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Shadows

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Shadows & Texturing – PowerPoint PPT presentation

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Title: Shadows


1
Shadows Texturing
2
Ray Casting
  • Ray casting is a simplified version of ray
    tracing that describes the rendering process
    behind most rendering engines. The basics behind
    ray casting involves shooting rays from the eye
    or camera, one per pixel, and finding the closet
    object in the environment that intersects the
    ray. Based on material properties and lighting
    locations, a color is returned as the final color
    that particular pixel. Ray Tracing involves
    further calculation after the initial hit is
    determined.

3
Lighting Calculation
The color of each pixel in an image created with
ray casting is the combination of ambient color,
diffuse color and specular color. There are
additional lighting components for more complex
rendering algorithms. Ray tracing generally
includes additional color contributes from
reflections and refractions.
4
Lighting Calculation
Ambient Color
Diffuse Color
Specular Color
  • Ambient Color is calculated using a ambient color
    constant and an ambient light value.
  • Diffuse Color is calculated using a diffuse color
    constant and the Surface Normal and Light Vector
  • Specular Color is calculated using a specular
    color constant and the Surface, Normal, Light
    Vector, and the vector from the viewer to the
    surface point. This vector is referred to as the
    Incident Vector.

5
Shadows
  • The location and intensity of shadows is just as
    important as setting up lights. In fact a good
    deal of a lighting artists time is spent
    adjusting shadow area in order to manipulate the
    overall contrast of the image. If an image is
    rendered without cast shadows, object appear
    floating and the view looses the sense of depth.

6
Shadows
No Shadows
Soft Contact Shadows
Cast Shadows
Combined Shadows
7
Depth Map Shadows
  • Depth map shadows are the more efficient (faster)
    of the two types of shadows. Depth Map shadows
    are based on Z-depth information from the lights
    point of view.

8
Depth Map Shadows
  • When using Depth Map shadows it is important to
    adjust shadow attributes in order to get the
    desired quality of shadow without drastically
    increasing render times. In addition to light
    attributes, Depth Map Shadow are controlled by
    Depth Map Filter size which determines the
    softness of the the shadow edge and Depth Map
    Resolution with determines the amount of shadow
    detail generated. In order to save render time
    it is possible to save Depth Maps and reuse them.

9
Ray Traced Shadows
  • Ray Traced shadows are calculated by sending rays
    from the camera to surface points on geometry in
    the environment. Another ray is then sent from
    the surface point toward the light. This ray is
    used to determine if there is an object between
    the surface point and the light which will cause
    the surface point to be in shadow. Ray Traced
    shadows take longer to render that Depth Map
    Shadows, but they can produce some effects that
    are not possible with D-Map shadows.
  • Transparent Shadows
  • Colored Transparent Shadows
  • Shadow Attenuation

10
Ray Traced Shadows
  • Ray Traced shadows are controlled by an angle
    called the Light Radius which determines the
    softness of the shadow. Shadow Rays are a
    sampling setting that determines the smoothness
    of a ray traced shadow.

11
Transparent Shadows and Colored Transparent
Shadows
  • When casting shadows from objects with
    transparency like dark glass, Depth Map shadows
    do not take into account the transparent
    properties of the surface. Ray Traced shadows
    can represent the detail of a transparent surface
    including the color of the transparent material.

12
Shadow Attenuation
  • In order to create more realistic shadows for
    different lighting situations lighting artist use
    controls to adjust the hardness or softness of
    shadows. The difference between raytraced soft
    shadows and depth map soft shadows is that a
    depth map soft shadow is soft around all edges
    and ray traced soft shadows become softer or
    attenuate as the shadow edge moves farther away
    from the light source.

13
Shadow Attenuation
14
Textures
15
Textures
  • Color Map
  • Transparency Map
  • Specular Map
  • Reflectivity Map
  • Bump Map
  • Displacement Map

16
Image File Texture Maps
  • A Image File Texture Map is a digital image that
    contains surface information about a material.
    They can be used to create realistic surface
    materials if they are created from actual
    photographs. They are generally created with a
    2D paint program like Adobe Photoshop and then
    brought back into Maya as a File Texture.

17
Procedural Textures
  • Procedural Textures created using mathematical
    functions, and they can be adjusted to create
    different patterns and textures. Pattern
    generation is a large part of procedural
    texturing, this includes organic procedural
    textures like Perlin noise, and more ordered
    patterns like a checker board.

18
Shaders Shading Networks
19
Example RenderMan Surface Shader
  • surface
  • matte(
  • float Ka 1
  • float Kd 1)
  • normal Nf faceforward(N, I)
  • Oi Os
  • Ci Os Cs (Kaambient() Kddiffuse(Nf))

20
Example RenderMan Surface Shader
  • surface
  • plastic(
  • float Ka 1
  • float Kd .5
  • float Ks .5
  • float roughness .1
  • color specularcolor 1)
  • normal Nf faceforward(N, I)
  • vector V -normalize(I)
  • Oi Os
  • Ci Os (Cs (Kaambient()
    Kddiffuse(Nf))
  • specularcolor Ksspecular(Nf, V, roughness)
    )
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