IDL Reference Guide: Graphics Object Classes

IDLgrVolume Properties

IDLgrVolume objects have the following properties in addition to properties inherited from any superclasses. Properties with the word "Yes" in the "Get" column of the property table can be retrieved via IDLgrVolume::GetProperty. Properties with the word "Yes" in the "Init" column of the property table can be set via IDLgrVolume::Init. Properties with the word "Yes" in the "Set" column in the property table can be set via IDLgrVolume::SetProperty.

Objects of this class have the following properties.

In addition, objects of this class inherit:

ALL

An anonymous structure containing the values of all of the properties associated with the state of this object. State information about the object includes things like color, range, tick direction, etc., but not image, vertex, or connectivity data, or user values.

ALPHA_CHANNEL

Apply to the volume only when the volume is rendered with a destination rendering quality setting of Low (0). In the case, the volume is rendered as a wireframe cube. Set this property to a floating-point value in the range [0.0, 1.0] to specify the opacity of the wireframe cube. The default value of 1.0 causes IDL to draw the wireframe cube completely opaque. If the value of this property is less than 1.0, then the pixels of the wireframe cube are blended with the pixels already on the screen, where the color of the wireframe cube is multiplied by the alpha value and the pixels already on the screen are multiplied by 1.0-alpha.

Because an object can only be blended with objects already drawn on the screen, the drawing order of the objects must be considered carefully in order to obtain the desired results.

This property has no effect on devices using indexed color mode.

AMBIENT

The color and intensity of the volume's base ambient lighting. Color is specified as a three-element vector [red, green, blue]. The default is [255, 255, 255]. AMBIENT is applicable only when LIGHTING_MODEL is set.

In a property sheet, this property appears as a color property.

BOUNDS

A six-element floating-point vector of the form [x_min, y_min, z_min, x_max, y_max, z_max], which represents the sub-volume to be rendered. .

This property is registered as a user-defined property, but it is hidden by default.

CLIP_PLANES

A 4-by-N floating-point array that specifies the coefficients of the clipping planes to be applied to this object. The four coefficients for each clipping plane are of the form [A, B, C, D], where Ax + By + Cz + D = 0. Portions of this object that fall in the half space Ax + By + Cz + D > 0 will be clipped. By default, the value of this property is a scalar (-1) indicating that no clipping planes are to be applied.

COMPOSITE_FUNCTION

An integer value or enumerated list item that determines the composite function to be used to measure the value of a pixel on the viewing plane by analyzing the voxels falling along the corresponding ray. Specify one of the following compositing functions:

dest' = src * srcalpha + 
   dest * (1 - srcalpha)  

dest' = src + dest * 
   ( 1 - srcalpha)  

DATA0

A three-dimensional array of any type of the format (d_x, d_y, d_z), which specifies a data volume. If the data volume dimensions do not match those of any pre-existing data in DATA1, DATA2, or DATA3, all existing data is removed from the object.

Specifying this property is the same as specifying the optional vol₀ argument to the IDLgrVolume::Init method.

DATA1

A three-dimensional array of any type of the format (d_x, d_y, d_z), which specifies a data volume. If the data volume dimensions do not match those of any pre-existing data in DATA0, DATA2, or DATA3, all existing data is removed from the object.

Specifying this property is the same as specifying the optional vol₁ argument to the IDLgrVolume::Init method.

DATA2

A three-dimensional array of any type of the format (d_x, d_y, d_z), which specifies a data volume. If the data volume dimensions do not match those of any pre-existing data in DATA0, DATA1, or DATA3, all existing data is removed from the object.

Specifying this property is the same as specifying the optional vol₂argument to the IDLgrVolume::Init method.

DATA3

A three-dimensional array of any type of the format (d_x, d_y, d_z), which specifies a data volume. If the data volume dimensions do not match those of any pre-existing data in DATA0, DATA1, or DATA2, all existing data is removed from the object.

Specifying this property is the same as specifying the optional vol₃ argument to the IDLgrVolume::Init method.

DEPTH_CUE

A two-element floating-point array [zbright, zdim] specifying the near and far Z planes between which depth cueing is in effect. Depth cueing is only honored when drawing to a destination object that uses the RGB color model.

Depth cueing causes an object to appear to fade into the background color of the view object with changes in depth. If the depth of an object is further than zdim (that is, if the object's location in the Z direction is farther from the origin than the value specified by zdim), the object will be painted in the background color.

Similarly, if the object is closer than the value of zbright, the object will appear in its "normal" color. Anywhere in-between, the object will be a blend of the background color and the object color. For example, if the DEPTH_CUE property is set to [-1,1], an object at the depth of 0.0 will appear as a 50% blend of the object color and the view color.

The relationship between Z_bright and Z_dim determines the result of the rendering:

You can disable depth cueing by setting z_bright = z_dim. The default is [0.0, 0.0].

This property is registered as a user-defined property, but it is hidden by default.

HIDE

A Boolean value or enumerated list item indicating whether this object should be drawn:

HINTS

An integer value or enumerated list item that specifies one of the following acceleration hints:

INTERPOLATE

A Boolean value or enumerated list item that determines whether the interpolation method.

LIGHTING_MODEL

A Boolean value that determines whether to use the current lighting model during rendering in conjunction with a local gradient evaluation.

OPACITY_TABLE0

A 256-element byte array that specifies the opacity table for DATA0. The default table is the linear ramp.

OPACITY_TABLE1

A 256-element byte array that specifies the opacity table for DATA1. The default table is the linear ramp. This table is used only when VOLUME_SELECT is set equal to 1.

PARENT

An object reference to the object that contains this object.

