Advanced Maya Texturing and Lighting- P3 doc

By default, the light of ambient, directional, point, and spot lights never decays.. however, with point and spot lights you can force the light to lose intensity by changing the Decay r

in addition, you can animate the Color attribute by left-clicking the color swatch,

choosing a new color from the Color Chooser window, right-clicking the color swatch

or the word Color in the Attribute editor tab, and choosing Set Key from the shortcut

menu to edit the resulting animation curves, select the light and open the graph

editor (choose Window > Animation editors > graph editor)

Intensity Controls the brightness of the light you can apply a texture to this attribute

to vary the intensity across the throw of the light the texture serves as a multiplier

if intensity is set to 2 and the texture is 50 percent gray, the intensity of the light will

only be 1 when it strikes a surface

Illuminates By Default Serves as an on/off switch for the light.

Emit Diffuse and Emit Specular Determines whether the light will affect the diffuse and

specular calculations of a material during a render each attribute can be checked off

independently if only emit Specular is checked, the specular highlights will render by

themselves; however, the alpha channel will include the entire surface

Maya lights offer manipulator handles to make the positioning of the light icons easier you can activate a manipulator by selecting the light and choosing Display >

rendering > Camera/light Manipulator > manipulator name (to hide the

manipula-tor, choose it again it from the menu.) the following manipulator handles are

avail-able for all six lights:

Cycling Index Displays an upside-down Q-shaped icon that, when clicked, cycles

through all the other available manipulators (see Figure 2.2) this is perhaps the most

efficient way to use the light manipulators

Figure 2.2 A spot light’s Cycling Index manipulator

Center Of Interest Displays a Center of interest manipulator and an origin

manipula-tor (see Figure 2.3) When the Center of interest is translated, the light rotates matically to follow you can also translate the origin manipulator and thus move the body of the light

auto-Activated Pivot manipulator

Center Of Interest manipulator

Origin manipulator

Figure 2.3 A directional light’s Center Of Interest and Pivot manipulators The Pivot manipulator

handle is activated so that the Rotate tool operates around the new pivot point

Pivot Displays a handle that sets the light’s pivot point you can drag the handle’s

small circle across the light’s Center of interest line, which is automatically displayed with the pivot manipulator (see Figure 2.3) you can set the pivot in front of or behind the light to rotate the light with the new pivot point, click the small circle so that its center becomes solid yellow to return the rotation to the light’s origin, click the small circle a second time if the pivot manipulator is hidden while it is active (that

is, solid yellow at the center), the rotate tool will continue to operate around the new pivot point

By default, the light of ambient, directional, point, and spot lights never decays

that is, its intensity appears the same whether an object struck by the light is one world unit from the light or a million world units from the light however, with point and spot lights you can force the light to lose intensity by changing the Decay rate attribute to linear, Quadratic, or Cubic the Decay rate options are ordered from the mildest to the harshest (see Figure 2.4) With Quadratic, the intensity decreases proportionally with the square of the distance (intensity = 1/distance*distance), which

matches the real world When using decay, you will need to raise the intensity value of

the light For example, in Figure 2.4 each light is given an intensity value of 150 even

so, the light with the Cubic Decay rate manages to illuminate no more than 12 world

units from its origin

Using Spot Lights

Maya spot lights are named after the spotlights used on stage and in motion pictures

As opposed to their real-world counterparts, however, the light rays from a Maya

spot light are born at an infinitely small point in space the light rays quickly diverge

and follow the shape of the spot light cone Although the cone has a finite length, the

light rays continue on indefinitely the scale of the light icon does not affect the light’s

hence, flashlights, car headlights, recessed lighting, table lamps with shades, overhead lighting that “pools,” and sunlight diffusely bounced through a window are

all good candidates for spot lights (see Figure 2.5)

Figure 2.5 Real-world lighting situations that match the qualities of Maya spot lights

Spot lights are unable to accurately emulate daytime sunlight, since the spot light rays can never be parallel Additionally, if the Cone Angle of a spot light is set to

a large value, such as 120, the resulting shadows are distorted (For more information

on shadows, see Chapter 3.)

in addition to standard light manipulators, Maya spot lights include Cone Angle, penumbra, look through Barn Doors, and Decay regions manipulators you can activate these by selecting the light and choosing Display > rendering > Camera/

light Manipulator > manipulator name.

