VolumeProperty
Introduction
vtkVolumeProperty is used to represent common properties associated with volume rendering. This includes properties for determining the type of interpolation to use when sampling a volume, the color of a volume, the scalar opacity of a volume, the gradient opacity of a volume, and the shading parameters of a volume.
When the scalar opacity or the gradient opacity of a volume is not set, then the function is defined to be a constant value of 1.0. When a scalar and gradient opacity are both set simultaneously, then the opacity is defined to be the product of the scalar opacity and gradient opacity transfer functions.
Most properties can be set per "component" for volume mappers that support multiple independent components. If you are using 2 component data as LV or 4 component data as RGBV (as specified in the mapper) only the first scalar opacity and gradient opacity transfer functions will be used (and all color functions will be ignored). Omitting the index parameter on the Set/Get methods will access index = 0.
When independent components is turned on, a separate feature (useful for volume rendering labelmaps) is available. By default all components have an "opacityMode" of FRACTIONAL, which results in the usual addition of that components scalar opacity function value to the final opacity of the fragment. By setting one or more components to have a PROPORTIONAL "opacityMode" instead, the scalar opacity lookup value for those components will not be used to adjust the fragment opacity, but rather used to multiply the color of that fragment. This kind of rendering makes sense for labelmap components because the gradient of those fields is meaningless and should not be used in opacity computation. At the same time, multiplying the color value by the piecewise scalar opacity function value provides an opportunity to design piecewise constant opacity functions (step functions) that can highlight any subset of label values.
vtkColorTransferFunction is a color mapping in RGB or HSV space that uses piecewise hermite functions to allow interpolation that can be piecewise constant, piecewise linear, or somewhere in-between (a modified piecewise hermite function that squishes the function according to a sharpness parameter). The function also allows for the specification of the midpoint (the place where the function reaches the average of the two bounding nodes) as a normalize distance between nodes.
See the description of class vtkPiecewiseFunction for an explanation of midpoint and sharpness.
Usage
// create color and opacity transfer functions
const ctfun = vtkColorTransferFunction.newInstance();
ctfun.addRGBPoint(200.0, 1.0, 1.0, 1.0);
ctfun.addRGBPoint(2000.0, 0.0, 0.0, 0.0);
const ofun = vtkPiecewiseFunction.newInstance();
ofun.addPoint(200.0, 0.0);
ofun.addPoint(1200.0, 0.2);
ofun.addPoint(4000.0, 0.4);
// set them on the property
volume.getProperty().setRGBTransferFunction(0, ctfun);
volume.getProperty().setScalarOpacity(0, ofun);
volume.getProperty().setScalarOpacityUnitDistance(0, 4.5);
volume.getProperty().setInterpolationTypeToLinear();Methods
extend
Method use to decorate a given object (publicAPI+model) with vtkVolumeProperty characteristics.
| Argument | Type | Required | Description |
|---|---|---|---|
publicAPI | Yes | object on which methods will be bounds (public) | |
model | Yes | object on which data structure will be bounds (protected) | |
initialValues | IVolumePropertyInitialValues | No | (default: {}) |
getAmbient
Get the ambient lighting coefficient.
getAnisotropy
Get anisotropy of volume shadow scatter
getAverageIPScalarRange
getAverageIPScalarRangeByReference
getColorChannels
| Argument | Type | Required | Description |
|---|---|---|---|
index | Number | Yes |
getColorMixPreset
getComponentWeight
Get the scalar component weights.
| Argument | Type | Required | Description |
|---|---|---|---|
index | Number | Yes |
getDiffuse
Get the diffuse lighting coefficient.
getForceNearestInterpolation
| Argument | Type | Required | Description |
|---|---|---|---|
index | Number | Yes |
getGlobalIlluminationReach
Get the global illumination reach of volume shadow
getGradientOpacityMaximumOpacity
| Argument | Type | Required | Description |
|---|---|---|---|
index | Number | Yes |
getGradientOpacityMaximumValue
| Argument | Type | Required | Description |
|---|---|---|---|
index | Number | Yes |
getGradientOpacityMinimumOpacity
| Argument | Type | Required | Description |
|---|---|---|---|
index | Number | Yes |
getGradientOpacityMinimumValue
| Argument | Type | Required | Description |
|---|---|---|---|
index | Number | Yes |
getGrayTransferFunction
Get the currently set gray transfer function. Create one if none set.
| Argument | Type | Required | Description |
|---|---|---|---|
index | Number | Yes |
getIndependentComponents
getInterpolationType
Get the interpolation type for sampling a volume.
getInterpolationTypeAsString
Get the interpolation type for sampling a volume as a string.
getLAOKernelRadius
Get kernel radius for local ambient occlusion
getLAOKernelSize
Get kernel size for local ambient occlusion
getLabelOutlineThickness
gets the label outline thickness
getLocalAmbientOcclusion
Get local ambient occlusion flag
getMTime
Return the Modified Time which is a monotonic increasing integer global for all vtkObjects.
This allow to solve a question such as:
- Is that object created/modified after another one?