REGISTER_PROPERTIES

A Boolean value that determines whether to register properties available for this object. If this property is set, all properties marked in this properties section as "Registered: Yes" will be registered for display in a property sheet. This property is useful mainly when creating iTools. By default, no properties are registered.

RENDER_STEP

A three-element floating-point vector of the form [x, y, z] that specifies the stepping factor through the voxel matrix.

This property is registered as a user-defined property, but it is hidden by default.

RGB_TABLE0

A 256 x 3-element byte array that specifies the RGB color table for DATA0. The default table is the linear ramp. .

RGB_TABLE1

A 256 x 3-element byte array that specifies the RGB color table for DATA1. The default table is the linear ramp. This table is used only when VOLUME_SELECT is set equal to 1.

SHADER

An object reference to an IDLgrShader object (or an object containing IDLgrShader as a superclass). When there is suitable graphics card hardware support, the volume is rendered using the GLSL shader program (executed on the graphics card) instead of using fixed OpenGL properties when initially drawn. (If a suitable graphics card is not present, IDL ignores the shader object when the scene is drawn.) A single IDLgrShader object may be associated with additional volume objects or other graphic objects that have the SHADER property.

TWO_SIDED

A Boolean value or an enumerated list item that determines whether the lighting model uses a two-sided voxel gradient.

VALID_DATA

An integer array (one per volume, DATA0, DATA1, etc.) which have the value 1 if volume data has been loaded for that volume and 0 if that volume data is currently undefined.

VOLUME_SELECT

An integer value that selects how the volume data (DATA0, DATA1, DATA2, DATA3) is combined to form the src and srcalpha parameters described in the COMPOSITE_FUNCTION function property.

The volume data is always stored and treated as 8-bit indices into the RGB and opacity tables.

Set the RGB and/or opacity tables to linear ramps to use the volume data as direct color or opacity values. Accepted values are:

srcRed[i,j,k] = RGB_TABLE0[DATA0[i,j,k],0]  
srcGreen[i,j,k] = RGB_TABLE0[DATA0[i,j,k],1]  
srcBlue[i,j,k] = RGB_TABLE0[DATA0[i,j,k],2]  
srcAlpha[i,j,k] = OPACITY_TABLE0[DATA0[i,j,k]]  

srcRed[i,j,k] = (RGB_TABLE0[DATA0[i,j,k],0] *  
                 RGB_TABLE1[DATA1[i,j,k],0]) / 255  
srcGreen[i,j,k] = (RGB_TABLE0[DATA0[i,j,k],1] *  
                   RGB_TABLE1[DATA1[i,j,k],1]) / 255  
srcBlue[i,j,k] = (RGB_TABLE0[DATA0[i,j,k],2] *  
                  RGB_TABLE1[DATA1[i,j,k],2]) / 255  
srcAlpha[i,j,k] = (OPACITY_TABLE0[DATA0[i,j,k]] *  
                   OPACITY_TABLE1[DATA1[i,j,k]]) / 255  

srcRed[i,j,k] = RGB_TABLE0[DATA0[i,j,k],0]  
srcGreen[i,j,k] = RGB_TABLE0[DATA1[i,j,k],1]  
srcBlue[i,j,k] = RGB_TABLE0[DATA2[i,j,k],2]  
srcAlpha[i,j,k] = OPACITY_TABLE0[DATA3[i,j,k]]  

XCOORD_CONV

A floating-point vector, [s₀, s₁], of scaling factors used to convert X coordinates from data units to normalized units. The formula for the conversion is as follows:

NormalizedX = s₀ + s₁ * DataX

Recommended values are:

[(-X_min)/(X_max-X_min), 1/(X_max-X_min)]

The default is [0.0, 1.0]. IDL converts, maintains, and returns this data as double-precision floating-point.

XRANGE

A two-element double-precision floating-point vector of the form [xmin, xmax] that specifies the range of x data coordinates covered by the graphic object.

YCOORD_CONV

A floating-point vector, [s₀, s₁], of scaling factors used to convert Y coordinates from data units to normalized units. The formula for the conversion is as follows:

NormalizedY = s₀ + s₁ * DataY

Recommended values are:

[(-Y_min)/(Y_max-Y_min), 1/(Y_max-Y_min)]

The default is [0.0, 1.0]. IDL converts, maintains, and returns this data as double-precision floating-point.

YRANGE

A two-element double-precision floating-point vector of the form [ymin, ymax] that specifies the range of y data coordinates covered by the graphic object.

ZBUFFER

A Boolean value that determines whether to clip the rendering to the current Z-buffer and then update the buffer. The default is to not modify the current Z-buffer.

ZCOORD_CONV

A floating-point vector, [s₀, s₁], of scaling factors used to convert Z coordinates from data units to normalized units. The formula for the conversion is as follows:

NormalizedZ = s₀ + s₁ * DataZ

Recommended values are:

[(-Z_min)/(Z_max-Z_min), 1/(Z_max-Z_min)]

The default is [0.0, 1.0]IDL converts, maintains, and returns this data as double-precision floating-point.

ZERO_OPACITY_SKIP

A Boolean value that determines whether to skip voxels with an opacity of 0. This property can increase the output contrast of MIP (MAXIMUM_INTENSITY) projections by allowing the background to show through. If this property is set, voxels with an opacity of zero will not modify the Z-buffer. The default (not setting the property) continues to render voxels with an opacity of zero.

ZRANGE

A two-element double-precision floating-point vector of the form [zmin, zmax] that specifies the range of z data coordinates covered by the graphic object.

  IDL Online Help (March 06, 2007)