useBackground node

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The Use Background shader allows you to mix computer-generated objects with scanned images in a seamless way. An object with a Use Background shader does not show up in the scene; wherever that material is, you just see the background image of the scene. However, shadows can fall on the material, and if it is made shiny, it can reflect other computer-generated objects.

For example, let's say you scan in a picture of a tree, and put that on an image plane. You can then create a tube to "stand in" for this tree in the scene. Position it so that it lines up with the tree, and assign a Use Background shader to it. When you render, you will not see the tube. Rather, you will see the tree in the background image. But if a computer-generated object should cast a shadow on the tube, it will appear to be cast on the tree. And if a computer-generated object should pass behind the tube, it will sppear to be passing behind the tree in the background image.

In the table below, important attributes have their names indicated in bold in the description column.

This node is MP safe

Node name	Parents	Classification	MFn type	Compatible function sets
useBackground	dependNode	shader/surface	kUseBackground	kBase kNamedObject kDependencyNode kUseBackground

Attributes (92)

The following quick index only shows top-level attributes (too many attributes to show them all): backgroundSampler, lightDataArray (14), matteOpacity, matteOpacityMode, miAbsorbs, miAngle, miColor (3), miDeriveFromMaya, miDiffuse, miFrameBufferWriteFactor, miFrameBufferWriteFlags, miFrameBufferWriteOperation, miNormalCamera (3), miOcclusionMask, miReflectionBlur, miReflectionRays, miReflectivity, miRefractions, miRefractiveIndex, miShinyness, miSpecularColor (3), miSpreadX, miSpreadY, miTranslucence, miTranslucenceFocus, miTransparency (3), miWhiteness (3), normalCamera (3), objectId, outColor (3), outMatteOpacity (3), outTransparency (3), pointCamera (3), primitiveId, rayDepth, rayDirection (3), rayInstance, raySampler, reflectionLimit, reflectivity, shadowMask, specularColor (3)

Long name (short name) Type Default Flags

objectId (oi) addr 0

TrenderGroup*

primitiveId (pi) integer 0

triangle id

raySampler (rtr) addr 0

ray sample pointer

backgroundSampler (rtb) addr 0

background sample pointer

rayDepth (rd) short 0

current ray depth

rayInstance (ryi) integer 0

Unique ray identifier controlling the sampling distribution for volume light depth map shadows, fluid volume rendering, light fog, ray traced shadows, and motion blur.

rayDirection (rad) float3

the ray direction.

rayDirectionX (rdx) float 0.0

ray direction X value.

rayDirectionY (rdy) float 0.0

ray direction Y value.

rayDirectionZ (rdz) float 1.0

ray direction Z value.

outColor (oc) float3

output color

outColorR (ocr) float 0.0

outColor red value

outColorG (ocg) float 0.0

outColor green value

outColorB (ocb) float 0.0

outColor blue value

outTransparency (ot) float3

output Transparency

outTransparencyR (otr) float 0.0

outTransparency R value

outTransparencyG (otg) float 0.0

outTransparency G value

outTransparencyB (otb) float 0.0

outTransparency B value

pointCamera (pc) float3

surface intersection point in camera space

pointCameraX (px) float 1.0

point camera X value

pointCameraY (py) float 1.0

point camera Y value

pointCameraZ (pz) float 1.0

point camera Z value

normalCamera (n) float3

Normal Camera represents the surface normals in the camera's space. (These are used to calculate shading.)

To do Bump Mapping, connect the output of a bump node to this attribute.

normalCameraX (nx) float 1.0

normal camera x value

normalCameraY (ny) float 1.0

normal camera Y value

normalCameraZ (nz) float 1.0

normal camera Z value

lightDataArray (ltd) lightData NULL

The lighting information this node computes.

lightDirection (ld) float3

The light direction.

lightDirectionX (ldx) float 1.0

The x component of the direction.

lightDirectionY (ldy) float 1.0

The y component of the direction.

lightDirectionZ (ldz) float 1.0

The z component of the direction.

lightIntensity (li) float3

The light intensity (its a colour).

lightIntensityR (lir) float 1.0

The red component of the intensity.

lightIntensityG (lig) float 1.0

The green component of the intensity.

lightIntensityB (lib) float 1.0

The blue component of the intensity.

lightAmbient (la) bool true

The boolean that indicates if the light has an ambient component.

lightDiffuse (ldf) bool true

The boolean that indicates if the light has a diffuse component.

lightSpecular (ls) bool false

The boolean that indicates if the light has a specular component.

lightShadowFraction (lsf) float 0.5

The visibility fraction to the light. value is in [0,1]

preShadowIntensity (psi) float 1.0

Luminance of pre shadow light intensity.

lightBlindData (lbd) addr 0

The light's blind data.

shadowMask (sm) float 1.0

shadow attenuation. If less than 1.0, it makes the shadows appear dimmer. At a value of 0, the shadows are not visible.

reflectionLimit (fll) short 2

reflected ray depth limit

specularColor (sc) float3

Specular Color is the color of the specular reflections (also called 'hot spots') on the material. The final color of a specular reflection is a combination of the Specular Color and the color of the light.

By making the Specular Color brighter or dimmer, you can control the brightness of the specular reflections on an object.

Tip: To make a material look more plastic, use white for the specular color. To make a material look more metallic, make the specular color similar to the surface color.

specularColorR (sr) float 0.5

specular color red value

specularColorG (sg) float 0.5

specular color green value

specularColorB (sb) float 0.5

specular color blue value

reflectivity (rfl) float 0.5

Reflectivity is used to make an object reflect light like a mirror. Set this to 0 is you don't want your material to reflect at all. Increase the value to make brighter reflections. Note that brighter reflections hide more of the base surface color.