Cone Angle Creates a circular handle at the edge of the light cone that allows you to

interactively increase or decrease the Cone Angle attribute if you click-drag the small

cyan cube, the cone size will change

Penumbra Creates a circular handle at the center of the light cone that allows you to

interactively increase or decrease the penumbra attribute the penumbra represents the transition from full light intensity to no light intensity the larger the penumbra value, the softer the edge of the spot light if the penumbra is smaller than the Cone Angle, the Cone Angle establishes the outermost limit of the spot light’s illumination (see Figure 2.6) if the penumbra value is larger than the Cone Angle, the penumbra establishes the outermost limit of the spot light’s illumination

Figure 2.6 Four Cone Angle and Penumbra settings for the same spot light

Look Through Barn Doors toggles on virtual barn doors for the spot light in the real

world, barn doors are rectangular metal flaps that control the light throw of a

spot-light (see Figure 2.7)

light Manipulator > look through Barn Doors the barn doors are represented by two horizontal and two vertical cyan lines if you reduce the values of the left Barn Door, right Barn Door, top Barn Door, or Bottom Barn Door attributes in the light effects section, the barn door lines move closer to the center of the light the smaller the remaining “hole,” the smaller the rectangular light shape when the light strikes a surface if a barn door line extends past the circular edge of the light, the circular edge serves as the cutoff point for that section of the light (see Figure 2.8) you can inter-actively click and drag the barn door lines in the workspace view when panels > look through Selected is activated for the light.

Figure 2.8 (Top) Look Through Barn Door manipulators for two spot lights (Bottom) The corresponding light

shapes made by the spot lights

Decay Regions Displays circular handles that represent decay regions you can force

the light to possess specific decay regions by checking the Use Decay regions attribute

in the Decay regions section of the spot light’s Attribute editor tab three regions, labeled 1, 2, and 3, are provided each region has a Start Distance and an end Dis-tance attribute Both attributes represent a specified number of world units from the light’s origin the section between the Start Distance and end Distance represents the area where the light is active the gaps between these sections represent the areas

that receive no light hence, you can force the light to “skip” across surfaces (see

Figure 2.9) you do not have to use all three regions if the end Distance and Start

Distance values of two neighboring regions are identical, the decay between the

regions is nonexistent you can click-drag the Decay regions manipulator circles

to interactively resize the regions the Use Decay regions and Decay rate

attri-butes are compatible however, shadows are unaffected by the use of the Use Decay

regions attribute

Figure 2.9 Light “skips” across a plane when the Use Decay Regions attribute for a spot light is checked.

For a more subtle decay, you can create custom curves with a spot light’s sity attribute to do this, click the intensity Curve Create button in the light effects

inten-section of the light’s Attribute editor tab A curve node is automatically created (see

Figure 2.10) By default, the curve is given an excessive number of keyframes

never-theless, you can delete or add keys as necessary in the graph editor (choose Window >

Animation editors > graph editor) the intensity of the light is represented by the

down to up y direction of the graph the distance the light travels in world units from

its origin is represented by the left-to-right X direction of the graph the distance is

determined with the aid of a light info utility (For more information, see Chapter 7.)

