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.
par3d(..., no.readonly = FALSE, dev = cur3d(),
subscene = currentSubscene3d(dev))
rgl.par3d.names
rgl.par3d.readonly
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 in name = value
form, or a list of tagged
values. The names must come from the graphical parameters described
below.
logical; if TRUE
and there are no other
arguments, only those parameters which can be set by a
subsequent par3d()
call are returned.
integer; the RGL device.
integer; the subscene.
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.
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.
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.
OpenGL Architecture Review Board (1997). OpenGL Programming Guide. Addison-Wesley.
view3d
to set FOV
and zoom
.
open3d
for how to open a new window
with default settings for these parameters.
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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