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ModeladoModelado procedural procedural mediantemediante programaciprogramacióónn visualvisual

Gustavo Gustavo PatowPatowGeometryGeometry andand Graphics Group (GGG) Graphics Group (GGG)

UniversitatUniversitat de Girona (de Girona (UdGUdG))

Jornadas sobre estrategias de generación de entornos colaborativos virtuales

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What is/is not procedural?What is/is not procedural? This is a course about:This is a course about:

–– Procedural modelingProcedural modeling–– Procedural texturingProcedural texturing–– Procedural animationProcedural animation

““A ProcedureA Procedure”” –– a a ““blackblack--boxbox””, with well defined , with well defined input input and output, and output, for achieving a certain (small) targetfor achieving a certain (small) target..

““Procedural approachProcedural approach”” –– making things by using making things by using different different procedures procedures that follow in a clearly definite that follow in a clearly definite orderorder..

““Procedural AnimationProcedural Animation”” –– the color, sound, geometry and the color, sound, geometry and movement are manipulated procedurallymovement are manipulated procedurally

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NonNon--procedural modelingprocedural modelingPick a vertex and drag it.Pick another vertex and drag it. Pick another vertex and drag it. Pick another vertex and drag it. Pick another vertex and drag it. Pick another vertex and drag it. Pick another vertex and drag it. …

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Procedural modeling First, I need a ¼ torus. Copy and paste, and then rotate it 180

degrees, I got another side. Merge them together I got the basic shape. The basic shape is then copied to every

point on a 16x16 grid, each rotate either 0 or 90 degrees, decided randomly.

……

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Non-procedural approach

Need craftsmanship skill. Not much planning. Animator sits in front of the computer,

fine-tune here and there, until s/he feels satisfy.

Usually cannot reproduce the same result if you ask him/her to do it again.

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Procedural approach

Describes the shape/motion algorithmically. You plan a lot before you really start. Define the “procedures”, input and output you

need.– Express shape/animation as a function of parameters.

You can write down the steps clearly, reproduce it anytime, or even ask others to reproduce the result.

Need logical mind, careful planning, sometimes a little bit mathematics

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Procedural approach (cont.) Easy to change any “input parameters” to achieve

different effects.– Can easily fine-tune the results in front of your client or boss.– Can create results in a short time (because computer does much

faster than human being). Easy to add, delete, or modify the operations at any

stage.– Because every steps are recorded down by the procedures.– Compare to Maya’s “construction history”?

Suitable for:– Large amount of geometry, each has its own variation of shape

or motion (e.g. a flock of birds)– Complicated shape that cannot be created by hand, but

welldefined by algorithm/mathematics (e.g. plants and trees).– Motions that follow physics (e.g. dynamics).– Motions that follow real-world data (e.g. motion capture).

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Effort/Timeline for both approach

Non-procedural

Plan Build Modify / fine-tune

Procedural

Plan Build Modify / fine-tune

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Both are good…

I am not saying that procedural is better than non-procedural.– Procedural approach can produce something that

non-procedural approach cannot easily create, and vice verse.

They are complement of each other. A good animation may contain both elements. A good animator should know both approach,

and know when to use procedural approach, and when to use non-procedural approach.

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The tools we’ve chosen

To create procedural elements, of course, programming is the best tool.– However, most artists hate/afraid programming.

Among existing (3D) software, Houdini is one of the best to practice the “procedural” idea.– Houdini’s workflow is based on the procedural

paradigm.– Reduce the “programming effort” to minimal.– Quickly provide most common 3D elements, such as

basic shape, particles, basic rendering, etc.

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Kenneth A. Huffwww.kennethahuff.com

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Floyd Gilliswww.floydgillis.com

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William LathamEvolutionary Art and Computer

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Practical Introduction to Practical Introduction to visual procedural visual procedural

programingprograming

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The Houdini interface

Scene View

Parameters View

Node Network View

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WorkflowWorkflow Everything is created

and modified through a “network of operators (OPs)”– Each of them will take,

or generate, some “contents”.

– The contents will be processed

– Then passed to the next operator for further processing.

InitialShape

Comp

Subdiv_Facade

Insert_door

Repeat_Floors

Repeat_Windows

Insert_Window

Exception

plain_Window

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Ops CategoriesOps Categories Objects (OBJ) – networks of objects (geometry, light,

camera, etc). Geometry (SOP) – networks to construct a geometry’s

shape. Particle (POP) – networks for particle effect. Compositing (COP2) –networks for 2D compositing. Dynamic (DOP) – networks for dynamic effect. Channel (CHOP) – networks for channel’s operation.

“Channel” controls how a value changes over time. Shaders (SHOP) – networks for creating different

shaders. Output (ROP) –networks for specifying the rendering

settings. VEX Builder (VOP) – networks for the Houdini scripting

language called “VEX”.

