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Just like the real world, in Unity
we use lights to illuminate our scenes.
Without lights nothing would be visible
to the cameras in our scene.
Broadly there are two types of lighting in Unity
dynamic and baked lighting.
Dynamic lighting is calculated in
real time while our game is running.
This can be achieved simply by adding lights to our scene.
Baked lighting is calculated offline
and saved to a texture.
These lighting texture maps are then applied
to the baked objects in the scene
for improved performance.
For more information on baked and dynamic
lighting see the lesson linked below.
To light our scene we use the Light component.
Like all components in Unity
the light component is attached to a game object.
We can move the light within our scene
using the game objects transform.
The light component has four different types of lights.
The Point Light, the Directional Light,
the Spot Light and for baked
lighting only, the Area Light.
Each of these types behave completely differently
in the way they effect the look of our game.
The point light behaves like a bare light bulb.
The point light illuminates objects in the scene
based on the light's position in the scene.
Rotation has no influence on the light
as this light shines equally
in all directions.
The directional light behaves like the sun.
Directional lights effect all the objects in the scene
lighting them based on the direction of the light
set by the game object's rotation.
Position in the scene is irrelevant.
Spot lights behave like a flashlight
or headlamps on a car.
They point in a direction based
on their transform's rotation
and illuminate all objects within a cone.
So spot lights respond to both
rotation and position.
Area lights only work when baking a light map.
Area lights shine in all directions to
one side of a rectangular plane.
In addition to these four main types of lights
there are two other items that can
influence the lighting in the scene.
Ambient light and emissive materials.
Ambient light controls global
non directional lighting in the scene.
Ambient light works with both dynamic
and baked lighting.
For complete control set the
ambient light to black
and use only the lighting in the scene.
Emissive materials are created by
setting the emission property in an
appropriate self-illuminating shader.
Emissive materials work only with baked lighting.
For more information see the lessons link below.
There are several properties that let us
customise the light.
Range determines how far a light is
emitted from the centre of the game object
holding the light component.
Range only works with point and spot lights.
When we have spot selected as our light type
we also have access to the
spot angle property.
Spot angle determines the angle of the cone
used by the spot light in degrees.
Colour will control the colour of the light.
Note the scene gizmo colour will change
to match the colour property.
Intensity controls the brightness of the light
and this is independent of range.
When trying to light a scene, a combination
of all of these properties are needed
to create effective lighting.
Our lights may appear brighter as we
increase both intensity and range.
But they both have different behaviours
in the way that they light our scene.
As well as simple illumination
lights can also use a number of effects.
Shadows, flares, halos
and something called a Cookie.
A cookie acts like a virtual mask
or flag in front of the light
to create a patterned shadow.
Cookies use the alpha channel of a texture
to give the light a projected shadow pattern.
Cookies must be a 2D texture
when working with spot and directional lights.
Cookies must be a cube map
when using a point light.
This makes sense when you think about
the fact that both spot and directional lights
are shining in one direction
and point lights are shining in all directions.
When using directional lights
there is an option to change the cookie's size,
scaling the pattern in the scene.
Cookies do not work with area lights.
When using baked lighting cookies only work
with spot lights and are ignored
for baked point lights and baked directional lights.
There are two types of shadows available
when casting shadows from a light.
Hard and Soft shadows.
Hard shadows are the most efficient.
Soft shadows are often more convincing.
But they're most expensive to render.
When rendering shadows there are several options.
Strength sets the value of the
darkness of the shadow.
Adjust this value until the shadow seems
correct in the scene.
Full strength, or the value of 1
is often too strong.
Resolution is simply a quality setting.
By default a light will use the value
you set in quality settings.
These values can be overridden here
on a per light basis.
For more information see the lesson on
quality settings.
Bias controls an offset value
to optimise shadow rendering
from any given light.
Bias is a setting that effects how far
from objects the shadows will start.
Values that are too low will produce artefacts,
but values that are too high will mean
that the objects appear to be hovering.
When using directional lights with soft shadows
there are two additional settings.
Softness and softness fade.
The softness is how harsh
the lines of the shadow will be
and the softness fade is a measure of
how far from the camera
the soft shadows are drawn.
For more information please see the
documentation on lights linked below.
Draw Halo will draw the default
scene halo around the light.
Halos respond to both the range
and intensity of the light.
Details for the default halo can be
set in the scene's render settings.
To override the default halo
this setting should be left off
and an individual halo component
should be used instead.
A flare is similar to a halo but
imitates a bright light source
seen through optical glass.
When a flare asset is loaded in to the flare slot
the light will render using a lens flare.
Flares only respond to the intensity of the light.
A lens flare component can be attached
directly to the game object
but then the flare property on the light
should remain empty or there will be
two flares rendered on the light.
A flare layer component must be attached
to a camera for that camera
to render a flare element.
Render Mode.
There are two different methods
of rendering dynamic lights
using vertex lighting
and using per pixel lighting.
Vertex lighting is usually the fastest
and calculates the scene's lighting
at the vertices of an objects mesh.
The lighting is then interpolated
over the surface of the mesh.
Per pixel lighting is calculated at every screen pixel
which is more expensive.
While pixel lighting is slower to render it does
allow for some effects that are not possible
with vertex lighting.
Normal mapping, light cookies and real time
shadows are only rendered for pixel lights.
Spot light shapes and specular highlights
are much better when rendered
in pixel mode as well.
Lights have a big impact on rendering speed.
The number of pixel lights can be limited
in the quality settings by
using the pixel light count property.
When you are in the forward rendering path
render mode gives explicit control
over whether a light should be rendered
as a vertex or pixel light.
Important will force the light to be
rendered per pixel and not important
will force the light to be rendered
in a faster mode using per vertex
or spherical harmonics.
For more information on render mode and
render path see the documentation link below.


Unity官方教程 (Lights - Unity Official Tutorials)

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朱瑛 發佈於 2014 年 5 月 2 日
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