par3d can be used to set or query graphical parameters in RGL.
Parameters can be set by specifying them as arguments to
name = value form, or by passing them as a list of named
name = value form, or a list of tagged
values. The names must come from the graphical parameters described
TRUE and there are no other
arguments, only those parameters which can be set by a
par3d() call are returned.
integer; the RGL device.
integer; the subscene.
Parameters are queried by giving one or more character vectors to
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
change this. Some parameters apply to the device as a whole;
these are marked in the list below.
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.
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.
R.O. indicates read-only arguments: These may only be used in queries, i.e., they do not set anything.
R.O. integer. Used
rgl.setMouseCallbacks: during a
callback, indicates the id of the subscene that was clicked.
par3d, may be
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.
real. The default size for text.
character. The default device independent family name; see
Applies to the whole device.
integer. The default font number (from 1 to 4; see
Applies to the whole device.
logical. Should FreeType fonts be used? Applies to the whole device.
R.O.; the system-dependent name of the current font. Applies to the whole device.
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.
logical. Set to
TRUE so that subsequently plotted objects
will be ignored in calculating the bounding box of the scene. Applies to the
R.O.; an integer giving the maximum number of clip planes that can be defined in the current system. Applies to the whole device.
R.O.; a 4 by 4 matrix describing the position of the user data. See the Note below.
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.)
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
Partial matching to action names is used. Possible values for the actions are:
No action for this button.
Mouse acts as a virtual trackball, rotating the scene.
"trackball", but restricted to X axis rotation.
Y axis rotation.
Z axis rotation.
Mouse rotates the scene by moving in polar coordinates.
Mouse is used for selection. This is not normally set by the
user, but is used internally by the
Mouse is used to zoom the display.
Mouse changes the field of view of the display.
Used when a user handler is set by
Possible values for the last entry corresponding to the mouse wheel also include
Pulling on the mouse wheel increases magnification, i.e. “pulls the scene closer”.
Pulling on the mouse wheel decreases magnification, i.e. “pushes the scene away”.
Used when a user handler is set by
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,
will be added at the start of it.
R.O.; the position of the observer relative to
the model. Set by
observer3d. See the Note below.
R.O.; a 4 by 4 matrix describing the current projection of the scene.
real. A vector of 3 values indicating the amount by which to
rescale each axis before display. Set by
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.
a 4 by 4 matrix describing user actions to display the scene.
a 4 by 4 matrix describing changes to the projection.
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.
real. A positive value indicating the current magnification of the scene.
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)
integer. A vector of four values indicating the left, top, right and bottom of the displayed window (in pixels). Applies to the whole device.
"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
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
at 1 (with a warning that the
"bitmap" family only supports that size).
par3d("viewport") names the entries of the reported vector,
names are ignored when setting the viewport and entries must be specified
in the standard order.
In rgl versions 0.94.x the
modelMatrix entry had a changed meaning;
before and after that it contains a copy of the OpenGL MODELVIEW matrix.
As of version 0.100.32, when changing the
"windowRect" parameter, the
"viewport" for the root (or specified) subscene
is changed immediately. This fixes a bug where in earlier
versions it would only be changed when the window was redrawn, potentially after another command making use of the value.
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
it performs the equivalent of
the following operations:
It converts the point to homogeneous coordinates by appending
w = 1, giving
v = (x, y, z, 1).
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("userMatrix") as set by the user.
A matrix which may be set by mouse movements.
s has the
"model" set to
"modify", a similar collection of
matrices using parameters from the parent subscene.
It multiplies the point by
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
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
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.
OpenGL Architecture Review Board (1997). OpenGL Programming Guide. Addison-Wesley.
open3d() shade3d(cube3d(color = rainbow(6), meshColor = "faces")) save <- par3d(userMatrix = rotationMatrix(90*pi/180, 1, 0, 0)) highlevel() # To trigger display save #> $userMatrix #> [,1] [,2] [,3] [,4] #> [1,] 1 0.0000000 0.0000000 0 #> [2,] 0 0.3420201 0.9396926 0 #> [3,] 0 -0.9396926 0.3420201 0 #> [4,] 0 0.0000000 0.0000000 1 #> #> $.position #>  0 -70 #> par3d("userMatrix") #> [,1] [,2] [,3] [,4] #> [1,] 1 0.000000e+00 0.000000e+00 0 #> [2,] 0 6.123234e-17 -1.000000e+00 0 #> [3,] 0 1.000000e+00 6.123234e-17 0 #> [4,] 0 0.000000e+00 0.000000e+00 1 par3d(save) highlevel() par3d("userMatrix") #> [,1] [,2] [,3] [,4] #> [1,] 1 0.0000000 0.0000000 0 #> [2,] 0 0.3420201 0.9396926 0 #> [3,] 0 -0.9396926 0.3420201 0 #> [4,] 0 0.0000000 0.0000000 1