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02. Mouse	Tutorials	04. Node selection

03. Spheres

In this tutorial we are going to display spheres.

Estimated completion time: 10 minutes.

Table of contents

• Single sphere
• Another sphere
• Camera orientation
• Two spheres
• Summary

Single sphere

Let's display single sphere:

local nodes = main.application.nodes

local sphere = nodes:createSphere("sphere", 1)
local root = nodes:node("root")
root:addChild(sphere)

Run in ogse

Let's see into API we introduced:

• main.application.nodes instance hosts scene nodes (not necessarily visible) of scene.Node class
• main.application.nodes:createSphere() method
  • accepts name of the sphere and its radius
  • returns a new instance of scene.Node represented as a sphere

    local sphere = main.application.nodes:createSphere("sphere", 1)

• main.application.nodes:node() method
  • accepts name of the node to find among nodes hosted by main.application.nodes instance
  • returns either an instance of scene.Node that already exists, or nil otherwise

    local node = main.application.nodes:node("sphere")
    if (node)
    then
        print("Node exists")
    else
        print("Node does not exist")
    end

• scene namespace hosts scene graph management functionality
• scene.Node:addChild() method
  • accepts an instance of scene.Node to attach it as a child node

    local parent = main.application.nodes:node("parent")
    local child = main.application.nodes:node("child")
    parent:addChild(child)

Notes:

• scene node names should be unique
• root node is created by ogs and serves as the root for visible scene nodes
• only nodes that have root at the beginning of their scene graph hierarchy are visible

Another sphere

Let's display another sphere to the right of currently displayed sphere.

Add the following code:

local sphereRight = nodes:createSphere("another", 1)
root:addChild(sphereRight)
sphereRight.position = {2, 0, 0}

Run in ogse

Let's see into API we introduced:

• scene.Node.position property
  • accepts array of position components in XYZ format

    node.position = {2, 0, 0}

  • returns array of position components in XYZ format

    local pos = node.position
    print("Node position:", pos[1], pos[2], pos[3])

You probably noticed two strange things by now:

• sphereRight is actually at the left
• you only see part of the sphere

Camera orientation

These issues arise because we let camera decide its position for itself. Let's see current camera position and rotation.

Add the following code:

local camera = main.application.camera

local pos = camera.position
print("Camera position:", pos[1], pos[2], pos[3])
local rot = camera.rotation
print("Camera rotation:", rot[1], rot[2], rot[3])

Run in ogse

Let's see into API we introduced:

• main.application.camera.position property
  • accepts array of position components in XYZ format

    main.application.camera.position = {0, -30, 0}

  • returns array of position components in XYZ format

    local pos = main.application.camera.position
    print("Camera position:", pos[1], pos[2], pos[3])

• main.application.camera.rotation property
  • accepts array of rotation components in XYZ degrees

    main.application.camera.rotation = {90, 0, 0}

  • returns array of rotation components in XYZ degrees

    local rot = main.application.camera.rotation
    print("Camera rotation:", rot[1], rot[2], rot[3])

You should see something like this in the debug console:

Camera position:    0.000000    3.974028    0.000000
Camera rotation:    90.000000   0.000000    180.000000

Quite an interesting camera orientation, right?

Two spheres

You might be thinking that setting camera rotation to 0, 0, 0 would place sphereRight to the right. However, rotation alone is not enough to make scene look good. Instead, we need the following camera orientation:

• position: 0, -30, 0
• rotation: 90, 0, 0

To be honest, we came up with these values by experimenting, we don't have any logical explanation here for you. Sorry.

Now, let's display both spheres so that we can see them clearly. Here's complete code:

local nodes = main.application.nodes

local sphere = nodes:createSphere("sphere", 1)
local root = nodes:node("root")
root:addChild(sphere)

local sphereRight = nodes:createSphere("another", 1)
root:addChild(sphereRight)
sphereRight.position = {2, 0, 0}

local camera = main.application.camera

camera.position = {0, -30, 0}
camera.rotation = {90, 0, 0}

Run in ogse

Now sphereRight is finally to the right of the original sphere.

Summary

You have successfully created spherical scene nodes, positioned one of them and then oriented the camera to have a better look at the scene.

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02. Mouse	Tutorials	04. Node selection