par3d: 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 name = value form, or by passing them as a list of named values.

Usage

par3d(..., no.readonly = FALSE, dev = cur3d(), 
      subscene = currentSubscene3d(dev))
rgl.par3d.names
rgl.par3d.readonly

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.

Arguments

...: arguments in name = value form, or a list of tagged values. The names must come from the graphical parameters described below.
no.readonly: logical; if TRUE and there are no other arguments, only those parameters which can be set by a subsequent par3d() call are returned.
dev: integer; the RGL device.
subscene: integer; the subscene.

Parameters

The rgl.par3d.names variable contains the full list of names of par3d properties. rgl.par3d.readonly contains the list of read-only properties.

In the list below, R.O. indicates the read-only arguments: These may only be used in queries, they do not set anything.

activeSubscene

R.O. integer. Used with rgl.setMouseCallbacks: during a callback, indicates the id of the subscene that was clicked.

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. Applies to the whole device.

cex

real. The default size for text.

family

character. The default device independent family name; see text3d. Applies to the whole device.

font

integer. The default font number (from 1 to 4; see text3d). Applies to the whole device.

useFreeType

logical. Should FreeType fonts be used? Applies to the whole device.

fontname

R.O.; the system-dependent name of the current font. Applies to the whole device.

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. Applies to the whole device.

maxClipPlanes

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

modelMatrix

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

listeners

integer. A vector of subscene id values. If a subscene receives a mouse event (see mouseMode just below), the same action will be carried out on all subscenes in this list. (The subscene itself is normally listed as a listener. If it is not listed, it will not respond to its own mouse events.)

mouseMode

character. A vector of 5 strings describing mouse actions. The 5 entries are named c("none", "left", "right", "middle", "wheel"), corresponding to actions for no button, the left, right or middle button, and the mouse wheel. Partial matching to action names is used. Possible values for the actions 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.

Possible values for the last entry corresponding to the mouse wheel also include

"pull": Pulling on the mouse wheel increases magnification, i.e. “pulls the scene closer”.
"push": Pulling on the mouse wheel decreases magnification, i.e. “pushes the scene away”.
"user2": Used when a user handler is set by rgl.setWheelCallback.

A common default on Mac OSX is to convert a two finger drag on a trackpad to a mouse wheel rotation.

The first entry is for actions to take when no mouse button is pressed. Legal values are the same as for the mouse buttons.

The first entry was added after rgl version 0.106.8. For back compatibility, if the vector of actions is less than 5 entries, "none" will be added at the start of it.

observer

R.O.; the position of the observer relative to the model. Set by observer3d. See the Note below.

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. Applies to the whole device.

userMatrix

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

userProjection

a 4 by 4 matrix describing changes to the projection.

viewport

real. A vector giving the dimensions of the window in pixels. The entries are taken to be c(x, y, width, height) where c(x, y) are the coordinates in pixels of the lower left corner within the window.

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). Applies to the whole device.

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) in a subscene s, it performs the equivalent of the following operations:

It converts the point to homogeneous coordinates by appending w = 1, giving the vector v = (x, y, z, 1).
It calculates the M = par3d("modelMatrix") as a product from right to left of several 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.
- The description above applies to the usual case where there is just one subscene, or where the subscene's "model" is set to "replace". If it is set to "modify", the first step is skipped, and at the end the procedure is followed for the parent subscene. If it is set to "inherit" only the parent settings are used.
It multiplies the point by M giving u = M %*% v.
It multiplies that point by a matrix based on the observer position to translate the origin to the centre of the viewing region.
Using this location and information on the normals (which have been similarly transformed), it performs lighting calculations.
It obtains the projection matrix P = par3d("projMatrix") based on the bounding box and field of view or observer location, multiplies that by the userProjection matrix to give P. It multiplies the point by it giving P %*% u = (x2, y2, z2, w2).
It converts back to Euclidean coordinates by dividing the first 3 coordinates by w2.
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.
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.
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.

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).

By default, queries and modifications apply to the current subscene on the current device; specify dev and/or subscene to change this. Some parameters apply to the device as a whole; these are marked in the list below.

References

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

Examples

Run this code

    open3d()
    shade3d(cube3d(color = rainbow(6), meshColor = "faces"))
    save <- par3d(userMatrix = rotationMatrix(90*pi/180, 1, 0, 0))
    highlevel()  # To trigger display
    save
    par3d("userMatrix")    
    par3d(save)
    highlevel()
    par3d("userMatrix")

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