position can be also set by using the setWorldTransform() function. The following examples contain the code from the update function of the world script. The part of controls initialization is the same for this method, the difference is in the world script's update() function.
// check if the control key is pressed
if(engine.controls.getState(CONTROLS_STATE_AUX_0)) {
// get the current world transform matrix of the mesh
Mat4 transform = mesh.getWorldTransform();
// get the direction vector of the mesh
Vec3 direction = transform.m00m10m20;
// calculate the delta of movement
Vec3 delta_movement = direction * movement_speed * ifps;
// set a new position to the mesh
mesh.setWorldTransform(translate(delta_movement) * transform);
}
Or you can change the translation column of the world transformation matrix (see the Matrix Transformations article) to move the mesh:
// check if the control key is pressed.
if(engine.controls.getState(CONTROLS_STATE_AUX_0)) {
// get the current world transform matrix of the mesh
Mat4 transform = mesh.getWorldTransform();
// get the direction vector of the mesh
Vec3 direction = transform.m00m10m20;
// calculate the delta of movement
Vec3 delta_movement = direction * movement_speed * ifps;
// set a new position
// here, you can also use transform.m03m13m23 += delta_movement;
transform.col3 += Vec4(delta_movement,1.0f);
// set a new world transform matrix to the mesh
mesh.setWorldTransform(transform);
}
Rotation
This section contains implementation of the mesh rotation.
You can rotate the mesh in two ways, by using the setWorldTransform() function or the setWorldRotation() function. The following example uses the setWorldRotation() function:
// define the ObjectMeshStatic mesh and movement speed
ObjectMeshStatic mesh;
float rotation_speed = 30.0f;
// initialize custom controls
void init_controls() {
// check if the key is pressed and update the state of the specified control
// you can use both 'o' or ASCII code (111)
engine.controls.setStateKey(CONTROLS_STATE_AUX_1,'o');
}
// add a mesh as a node to the editor
Node add_editor(Node node) {
engine.editor.addNode(node);
return node_remove(node);
}
/* the world script init() function
*/
int init() {
/* create a camera and add it to the world
*/
Player player = new PlayerSpectator();
player.setDirection(Vec3(0.755f,-1.0f,0.25f));
engine.game.setPlayer(player);
// add the mesh to the world and set the material
mesh = add_editor(new ObjectMeshStatic("unigine_project/meshes/statue.mesh"));
mesh.setMaterial("mesh_base", "*");
// call the init_controls() function
init_controls();
return 1;
}
/* the world script update() function
*/
int update() {
// get the frame duration
float ifps = engine.game.getIFps();
/* this block rotates the mesh
*/
// check if the control key is pressed.
if(engine.controls.getState(CONTROLS_STATE_AUX_1)) {
// set the node rotation along the Z axis
mesh.setWorldRotation(mesh.getWorldRotation() * quat(rotateZ(rotation_speed * ifps)));
}
return 1;
}
In the example above, the node is rotated to the left by pressing the "o" keyboard key.
To use the setWorldTransform() function, you should replace the setWorldRotation() function with the following line:
mesh.setWorldTransform(mesh.getWorldTransform() * rotateZ(rotation_speed * ifps));
Combining Movements
Combining different movement controls is not more difficult than adding only one movement control.
The following example adds a mesh to the world and allows you to control the mesh. You can rotate it by using the "o", "[" keyboard keys and move forward by using the "p" keyboard key.
// define the ObjectMeshStatic mesh and movement speed
ObjectMeshStatic mesh;
float movement_speed = 5.0f;
float rotation_speed_left = 30.0f;
float rotation_speed_right = -30.0f;
// initialize custom controls
void init_controls() {
// check if the key is pressed and update the state of the specified control
// you can use both 'p' or ASCII code (112)
engine.controls.setStateKey(CONTROLS_STATE_AUX_0,'p');
engine.controls.setStateKey(CONTROLS_STATE_AUX_1,'o');
engine.controls.setStateKey(CONTROLS_STATE_AUX_2,'[');
}
// add a mesh as a node to the editor
Node add_editor(Node node) {
engine.editor.addNode(node);
return node_remove(node);
}
/* the world script init() function
*/
int init() {
/* create a camera and add it to the world
*/
Player player = new PlayerSpectator();
player.setDirection(Vec3(0.755f,-1.0f,0.25f));
engine.game.setPlayer(player);
// add the mesh to the world and set the material
mesh = add_editor(new ObjectMeshStatic("unigine_project/meshes/statue.mesh"));
mesh.setMaterial("mesh_base", "*");
// call the init_controls() function
init_controls();
return 1;
}
/* the world script update() function
*/
int update() {
// get the frame duration
float ifps = engine.game.getIFps();
// check if the control key for moving forward is pressed
if(engine.controls.getState(CONTROLS_STATE_AUX_0)) {
// get the current world transform matrix of the mesh
Mat4 transform = mesh.getWorldTransform();
// get the direction vector of the mesh
Vec3 direction = transform.m00m10m20;
// calculate the delta of movement
Vec3 delta_movement = direction * movement_speed * ifps;
// set a new position to the mesh
mesh.setWorldPosition(mesh.getWorldPosition() + delta_movement);
}
// check if the control key for left rotation is pressed
if(engine.controls.getState(CONTROLS_STATE_AUX_1)) {
// set the node left rotation
mesh.setWorldRotation(mesh.getWorldRotation() * quat(rotateZ(rotation_speed_left * ifps)));
}
// check if the control key for right rotation is pressed
if(engine.controls.getState(CONTROLS_STATE_AUX_2)) {
// set the node right rotation
mesh.setWorldRotation(mesh.getWorldRotation() * quat(rotateZ(rotation_speed_right * ifps)));
}
return 1;
}