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

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

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

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

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

Orthographic Projection Projection lines are orthogonal to projection surface

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

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

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

Perspective Projection The view frustum of perspective projection

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

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

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 http://www.continuousphysics.com/ftp/pub/test/index.php?dir=blender/&file=physics_demos-2.42-preview34.zip

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

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

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

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

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

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

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

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

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

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

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

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.

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

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

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

Mesh editing Switch between object and edit mode Tab

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

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

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

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

Basic mesh modeling Extrude Mirror Spin SpinDup Warp

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

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

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

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.

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

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

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

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

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”

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 http://en.wikipedia.org/wiki/Subdivision_surface

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

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

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

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