This attribute is only meaningful if there is a reflection map, or if you are doing Ray Tracing.

Here are some useful values for Reflectivity:

Note: If you are doing Ray Tracing, and you want other objects in the scene to be seen in reflections, then you must turn on the Visible In Reflections attribute of those objects.

matteOpacityMode (mom) enum 2

Matte Opacity Mode controls how the system will use the Matte Opacity attribute (below). When you are rendering with a matte (i.e. an alpha channel, or mask), these two attributes are used to control how this material will show up in the matte. This is useful if you will be compositing your rendered images later on.

There are three settings, used for different purposes:

Opacity Gain

Solid Matte: This is like Opacity Gain, except that the normally-calculated matte values are ignored in favor of the Matte Opacity setting. The entire matte for the object is set to the value of the Matte Opacity attribute. If there are transparent areas on the object, their transparency is ignored in the matte. Use this setting to composite an object with transparent parts, when you don't want the background to show through them.

matteOpacity (mog) float 1.0

Matte Opacity is used (along with Matte Opactiy Mode) to affect how the matte (i.e. alpha channel or mask) for this material will be calculated. See Matte Opacity Mode above for full details.

outMatteOpacity (omo) float3

output Matte Opacity

outMatteOpacityR (omor) float 0.0

output Matte Opacity red value

outMatteOpacityG (omog) float 0.0

output Matte Opacity green value

outMatteOpacityB (omob) float 0.0

output Matte Opacity blue value

miReflectionBlur (mircb) float 0

Enable reflection blur by shooting more reflection rays. Blurry reflections require supersampling because a ray's direction is not exactly determined anymore. It may deviate (randomly) from the perfect specular direction, within the bounds specified by miReflectionBlur (in angle). A value of zero implies a perfectly specular interaction, a value of 90 a perfectly diffuse reflection or refraction. Values of 10 to 30 are a good starting point

miReflectionRays (mircr) short 1

Number of reflection rays to use for blurring. miReflectionRays specifies number of rays to use to sample the random deviation. In general more rays are required for more blurry reflections or refractions. Other sampling parameters also affect this setting: per-object samples and the Render Settings sample setting supersample in image space. If you increase any of these two settings, you may be able to reduce the number of rays without loss of quality, but significant performance gain.

miDeriveFromMaya (mifm) bool true

Derive photon shader parameters from the shading node if enabled, otherwise use explicit mental ray attributes.

miShinyness (mis) float 10

Photon shader shinyness parameter to control glossy reflection and refraction.

miAngle (mia) float 0

Photon shader angle parameter to control direction of anisotropic feature.

miSpreadX (misx) float 10

Photon shader x spread parameter to control size of anisotropic feature in x direction.

miSpreadY (misy) float 5

Photon shader spread parameter to control size of anisotropic feature in y direction.

miWhiteness (miwn) float3

Photon shader whiteness parameter.

miWhitenessR (miwnr) float 0.5

Red component.

miWhitenessG (miwng) float 0.5

Green component.

miWhitenessB (miwnb) float 0.5

Blue component.

miSpecularColor (misc) float3

Photon shader specular color parameter.

miSpecularColorR (miscr) float 0.5

Red component.

miSpecularColorG (miscg) float 0.5

Green component.

miSpecularColorB (miscb) float 0.5

Blue component.

miReflectivity (mirf) float 0.5

Photon shader reflectivity parameter.

miRefractiveIndex (miri) float 1

Photon shader index-of-refraction parameter.

miRefractions (mirc) bool true

Photon shader refractions parameter.

miAbsorbs (miab) bool true

Photon shader absorption parameter.

miDiffuse (midc) float 0.8

Photon shader diffuse parameter.

miColor (mic) float3

Photon shader base color parameter.

miColorR (micr) float 0.5

Red component.

miColorG (micg) float 0.5

Green component.

miColorB (micb) float 0.5

Blue component.

miTransparency (mit) float3

Photon shader transparency parameter.

miTransparencyR (mitr) float 0

Red component.

miTransparencyG (mitg) float 0

Green component.

miTransparencyB (mitb) float 0

Blue component.

miTranslucence (mitc) float 0

Photon shader translucency parameter.

miTranslucenceFocus (mitf) float 0.5

Photon shader translucence focus parameter.

miNormalCamera (minc) float3

Port to connect bump node for photon shader.

miNormalCameraX (mincx) float 0

X coordinate

miNormalCameraY (mincy) float 0

Y coordinate

miNormalCameraZ (mincz) float 0

Z coordinate

miOcclusionMask (mio) float 1

This attribute controls contribution from indirect diffuse illumination to the useBackground shader. The alpha value of the indirect illumination on a surface point is scaled by this attribute, and contributes to the final color and alpha. 0 means no indirect illumination on the surface, which is same as the old behaviour. If set to 1, useBackground will be affected by final gather like other material shaders, but only in grey scale.

miFrameBufferWriteOperation (mifo) enum 1

Operation to use when writing shader results to frame buffers

miFrameBufferWriteFlags (mifl) integer 0

Bitfield of flags for write operation. Currently only the first bit has any affect. It sets the shader to use the scale factor parameter when writing to frame buffers.

miFrameBufferWriteFactor (miff) float 1.0

Scale factor for frame buffer write operation