By default, the curve starts at 1 and ends at 100 in the X direction, but you can scale

the curve or move keyframes if necessary

you can create similar curves for the light’s Color to do this, click the Color Curves Create button in the light effects section of the light’s Attribute editor tab in

this situation, separate curve nodes are created for the red, green, and Blue channels

once again, the default curves will have an excessive number of keyframes; these can

also be edited in the graph editor

Using Directional Lights

Directional lights provide light direction without light position that is, they are nite and constant in one direction the position and the scale of the directional light icon do not affect the light’s intensity

infi-Directional lights are ideal for emulating light that possesses one or more of the following traits:

hence, direct sunlight and moonlight are the best candidates for directional lights (see Figure 2.11)

Directional lights are ideal for set pieces that are large in world space in the same situation, a spot light would have to be placed extremely far from the subject or

have its Cone Angle increased to a very large value, which in turn would cause the

light’s shadows to become even less parallel (see Chapter 3 for a comparison of shadows)

Figure 2.11 Real-world lighting situations that match the qualities of Maya directional lights

Using Ambient Lights

Ambient lights create a soft light emanating in all directions the ambient light icon

cannot be scaled Ambient lights do not contribute to specular or bump map

calcula-tions if a scene is lit solely with ambient lights and a material has a bump map, the

bump map will not be visible

Ambient lights are ideal for emulating light that possesses one or more of the following traits:

hence, ambient lights are well suited for fill light in particular, light that bounces off walls and light that bounces off the ground are appropriate for ambient

lights (see Figure 2.12)

Figure 2.12 Real-world lighting situations that match the qualities of Maya ambient lights The camel, building, and couple

are visible in the shadow of the key light (the sun) thanks to the presence of fill light (reflected sun light)

By default, ambient lights are not truly omnidirectional the Ambient Shade attribute controls the balance between omnidirectional and directional light rays for the light the default Ambient Shade value of 0.45 mixes omnidirectional and directional rays (see Figure 2.13) if Ambient Shade is 0, the light is read with equal intensity at all points in the scene if Ambient Shade is 1, the light emanates from the current position of the light icon; in this case, the light is identical to a point light if Ambient Shade is 0, it does not matter where the light icon is placed

Ambient Shade = 0

Using Point Lights

point lights represent a light source at a fixed position light emanates in all directions

from the light icon As with a spot light, the light is generated from an infinitely small

point at the center of the icon the icon cannot be scaled

point lights are ideal for emulating light that possesses one or more of the lowing traits:

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hence, incandescent lightbulbs are the perfect candidate for point lights point lights can also emulate leDs and compact fluorescent lighting (see Figure 2.14)

Figure 2.14 Real-world lighting situations that match the qualities of Maya point lights

Using Area Lights

Area lights are physically based lights that emanate from a confined, flat area Area

lights can be scaled in two directions (X and y) Area lights have a center pointer that

indicates the direction in which the light is flowing

Area lights are ideal for emulating light that possesses one or more of the lowing traits:

hence, area lights match light filtering through a window or bouncing off a large wall Area lights can also re-create fluorescent lighting fixtures, strips

of neon light, back-lit signs, and large, dense banks of incandescent bulbs (see

Figure 2.15)

Figure 2.15 Real-world lighting situations that match the qualities of Maya area lights

Area lights do not produce parallel light rays instead, area lights create a series of rays that emanate from the light icon at sampled positions along the height and width in essence, area lights function as an array of stacked point lights (see Figure 2.16)

Figure 2.16 (Left) Area light icon (Right) A simplified representation of an area light array Red spheres represent sampled

positions that generate light rays

the intensity of an area light is affected by its intensity attribute and its relative

angle that is, if the angle between the surface normal and the light direction vector

of a single ray is large, the light intensity contribution of the ray is low if the angle

between the surface normal and the light direction vector of a single ray is small, the

light intensity contribution of that ray is high Since area lights produce a series of rays

that are sampled across the height and width of the light icon, a unique light direction

vector exists for each ray of the series

Because the light rays of an area light diverge from their origins, the edge of the area light’s throw is soft the degree of softness depends on the distance between the

light and the surface For example, the higher the light is raised above a surface, the

more diffuse the edge (the divergent rays have the opportunity to overlap to a greater

degree) Although area lights are either square or rectangular, the edge is always

rounded at the corners For a perfectly square pattern, you can use a spot light with

barn doors

Area lights, due to their nature, decay automatically nevertheless, a Decay

Rate attribute is provided to accelerate the decay process Although you can map a

texture to an area light’s Color attribute, the resulting light pattern will not be

pre-dictable; specific patterns of a bitmap will not be visible

Using Volume Lights

Volume lights possess a shape icon that dictates the extent of their light throw you

can scale and translate the shape icon to achieve different light falloffs By default, the

light’s light Shape attribute is set to Sphere you can switch the attribute to Box,