- Do I need to re-execute this filter, or not? ...
getOpacityMode
getRGBTransferFunction
Get the currently set RGB transfer function. Create one if none set.
| Argument | Type | Required | Description |
|---|---|---|---|
index | Number | Yes |
getScalarOpacity
Get the scalar opacity transfer function. Create one if none set.
| Argument | Type | Required | Description |
|---|---|---|---|
index | Number | Yes |
getScalarOpacityUnitDistance
Get the unit distance on which the scalar opacity transfer function is defined.
| Argument | Type | Required | Description |
|---|---|---|---|
index | Number | Yes |
getShade
Get the shading of a volume.
getSpecular
getSpecularPower
Get the specular power.
getUpdatedExtents
Retrieves the updated extents.
This array is cleared after every successful render.
getUseGradientOpacity
| Argument | Type | Required | Description |
|---|---|---|---|
index | Number | Yes |
getUseIndependentComponents
Get whether components should be treated independently for the given data.
| Argument | Type | Required | Description |
|---|---|---|---|
numberOfComponents | Number | Yes | The number of components in the data. |
getUseLabelOutline
getVolumetricScatteringBlending
Get the blending coefficient that interpolates between surface and volume rendering
newInstance
Method use to create a new instance of vtkVolumeProperty
setAmbient
Set the ambient lighting coefficient.
| Argument | Type | Required | Description |
|---|---|---|---|
ambient | Number | Yes | The ambient lighting coefficient. |
setAnisotropy
Set anisotropy of volume shadow scatter. This function is only effective when volumeScatterBlendCoef is greater than 0. Default value of 0.0 means light scatters uniformly in all directions. Value of -1.0 means light scatters backward, value of 1.0 means light scatters forward.
| Argument | Type | Required | Description |
|---|---|---|---|
anisotropy | Yes |
setAverageIPScalarRange
| Argument | Type | Required | Description |
|---|---|---|---|
x | Yes | ||
y | Yes |
setAverageIPScalarRangeFrom
| Argument | Type | Required | Description |
|---|---|---|---|
averageIPScalarRange | Range | Yes |
setColorMixPreset
Set the color mix code to a preset value Defaults to ColorMixPreset.DEFAULT See the test testColorMix for an example on how to use this preset.
If set to CUSTOM, a tag //VTK::CustomColorMix is made available to the user who can user shader replacements to put its own code. The given code will be used to mix the colors from each component. Each component is available as a rgba vec4: comp0, comp1... There are other useful functions or variable available. To find them, see //VTK::CustomColorMix tag in vtkVolumeFS.glsl.
setComponentWeight
Set the scalar component weights.
| Argument | Type | Required | Description |
|---|---|---|---|
index | Number | Yes | |
value | Number | Yes |
setComputeNormalFromOpacity
Set the normal computation to be dependent on the transfer function. By default, the mapper relies on the scalar gradient for computing normals at sample locations for lighting calculations. This is an approximation and can lead to inaccurate results. When enabled, this property makes the mapper compute normals based on the accumulated opacity at sample locations. This can generate a more accurate representation of edge structures in the data but adds an overhead and drops frame rate.
| Argument | Type | Required | Description |
|---|---|---|---|
computeNormalFromOpacity | Yes |
setDiffuse
Set the diffuse lighting coefficient.
| Argument | Type | Required | Description |
|---|---|---|---|
diffuse | Number | Yes | The diffuse lighting coefficient. |
setForceNearestInterpolation
Force the nearest neighbor interpolation of one or more of the components The interpolation for the rest of the volume is set using setInterpolationType
| Argument | Type | Required | Description |
|---|---|---|---|
index | Number | Yes | |
value | Boolean | Yes |
setGlobalIlluminationReach
Set the global illumination reach of volume shadow. This function is only effective when volumeScatterBlendCoef is greater than 0. Default value of 0.0 means only the neighboring voxel is considered when creating global shadow. Value of 1.0 means the shadow ray traverses through the entire volume.
| Argument | Type | Required | Description |
|---|---|---|---|
globalIlluminationReach | Yes |
setGradientOpacityMaximumOpacity
| Argument | Type | Required | Description |
|---|---|---|---|
index | Number | Yes | |
value | Number | Yes |
setGradientOpacityMaximumValue
| Argument | Type | Required | Description |
|---|---|---|---|
index | Number | Yes | |
value | Number | Yes |
setGradientOpacityMinimumOpacity
| Argument | Type | Required | Description |
|---|---|---|---|
index | Number | Yes | |
value | Number | Yes |
setGradientOpacityMinimumValue
| Argument | Type | Required | Description |
|---|---|---|---|
index | Number | Yes | |
value | Number | Yes |
setGrayTransferFunction
Set the color of a volume to a gray transfer function
| Argument | Type | Required | Description |
|---|---|---|---|
index | Number | Yes | |
func | vtkPiecewiseFunction | Yes |
setIndependentComponents
Does the data have independent components, or do some define color only? If IndependentComponents is On (the default) then each component will be independently passed through a lookup table to determine RGBA, shaded.
