Set or Query RGL Parameters

Description

par3d can be used to set or query graphical parameters in rgl. Parameters can be set by specifying them as arguments to par3d in tag = value form, or by passing them as a list of tagged values.

Usage

par3d(..., no.readonly = FALSE)

open3d(..., params=getr3dDefaults(), 
	    useNULL = rgl.useNULL())
	    
getr3dDefaults()

Arguments

Details

Parameters are queried by giving one or more character vectors to par3d.

par3d() (no arguments) or par3d(no.readonly=TRUE) is used to get all the graphical parameters (as a named list).

R.O. indicates read-only arguments: These may only be used in queries, i.e., they do not set anything.

open3d opens a new rgl device, and sets the parameters as requested. The r3dDefaults list returned by the getr3dDefaults function will be used as default values for parameters. As installed this sets the point of view to 'world coordinates' (i.e. x running from left to right, y from front to back, z from bottom to top), the mouseMode to (zAxis, zoom, fov), and the field of view to 30 degrees. Users may create their own variable named r3dDefaults in the global environment and it will override the installed one. If there is a bg element in the list or the arguments, it should be a list of arguments to pass to the bg3d function to set the background.

The arguments to open3d may include material, a list of material properties as in r3dDefaults, but note that high level functions such as plot3d normally use the r3dDefaults values in preference to this setting.

If useNULL is TRUE, rgl will use a “null” device. This device records objects as they are plotted, but displays nothing. It is intended for use with writeWebGL and similar functions.

Value

When parameters are set, their former values are returned in an invisible named list. Such a list can be passed as an argument to par3d to restore the parameter values. Use par3d(no.readonly = TRUE) for the full list of parameters that can be restored.

When just one parameter is queried, its value is returned directly. When two or more parameters are queried, the result is a list of values, with the list names giving the parameters.

Note the inconsistency: setting one parameter returns a list, but querying one parameter returns an object.

Parameters

antialias

R.O. in par3d, may be set in open3d. The (requested) number of hardware antialiasing planes to use (with multisample antialiasing). The OpenGL driver may not support the requested number, in which case par3d("antialias") will report what was actually set.

cex

real. The default size for text.

family

character. The default device independent family name; see text3d.

font

integer. The default font number (from 1 to 5; see text3d.

useFreeType

logical. Should FreeType fonts be used?

fontname

R.O.; the system-dependent name of the current font.

FOV

real. The field of view, from 0 to 179 degrees. This controls the degree of parallax in the perspective view. Isometric perspective corresponds to FOV=0.

ignoreExtent

logical. Set to TRUE so that subsequently plotted objects will be ignored in calculating the bounding box of the scene.

maxClipPlanes

R.O.; an integer giving the maximum number of clip planes that can be defined in the current system.

modelMatrix

R.O.; a 4 by 4 matrix describing the position of the user data.

mouseMode

character. A vector of 3 strings describing what the 3 mouse buttons do. Partial matching is used. Possible values for mouseMode are

"none"

No action for this button.

"trackball"

Mouse acts as a virtual trackball, rotating the scene.

"xAxis"

Similar to "trackball", but restricted to X axis rotation.

"yAxis"

Y axis rotation.

"zAxis"

Z axis rotation.

"polar"

Mouse rotates the scene by moving in polar coordinates.

"selecting"

Mouse is used for selection. This is not normally set by the user, but is used internally by the select3d function.

"zoom"

Mouse is used to zoom the display.

"fov"

Mouse changes the field of view of the display.

"user"

Used when a user handler is set by rgl.setMouseCallbacks.

projMatrix

R.O.; a 4 by 4 matrix describing the current projection of the scene.

scale

real. A vector of 3 values indicating the amount by which to rescale each axis before display. Set by aspect3d.

skipRedraw

whether to update the display. Set to TRUE to suspend updating while making multiple changes to the scene. See demo(hist3d) for an example.

userMatrix

a 4 by 4 matrix describing user actions to display the scene.

viewport

R.O.; real. A vector giving the dimensions of the window in pixels.

zoom

real. A positive value indicating the current magnification of the scene.

bbox

R.O.; real. A vector of six values indicating the current values of the bounding box of the scene (xmin, xmax, ymin, ymax, zmin, zmax)

windowRect

integer. A vector of four values indicating the left, top, right and bottom of the displayed window (in pixels).

Rendering

The parameters returned by par3d are sufficient to determine where rgl would render a point on the screen. Given a column vector (x,y,z), it performs the equivalent of the following operations:

1. It converts the point to homogeneous coordinates by appending w=1, giving the vector v = (x,y,z,1).

2. It calculates the M = par3d("modelMatrix") as a product from right to left of the following matrices:

   • A matrix to translate the centre of the bounding box to the origin.

   • A matrix to rescale according to par3d("scale").

   • The par3d("userMatrix") as set by the user.

   • A matrix which may be set by mouse movements.

   • A matrix to translate the origin to the centre of the viewing region.

3. It multiplies the point by M giving u = M %*% v. Using this location and information on the normals (which have been similarly transformed), it performs lighting calculations.

4. It obtains the projection matrix P = par3d("projMatrix") and multiplies the point by it giving P %*% u = (x2, y2, z2, w2).

5. It converts back to Euclidean coordinates by dividing the first 3 coordinates by w2.

6. The new value z2/w2 represents the depth into the scene of the point. Depending on what has already been plotted, this depth might be obscured, in which case nothing more is plotted.

7. If the point is not culled due to depth, the x2 and y2 values are used to determine the point in the image. The par3d("viewport") values are used to translate from the range (-1, 1) to pixel locations, and the point is plotted.

8. If hardware antialiasing is enabled, then the whole process is repeated multiple times (at least conceptually) with different locations in each pixel sampled to determine what is plotted there, and then the images are combined into what is displayed.

See ?matrices for more information on homogeneous and Euclidean coordinates.

Note that many of these calculations are done on the graphics card using single precision; you will likely see signs of rounding error if your scene requires more than 4 or 5 digit precision to distinguish values in any coordinate.

Note

The "xAxis", "yAxis" and "zAxis" mouse modes rotate relative to the coordinate system of the data, regardless of the current orientation of the scene.

When multiple parameters are set, they are set in the order given. In some cases this may lead to warnings and ignored values; for example, some font families only support cex = 1, so changing both cex and family needs to be done in the right order. For example, when using the "bitmap" family on Windows, par3d(family = "sans", cex = 2) will work, but par3d(cex = 2, family = "sans") will leave cex at 1 (with a warning that the "bitmap" family only supports that size).

References

OpenGL Architecture Review Board (1997). OpenGL Programming Guide. Addison-Wesley.

See Also

rgl.viewpoint to set FOV and zoom.

rgl.useNULL for default usage of null device.

Examples

    r3dDefaults
    open3d()
    shade3d(cube3d(color=rep(rainbow(6),rep(4,6))))
    save <- par3d(userMatrix = rotationMatrix(90*pi/180, 1,0,0))
    save
    par3d("userMatrix")    
    par3d(save)
    par3d("userMatrix")