Basic Object Movements

Direction Vector#

A direction vector is an 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.

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. The direction vector is visualized for clarity.

Source code (C#)

// AppWorldLogic.cs

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;

using Unigine;

#if UNIGINE_DOUBLE
    using Vec3 = Unigine.dvec3;
    using Vec4 = Unigine.dvec4;
    using Mat4 = Unigine.dmat4;
#else
    using Vec3 = Unigine.vec3;
    using Vec4 = Unigine.vec4;
    using Mat4 = Unigine.mat4;
#endif


namespace UnigineApp
{
	class AppWorldLogic : WorldLogic
	{
		// define the ObjectMeshStatic instance
		// so that it will be deleted with the AppWorldLogic instance
		ObjectMeshStatic mesh;
		
		PlayerSpectator player;
		
		// define the movement speed
        float movement_speed = 5.0f;

		public AppWorldLogic()
		{
		}

        public override bool Init()
        {
            
            // enable visualizer
			Visualizer.Enabled = true;

			// create a camera and add it to the world
			player = new PlayerSpectator();

			// set the camera position and direction so that it is pointed at the object
			player.Position = new Vec3(4.0f, -3.401f, 1.5f);
			player.SetDirection(new vec3(0.0f, 1.0f, -0.4f),player.Up);
			Game.Player = player;

			// create a mesh by adding a box surface to it
			Mesh mesh_0 = new Mesh();
			mesh_0.AddBoxSurface("box_surface", new vec3(1.0f));
			// create the ObjectMeshStatic by using the new mesh
			mesh = new ObjectMeshStatic(mesh_0);

			// set the mesh position and material
			mesh.Position = new Vec3(4.0f,0.0f,1.0f);
			mesh.SetMaterial("mesh_base", "*");

			// check if the key is pressed and update the state of the specified control
			// you can use both 'p' or ASCII code (112)
			ControlsApp.SetStateKey(Controls.STATE_AUX_0, 'p');

            return true;
        }

		// start of the main loop
		public override bool Update()
		{
			// get the frame duration
			float ifps = Engine.ifps;

			// get the current world transformation matrix of the mesh
			Mat4 transform = mesh.WorldTransform;

			// get the direction vector of the mesh from the second column of the transformation matrix
			Vec3 direction = transform.GetColumn3(1);
			
			// render the direction vector for visual clarity
			Visualizer.RenderDirection(mesh.WorldPosition, new vec3(direction), new vec4(1.0f, 0.0f, 0.0f, 1.0f), 0.1f, 0);

			// check if the control key is pressed
			if (ControlsApp.GetState(Controls.STATE_AUX_0) == 1) {

				// calculate the delta of movement
				Vec3 delta_movement = direction * movement_speed * ifps;

				// set a new position to the mesh
				mesh.WorldPosition = mesh.WorldPosition + delta_movement;
			}
			
			return true;
		}
	}
}

Another Way of Setting Mesh Position

The new position can be also set by setting the WorldTransform variable. The following examples contain the code from the Update() function of the AppWorldLogic class. The part of controls initialization is the same for this method, the difference is in the Update() function only.

Source code (C#)

// check if the control key is pressed
if (ControlsApp.GetState(Controls.STATE_AUX_0) == 1) {

	// calculate the delta of movement
	Vec3 delta_movement = direction * movement_speed * ifps;

	// set a new position to the mesh
	mesh.WorldTransform = MathLib.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:

Source code (C#)

// check if the control key is pressed.
if (ControlsApp.GetState(Controls.STATE_AUX_0) == 1) {

	// calculate the delta of movement
	Vec3 delta_movement = direction * movement_speed * ifps;

	// set a new position
	// here, you can also use transform.setColumn3(3, transform.getColumn3(3) + delta_movement);
	transform.SetColumn(3, transform.GetColumn(3) + new Vec4(delta_movement, 1.0f));

	// set a new world transform matrix to the mesh
	mesh.WorldTransform = transform;
}

Rotation#

This section contains implementation of the mesh rotation.

You can rotate the mesh in two ways, by changing the transformation matrix represented by the WorldTransform variable (recommended way) or via the SetWorldRotation() function. The following example uses the second one:

Source code (C#)

// AppWorldLogic.cs

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;

using Unigine;

#if UNIGINE_DOUBLE
    using Vec3 = Unigine.dvec3;
    using Vec4 = Unigine.dvec4;
    using Mat4 = Unigine.dmat4;
#else
    using Vec3 = Unigine.vec3;
    using Vec4 = Unigine.vec4;
    using Mat4 = Unigine.mat4;
#endif


namespace UnigineApp
{
	class AppWorldLogic : WorldLogic
	{
		
        // define the ObjectMeshStatic instance
        // so that it will be deleted with the AppWorldLogic instance
        ObjectMeshStatic mesh;
		
		PlayerSpectator player;
        // define the rotation speed
        float rotation_speed = 30.0f;

		public AppWorldLogic()
		{
		}
		
        public override bool Init()
        {
            
           // enable visualizer
	        Visualizer.Enabled = true;

	        // create a camera and add it to the world
	        player = new PlayerSpectator();

	        // set the camera position and direction so that it is pointed at the object
	        player.Position = new Vec3(4.0f, -3.401f, 1.5f);
	        player.SetDirection(new vec3(0.0f, 1.0f, -0.4f),player.Up);
	        Game.Player = player;

	        // create a mesh by adding a box surface to it
	        Mesh mesh_0 = new Mesh();
	        mesh_0.AddBoxSurface("box_surface", new vec3(1.0f));
	        // create the ObjectMeshStatic by using the new mesh
	        mesh = new ObjectMeshStatic(mesh_0);