Cyl-inder, or Cone you can find the light Shape attribute in the Volume light Attributes

section of the light’s Attribute editor tab

By default, a volume light shoots light rays from the center of its shape icon in

an outward direction; in this way, the volume light is similar to a point light

how-ever, the light will never escape from or exceed the boundary of the shape icon you

can force the light rays to shoot inward from the boundary of the shape by changing

the Volume light Dir attribute to inward on the other hand, if Volume light Dir is

set to Down Axis, the light rays will be generated in parallel and will all follow the

light shape’s down axis By default, the down axis points toward negative y the axis

is indicated by the shape icon’s green arrow when Down Axis is chosen (see

Fig-ure 2.17) you can rotate the shape icon if need be

By default, the volume shape is closed however, if light Shape is set to Sphere, Cylinder, or Cone, you can reduce the Arc attribute and thus use only a

section of the light For example, if light Shape is set to Sphere, Volume light Dir

is set to outward, and Arc is set to 90, a pie-shaped wedge of light is created on

an intersecting plane

Inward arrow Down Axis arrow

Figure 2.17 Volume light with Volume Light Dir set to Outward, Inward, and Down Axis The light intersects a plane and one of two

cylinders This scene is included on the CD as volume_axis.ma

you can add additional ambient light to the volume shape by checking the emit Ambient attribute in the Color range section in this situation, ambient light is added

to all points within the volume shape

the quality of the light produced by a volume light is controlled by two ents: penumbra and Color range the penumbra gradient, which is available to Cylin-der and Cone shapes, controls the light falloff the left side of the gradient represents the intensity of the light at the volume shape’s outer edge the right side of the gradi-ent represents the intensity of the light at the shape’s center you can insert additional handles into the penumbra gradient by clicking the gradient field if a handle is pulled down to 0, the light will have zero intensity at that point Additionally, you can widen the end of the Cone shape by raising the value of the Cone end radius attribute in its default state, the Cone shape’s down axis extends from the point of the cone

gradi-the Color range gradient controls gradi-the color of gradi-the light As with gradi-the penumbra gradient, the left side corresponds to the volume shape’s outer edge you can insert addi-tional handles into the Color range gradient by clicking the gradient field the color of each handle is set by the Selected Color swatch if a handle is set to black, it effectively reduces the light’s intensity to zero at that point For example, in Figure 2.18 light Shape of a volume light is set to Box Volume light Dir is set to outward, and emit Ambient is checked three additional color handles are inserted into the Color range gradient the result is a stylized light emanating from the center of the cube

thanks to the flexibility of the light’s attributes, a volume light can function in a

simi-lar manner to an ambient, a point, or a directional light

Linking and Unlinking Lights

in Maya, there are several ways to link and unlink lights and surfaces By default, a

light is linked to all surfaces within a scene when it is created if a light is unlinked

from a surface, it no longer illuminates that surface the option is useful for lighting

complex scenes where a light may be adversely affecting some surfaces while lighting

others properly in addition, it allows different elements within a scene to have the

dedicated set of lights For instance, one character may be given one set of lights with

specific settings, while a second character is given a separate set of lights with a

com-pletely different set of settings

the quickest way to unlink a light is to select the light and surface, switch to the rendering menu set, and choose lighting/Shading > Break light links (Unlinking

affects the render View and Batch render, but is not reflected in the Smooth Shade

All workspace view.) to relink the light and surface, choose lighting/Shading > Make

light links

When linking and unlinking multiple lights and surfaces, it is often more cient to use the relationship editor For example, to unlink a light from multiple sur-

effi-faces, follow these steps:

1. Select a light Choose Window > relationship editors > light linking >

light-Centric the relationship editor window opens (see Figure 2.19)