Lab 4

Using ygSwitch in the Scene Graph

Start yg but do not load a scene:

Open a web browser to the following location:

www.evl.uic.edu/yg

Find the link for ygObject.

What section is it in?

Create a ygObject node.

Follow the link for ygObject and compare the messages in yg with those listed in the documentation.

What messages listed in the documentation are also available for ygObject in yg?

Follow the link at the top of the ygObject page to ygGeometry.

What messages listed in the documentation for ygGeometry are also available for ygObject in yg?

Create a ygGeometry node in your scene.

Notice that ygObject and ygGeometry have the same messages except those that are specific to ygObject.

ygObject is said to be derived from ygGeometry, it inherits all of the functionality of ygGeometry and includes some of its own.

Follow the link at the top of the ygGeometry page to ygNode.

What messages listed in the documentation for ygNode are also available for ygGeometry in yg?

Create a ygNode node in your scene.

Notice that ygGeometry and ygNode have the same messages except those that are specific to ygGeometry.

ygGeometry is derived from ygNode, and ygNode is called a base node because it is not derived from any other node.

All nodes in Ygdrasil are derived from ygNode.

Delete your existing nodes and load the scene from lab 3.

Notice that you cannot see the inside walls of the house model.

1. Adjust the cull message so that you can only see the inside of the house.

2. Adjust the cull message so that you can see both the outside and inside of the house.

3. Set the wireframe message to true on both the house object and the lamp object.

4. Create a ygSwitch object as a child of the bulb frame of reference.

5. Place the spotLight and ygTransform siblings under the ygSwitch object.

Turn off any other ygLight in the scene.

Turn the ygSwitch node off by setting the off message to true.

What happened to the light and bulb?

6. Set the ygSwitch reset message to true.

What happened to the ygSwitch node?

Look at the documentation for ygSwitch.

What is the default state for the ygSwitch node?

7. Bring up the world menu and set reset to true.

What happened to the house and lamp objects?

8. Turn off the ygSwitch node again.

9. Save your lab as lab4.yg.

Open lab4.yg in the kate editor and find your ygSwitch node.

Notice that it includes the message off in between the parenthesis.

Also, notice that each ygObject node includes the file message in between the parenthesis.

The messages saved to the file are called initial messages.

They will establish the initial state of each node when the file is loaded.

And, they will establish the initial state that the world returns to when it is reset.

10. Use the replace function in the editor to replace each instance of object1 with terrain.

11. Replace each other object with its appropriate model name.

12. Copy and paste the lines of code that includes the ygSwitch and all of its children so that it appears twice.

13. Replace bulb with bulb_on in the newly added code (including the file name).

14. Save the new scene as lab4b.yg.

Reload the new scene into yg by deleting the existing scene and loading lab4b.yg.

15. Delete the spotLight node associated with the bulb model but leave the one with the bulb_on model.

What do we have to do to make the “light turn on”?

What do we have to do to make the “light turn off”?

16. Save your modified scene.