	        // set the mesh position and material
	        mesh.Position = new Vec3(4.0f,0.0f,1.0f);
	        mesh.SetMaterial("mesh_base", "*");
	
	        // check if the key is pressed and update the state of the specified control
	        // you can use both 'o' or ASCII code (111)
	        ControlsApp.SetStateKey(Controls.STATE_AUX_1, 'o');
			
            return true;
        }

		// start of the main loop
		public override bool Update()
		{
			// get the frame duration
	        float ifps = Engine.ifps;

	        // check if the control key is pressed
	        if (ControlsApp.GetState(Controls.STATE_AUX_1) == 1) {

		        // set the node rotation along the Z axis assuming node's scale equal to 1
		        mesh.SetWorldRotation(mesh.GetWorldRotation() * new quat(MathLib.RotateZ(rotation_speed * ifps)), 1);
	        }
			return true;
		}
	}
}

In the example above, the node is rotated to the left by pressing the "o" keyboard key.

Notice

It is recommended to set the second argument of the SetWorldRotation() function to 1 for all non-scaled nodes to improve performance and accuracy.
Scaling of nodes should be avoided whenever possible, as it requires addidional calculations and may lead to error accumulation.

To rotate the object by via the WorldTransform variable, you should replace the line with the SetWorldRotation() function in the example above with the following one:

Source code (C#)

mesh.WorldTransform = mesh.WorldTransform * new Mat4(MathLib.RotateZ(rotation_speed * ifps));

This way is preferred, especially in case of complex transformations, as it allows to compose transformation matrix and set it only once.

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 it. You can rotate the mesh by using the "o", "[" keyboard keys and move forward by using the "p" key.

Source code (C#)

// AppWorldLogic.cs

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;

using Unigine;

#if UNIGINE_DOUBLE
    using Vec3 = Unigine.dvec3;
    using Vec4 = Unigine.dvec4;
    using Mat4 = Unigine.dmat4;
#else
    using Vec3 = Unigine.vec3;
    using Vec4 = Unigine.vec4;
    using Mat4 = Unigine.mat4;
#endif

namespace UnigineApp
{
	class AppWorldLogic : WorldLogic
	{
        // define the ObjectMeshStatic instance
        // so that it will be deleted with the AppWorldLogic instance
        ObjectMeshStatic mesh;
		
		PlayerSpectator player;
        // define the movement and rotation speed
        float movement_speed = 5.0f;
        float rotation_speed = 30.0f;

		public AppWorldLogic()
		{
		}
		
        public override bool Init()
        {
            
           // enable visualizer
	        Visualizer.Enabled = true;

	        // create a camera and add it to the world
	        player = new PlayerSpectator();

	        // set the camera position and direction so that it is pointed at the object
	        player.Position = new Vec3(4.0f, -3.401f, 1.5f);
	        player.SetDirection(new vec3(0.0f, 1.0f, -0.4f),player.Up;
	        Game.Player = player;

	        // create a mesh by adding a box surface to it
	        Mesh mesh_0 = new Mesh();
	        mesh_0.AddBoxSurface("box_surface", new vec3(1.0f));
	        // create the ObjectMeshStatic by using the new mesh
	        mesh = new ObjectMeshStatic(mesh_0);

	        // set the mesh position and material
	        mesh.Position = new Vec3(4.0f,0.0f,1.0f);
	        mesh.SetMaterial("mesh_base", "*");
	
	        // check if the key is pressed and update the state of the specified control
	        // you can use both 'p', 'o', '[' or ASCII codes (112, 111, 113)
	        ControlsApp.SetStateKey(Controls.STATE_AUX_0, 'p');
	        ControlsApp.SetStateKey(Controls.STATE_AUX_1, 'o');
	        ControlsApp.SetStateKey(Controls.STATE_AUX_2, '[');

            return true;
        }

		// start of the main loop
		public override bool Update()
		{
            // get the frame duration
            float ifps = Engine.ifps;

            // get the current world transform matrix of the mesh
            Mat4 transform = mesh.WorldTransform;

            // get the direction vector of the mesh from the second column of the transformation matrix
            Vec3 direction = transform.GetColumn3(1);

            // initialize rotation and movement and update flag
            Mat4 rotation = Mat4.IDENTITY;
            Vec3 delta_movement = new Vec3(0.0f);
			bool update_transform = false;

            // render the direction vector for visual clarity
            Visualizer.RenderDirection(mesh.WorldPosition, new vec3(direction), new vec4(1.0f, 0.0f, 0.0f, 1.0f));

            // check if the control key for movement is pressed
            if (ControlsApp.GetState(Controls.STATE_AUX_0) == 1)
            {
                // calculate the delta of movement
                delta_movement = direction * movement_speed * ifps;
                update_transform = true;
            }

            // check if the control key for left rotation is pressed
            if (ControlsApp.GetState(Controls.STATE_AUX_1) == 1)
            {
                // set the node's left rotation along the Z axis
                rotation.SetRotateZ(rotation_speed * ifps);
                update_transform = true;
            }

            // check if the control key for right rotation is pressed
            else if (ControlsApp.GetState(Controls.STATE_AUX_2) == 1)
            {
                // set the node's right rotation along the Z axis
                rotation.SetRotateZ(-rotation_speed * ifps);
                update_transform = true;
            }
            
            // update transformation if necessary
            if (update_transform)
            {
                // combine transformations: movement + rotation
                transform = transform * rotation;
                transform.SetColumn3(3, transform.GetColumn3(3) + delta_movement);

                // set the resulting transformation
                mesh.WorldTransform = transform;
            }

			return true;
		}
	}
}

Last update: 2020-07-31

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Basic Object Movements

In This Article:

See Also#

Direction Vector#

Basic Movements#

Moving Forward#

Another Way of Setting Mesh Position

Rotation#

Combining Movements#