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The Network View

we build our network of OPs here (i.e. procedures) to perform different tasks.

press TAB and choose one of the “OP” available– Need to remember the node

name…

Press ‘H’ to view all OPs

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Go “in” and “out” an OP

OBJ level

SOP level

Select anddouble-clickan OP to gointo it.

Press “u” to goback to the parentlevel.

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Information about an OP

Right-click an OP and choose “Help”. Middle-click an OP – shows the “contents”

of this OP.– Full Name: each OP has a unique name.– OP type: each OP has a type (i.e. what

procedure it does).– Points– Vertices– Primitives

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Points– most OP contains points– Points are the basic element of a 3D scene– Points contains a 3D position (x,y,z), and optionally points can

also contain color, normal, and other custom attribute (all called point attributes)

Vertices– vertices can share points, but vertices also contain their own

information– For example, if I have a cube with 6 different colored faces, then

each corner of the cube contains 3 vertices (each vertex has a different color), but these 3 vertices share the same 3D position (i.e. shared the same point)

Primitives– several points form a “primitive”– Points cannot be rendered, but primitive can– “Primitive” is a general term in Houdini, where it can be

polygons, curve surfaces (NURBS), meta-ball, etc.

Information about an OP

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The Scene View

The Scene View is a view of your scene

You can navigate this 3D view using your mouse

EDIT and VIEW mode in the Scene View: ENTER ESC

Use SPACE + key to do different viewing ops

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The Parameter View

When you select an operator in the Network View, the parameters of that operator will be shown in the Parameter View

You can modify any editable values there

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Our first Houdini model

Step 1) – Create a new Houdini file. In the OBJ level,

press TAB and create a GEOMETRY (geo)– Double-click the newly created geometry to

go into it– In the Network View, select and delete the

default FILE OP that was created for you.

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Step 2)– In the Network View, press TAB and create a

TORUS– Set the orientation of the torus to Z-axis

Display/render flag:• Turn it on to view the result in the Scene View• One and only one display flag can be turned on inside a SOP network.

Our first Houdini model

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Step 3)– Create a SPHERE OP– Increase its radius to 5– Also select “Polygon” as its “primitive type” We want the SPHERE to be made up by many

points (and those points will be passed to the next OP) A “primitive” sphere will only contain one “point” –

its center…

try middle-drag the parameter name “Radius”to see what happen

Our first Houdini model

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Step 4)– Create a COPY OP and connect the network– and see what happens!

Our first Houdini model

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Copy SOPCopy SOP

Copies the shape on the left input to every point on the right input

By default, the z-axis of the LHS shape will be oriented to match the normal of the points on the RHS– that’s why we set the orientation of the torus

to “z-axis” If available, uses the point “normal” to

orient the copies…

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Pre-view Render

Right-click and choose“View: Mantra”

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Create lights

Click the “Point Light” button on the Shelf In the OBJ level you should find a new

object (a Point Light) created

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Assigning materials To assign material to an object:

1. Create one “material” in the SHOP level.2. Assign a SHOP material to an object in the OBJ level.

Or drag it from the material palette!!

Left-drag to the model

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You can check the result by:– Go to the SHOP level: you should find a new

OP created You can fine-tune the color here.

– Go to the OBJ level, and select your model. In the Parameter Pane, select “Material” You should find the full name of the SHOP material

be put there.

Assigning materials

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A Simple Animation

Let’s setup a simple “procedural”animation

For example, let’s make the TORUS rotate according to a cyclic formula:

the sine() formula

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Select the TORUS. Right-click at its output pin, and then type TRANSFORM– A new TRANSFORM OP should be created and

connected between TORUS and COPY.

A Simple Animation

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In the Parameter Pane, type the following formula inside the Rotate-X attribute of the TRANSFORM OP:

sin($FF*5)*360

A Simple Animation

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Play the scene to see what happen You may also want to turn on the “real

time playback” to have an idea how fast the animation is in the final rendered

Real-time playback

Click this tochange the lengthof the animationif you want.

A Simple Animation

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Final Rendering

(1) Move the view

(2) Ctrl+leftclick the camera shelf button

(3) A new camera object will be created

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Final Rendering

(1) Choose a camera

(2) Lock camera (3) Navigate through the selected camera

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To render a sequence of images, you should also create an “Output driver” in the OUT level

Go to the OUT level, press TAB in the Network View and create a MANTRA OP

Tune the rendering settings in the Parameter Pane

Final Rendering

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Final RenderingChange this section if you want to render a sequence of images

Specify the image(s) name and file format. The $F4 in the file name will be replaced by the frame number, padded with 4 digits

Change this section if you want to render in a different resolution

Make sure that you are in the OUT level

Lastly, you can click the RENDER button on the upper-left corner of the Parameter Pane to start the final rendering