1. Lectures 4 and 5 Scene Management Basic Modeling Techniques
Computer Animation
Lectures 4 and 5
Scene Management
Basic Modeling Techniques

2. 3D Scenes and Camera
In computer graphics, we often use terms that are analog to theatre or photography
A virtual world is a “scene”
Objects in the scene are “actors”
There is a “camera” to specify viewing position and viewing parameters.
Viewing and projection is about how to position the camera and project the 3D scene to a 2D image

3. Viewing There should be at least one camera in the scene
You can switch cameras in the animation sequence
Camera can be animated too
The 3D scene is rendered through the viewpoint of the camera
It’s important to make sure your objects are visible through the camera, not just your eyes
Note the difference between a camera in CG and a real camera

4. Camera in computer graphics
Computer graphics uses the pinhole camera model
This results in perfectly sharp images
Real cameras use lenses with variable aperture sizes
This causes depth-of-field: out-of-focus objects appear blurry

5. Projection For each camera, there is a view volume for projection
Everything inside the view volume will be projected to the 2D plane
Everything outside the view volume will be “clipped” and ignored
Two basic projections
Orthographic projection
Perspective projection

6. Orthographic Projection
Projection lines are orthogonal to projection surface

7. Orthographic Projection
Projection plane parallel to principal face
Usually form front, top, side views
isometric (not multiview
orthographic view)
front
in CAD and architecture,
we often display three
multiviews plus isometric
side
top

8. Orthographic Projection
Preserves both distances and angles
Shapes preserved
Can be used for measurements
Building plans
Manuals
Cannot see what object really looks like because many surfaces hidden from view
Often we add the isometric view

9. Perspective Projection
Projectors converge at center of projection
Perspective projection reflects real world experience

10. Perspective Projection
The view frustum of perspective projection

11. Camera parameters in Blender
The default projection in Blender is perspective projection, you can switch to orthographic view
You can modify the following parameters in Blender
Field of view
Near plane
Far plane

12. Camera parameters in Blender
In 3D view, select camera, press F9
Demonstration

13. Blender’s game engine Can simulate rigid body dynamics
Support collision detection
Support some user interactions
Can develop a simple 3D game in this environment
See examples at

14. Scene Management Scene: Add a new scene Link object to a scene
A way to organize your objects
Scenes can share objects
Add a new scene
Four options: empty, link Object, link ObData, and Full copy
Link object to a scene
Ctrl+L

15. Outliner Outliner window helps you navigate a complex scene
If you see an empty outliner window, select “View” and then “Show Active”
LMB to select
Can toggle object level restrictions
Search by name: ctrl + F

16. Oops Diagram
Select “View” and then “Show Oops Schematic” to see the object relationship diagram

17. Content of your Blender file
To see the content of your Blender file
Shift + F4
Screen layout is stored in your Blender file
Can choose to load only the scene and not the UI layout

18. Append or Link How to merge multiple Blender files?
File  Append or Link (Shift + F1)
Can append or link object, mesh, lights, material, texture, etc.
Linking
Can only modify linked objects in the original Blender file
Useful when working as a team

19. Basic Modeling Techniques
Working with objects
Erase: x or DEL
Join: ctrl + J
Separate objects
In Edit mode, select the points or faces to be separated, then press P

20. Selection Selection Multiple selection: shift + RMB
Border select: B
Lasso Select: ctrl+LMB
Menu selection
Multiple selection: shift + RMB
Deselect: shift + RMB on the selected object
Deselect all: press A

21. Moving objects Move: Press G Axis constraint: G + (x or y or z)
Move one Blender Unit (BU) at a time: ctrl + mouse motion
Slow motion: shift + mouse motion
Move 1/10 of BU: shift + ctrl + mouse motion

22. Rotation Select and press R Axis constraint: press X or Y or Z
Rotate along local axis: R and then press X (or Y or Z) twice
Trackball rotation: R + R

23. Scaling Press S Axis constraint: press S and then X or Y or Z
In Edit mode, press Alt + S to scale selected vertices along the direction of the normals

24. Cloning
Alt+D
Or menu: Object  Duplicate Linked
Cloned objects share the same mesh, but can be individually transformed

25. Duplicate Shift + D Differences between Clone and Duplicate
Or Menu: Object  Duplicate
Differences between Clone and Duplicate
Clones share mesh
Duplicates don’t share mesh, but share materials, texture, etc.
Can see the relationships clearly in the Outliner view or Oops diagram.