Some volume Mappers can handle 1 to 4 component unsigned char or unsigned short data (see each mapper header file to determine functionality). If IndependentComponents is Off, then you must have either 2 or 4 component data. For 2 component data, the first is passed through the first color transfer function and the second component is passed through the first scalar opacity (and gradient opacity) transfer function. Normals will be generated off of the second component. When using gradient based opacity modulation, the gradients are computed off of the second component. For 4 component data, the first three will directly represent RGB (no lookup table). The fourth component will be passed through the first scalar opacity transfer function for opacity and first gradient opacity transfer function for gradient based opacity modulation. Normals will be generated from the fourth component. When using gradient based opacity modulation, the gradients are computed off of the fourth component.
| Argument | Type | Required | Description |
|---|---|---|---|
independentComponents | Boolean | Yes |
setInterpolationType
Set the interpolation type for sampling a volume.
| Argument | Type | Required | Description |
|---|---|---|---|
interpolationType | InterpolationType | Yes |
setInterpolationTypeToFastLinear
Set interpolation type to FAST_LINEAR
setInterpolationTypeToLinear
Set interpolation type to LINEAR
setInterpolationTypeToNearest
Set interpolation type to NEAREST
setLAOKernelRadius
Set kernel radius for local ambient occlusion. It specifies the number of samples that are considered on each random ray. Value must be greater than or equal to 1.
| Argument | Type | Required | Description |
|---|---|---|---|
LAOKernelRadius | Yes |
setLAOKernelSize
Set kernel size for local ambient occlusion. It specifies the number of rays that are randomly sampled in the hemisphere. Value is clipped between 1 and 32.
| Argument | Type | Required | Description |
|---|---|---|---|
LAOKernelSize | Yes |
setLabelOutlineThickness
It will set the label outline thickness for the labelmaps. It can accept a single number or an array of numbers. If a single number is provided, it will be used for all the segments. If an array is provided, it indicates the thickness for each segment index. For instance if you have a labelmap with 3 segments (0: background 1: liver 2: tumor), you can set the thickness to [2,4] to have a thicker outline for the tumor (thickness 4). It should be noted that the thickness is in pixel and also the first array value will control the default thickness for all labels when 0 or not specified.
| Argument | Type | Required | Description |
|---|---|---|---|
labelOutlineThickness | Number or Array[Number] | Yes |
setLocalAmbientOcclusion
Set whether to turn on local ambient occlusion (LAO). LAO is only effective if shading is on and volumeScatterBlendCoef is set to 0. LAO effect is added to ambient lighting, so the ambient component of the actor needs to be great than 0.
| Argument | Type | Required | Description |
|---|---|---|---|
localAmbientOcclusion | Yes |
setOpacityMode
| Argument | Type | Required | Description |
|---|---|---|---|
index | Number | Yes | |
value | Number | Yes |
setRGBTransferFunction
Set the color of a volume to an RGB transfer function
| Argument | Type | Required | Description |
|---|---|---|---|
index | Number | Yes | |
func | vtkColorTransferFunction | Yes |
setScalarOpacity
Set the scalar opacity of a volume to a transfer function
| Argument | Type | Required | Description |
|---|---|---|---|
index | Number | Yes | |
func | vtkPiecewiseFunction | Yes |
setScalarOpacityUnitDistance
Set the unit distance on which the scalar opacity transfer function is defined.
| Argument | Type | Required | Description |
|---|---|---|---|
index | Number | Yes | |
value | Number | Yes |
setShade
Set the shading of a volume.
If shading is turned off, then the mapper for the volume will not perform shading calculations. If shading is turned on, the mapper may perform shading calculations - in some cases shading does not apply (for example, in a maximum intensity projection) and therefore shading will not be performed even if this flag is on. For a compositing type of mapper, turning shading off is generally the same as setting ambient=1, diffuse=0, specular=0. Shading can be independently turned on/off per component.
| Argument | Type | Required | Description |
|---|---|---|---|
shade | Boolean | Yes |
setSpecular
| Argument | Type | Required | Description |
|---|---|---|---|
specular | Number | Yes |
setSpecularPower
Set the specular power.
| Argument | Type | Required | Description |
|---|---|---|---|
specularPower | Number | Yes |
setUpdatedExtents
Informs the mapper to only update the specified extents at the next render.
If there are zero extents, the mapper updates the entire volume texture. Otherwise, the mapper will only update the texture by the specified extents during the next render call.
This array is cleared after a successful render.
| Argument | Type | Required | Description |
|---|---|---|---|
extents | Yes |
setUseGradientOpacity
| Argument | Type | Required | Description |
|---|---|---|---|
index | Number | Yes | |
value | Boolean | Yes |
setUseLabelOutline
| Argument | Type | Required | Description |
|---|---|---|---|
useLabelOutline | Boolean | Yes |
setVolumetricScatteringBlending
Set the blending coefficient that determines the interpolation between surface and volume rendering. Default value of 0.0 means shadow effect is computed with phong model. Value of 1.0 means shadow is created by volume occlusion.
| Argument | Type | Required | Description |
|---|---|---|---|
volumeScatterBlendCoef | Yes |