26. Parenting and Grouping
Select objects and press Ctrl + P
The last object selected is the parent
Child objects will follow their parent objects
Remove parent-child relationship
(select only child objects) and then Alt + P
Grouping
Ctrl + G

27. Tracking Tracking Undo tracking Ctrl + T Alt + T
Or select the tracking object, press F7 (object), and delete the tracking constraint.

28. Undo and redo Undo: ctrl + Z Redo: shift + ctrl + Z or ctrl + Y
History: Alt + U

29. Mesh editing
Switch between object and edit mode
Tab

30. Subdivide surface
Press w, and select “Subdivide” or “Subdivide Multi”

31. Smooth a surface Press W and select smooth
Smooth out the polygon mesh
Will slightly change the shape of polygon mesh
Do not mistake it for the “Set Smooth” button under the Editing panel (F9)
“Set Smooth” means set smooth shading.
Does not change the shape of polygon mesh

32. Select vertex, line, or face
Select mode: ctrl + tab
Can also select from icons
Edge and face loop selections
Alt + RMB

33. Selections in Edit mode
Point selection: RMB
Border select: B
Circular region: B + B
Use mouse wheel to control the size of the circle
Lasso region (hand drawn region) select
Ctrl + LMB

34. Basic mesh modeling
Extrude
Mirror
Spin
SpinDup
Warp

35. Extrude In Edit mode, select one or more vertices/lines/faces, Press E
LMB to confirm
Esc to undo
One of the most useful editing techniques
Another way to add vertices to the scene
Select a vertex, then ctrl + LMB

36. Mirror In Edit mode: press M, then press X, Y, or Z
In Object mode: press ctrl + M, then press X, Y, or Z
The selected object will flip along X, Y, or Z axis to the other side of the pivot point
Don’t mistake this for Mirror Modeling

37. Spin
Useful tool for creating axially periodic structures (e.g. cup, plate, vase, etc.)
Create a profile of the object
Select all the vertices of the profile
Choose the pivot point (e.g. 3D cursor)
The spin axis will be perpendicular to the current view (e.g. top view)
In Edit mode, under Editing (F9) panel, press the Spin button

38. Spin Dup Create multiple copies of an object around a circle
In Edit mode, under Editing (F9) panel, press the Spin Dup button
Objects created by Spin Dup are considered as one entity
Separate them individually, if necessary.

39. Knife Add new edges on the faces of an object
Select the edges or faces you want to “cut”
Nothing will happen if “cut” unselected edges/faces
In Edit mode, press K
Select different types of cuts
Draw the line
Enter to confirm, Esc or RMB to cancel

40. Edge slide In Edit mode, select an edge
Press ctrl + E, then select edge slide

41. Bevel In Edit mode, press W and then select Bevel
Each edge will be split into two parallel edges and you can slide them
Purpose: to create smoothed edges

42. Vertex group and weight paint
Will talk about them when we discuss Armature based animations

43. Subsurf modifier In Edit mode, under Editing (F9) panel
A modifier is an operator that you can apply to the mesh model to change its appearance.
The change is not permanent till you press “Apply” in the object mode
Can use multiple modifiers to an object
Note the difference between the “Subdivide” button and the “Subsurf modifier”

44. Subsurf modifier Surface subdivision
Start with a low resolution model
Use subdivision to recursively generate higher and higher resolution models
Don’t over do it: more polygons means longer rendering time!
For a little more detail, check out

45. Mirror Modeling
A useful technique to model symmetrical objects (e.g. faces, etc.)
Two approaches
Use a Mirror modifier to mirror modeling on a single object
Create two clone objects and make them mirror each other

46. Mirror Modeling Mirror Modifier Select the object
Add a Mirror modifier under the Editing panel (F9)
Choose the mirror axis
The mirror modeling will happen along this axis
The mirror plane is perpendicular to this axis
Now it’s ready for mirror modeling
Press Apply button to make the changes permanent

47. Mirror Modeling The “Cloning” approach Select one object
This will be the “half” object
Press Alt + D to create a clone
They will share the same mesh model
Move the clone to the left or right
With the clone object selected, press N
In “Transform Properties”, set ScaleX ( or ScaleY, or ScaleZ) to -1.0
Now they are ready for mirror modeling
Join the two objects to make the changes permanent

48. Sculpt mode Select “Sculpt Mode” from the “Mode” menu
Under the “Sculpt” panel, can select different “Brushes”
Modify an area of the mesh with a “Brush”
E.g. can “Smooth” or “Flatten” the mesh