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.
par3d(…, no.readonly = FALSE, dev = rgl.cur(),
subscene = currentSubscene3d(dev))open3d(…, params = getr3dDefaults(),
useNULL = rgl.useNULL())
getr3dDefaults()
r3dDefaults
arguments in tag = value form, or a list of tagged
values. The tags 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.
a list of graphical parameters
whether to use the null graphics device
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.
The r3dDefaults variable is a list containing default
settings. The getr3dDefaults function searches the user's
global environment for r3dDefaults and returns the
one in the rgl namespace if it was not found there.
The components of the list may include any settable par3d
parameter, or "material", which should include a list
of default material3d properties, or "bg",
which is a
list of defaults to pass to the bg3d function.
R.O. indicates read-only arguments: These may only be used in queries, i.e., they do not set anything.
activeSubsceneR.O. integer. Used
with rgl.setMouseCallbacks: during a
callback, indicates the id of the subscene that was clicked.
antialiasR.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.
cexreal. The default size for text.
familycharacter. The default device independent family name; see text3d.
Applies to the whole device.
fontinteger. The default font number (from 1 to 5; see text3d).
Applies to the whole device.
useFreeTypelogical. Should FreeType fonts be used? Applies to the whole device.
fontnameR.O.; the system-dependent name of the current font. Applies to the whole device.
FOVreal. 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.
ignoreExtentlogical. Set to TRUE so that subsequently plotted objects
will be ignored in calculating the bounding box of the scene. Applies to the
whole device.
maxClipPlanesR.O.; an integer giving the maximum number of clip planes that can be defined in the current system. Applies to the whole device.
modelMatrixR.O.; a 4 by 4 matrix describing the position of the user data. See the Note below.
listenersinteger. 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.)
mouseModecharacter. A vector of 4 strings describing
what the 3 mouse buttons and the mouse wheel do.
Partial matching is used. Possible values for the first 3 entries of mouseMode (corresponding
to the mouse buttons) 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.
"none"No action.
"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”.
"user"Used when a user handler is set by
rgl.setWheelCallback.
observerR.O.; the position of the observer relative to
the model. Set by observer3d. See the Note below.
projMatrixR.O.; a 4 by 4 matrix describing the current projection of the scene.
scalereal. A vector of 3 values indicating the amount by which to
rescale each axis before display. Set by aspect3d.
skipRedrawwhether 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.
userMatrixa 4 by 4 matrix describing user actions to display the scene.
userProjectiona 4 by 4 matrix describing changes to the projection.
viewportreal. 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.
zoomreal. A positive value indicating the current magnification of the scene.
bboxR.O.; real. A vector of six values indicating the current values of the bounding box of the scene (xmin, xmax, ymin, ymax, zmin, zmax)
windowRectinteger. 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 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.
If s has the "model" set to "modify", a similar collection of
matrices using parameters from the parent subscene.
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.
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.
OpenGL Architecture Review Board (1997). OpenGL Programming Guide. Addison-Wesley.
rgl.viewpoint to set FOV and zoom.
rgl.useNULL for default usage of null device.
# NOT RUN {
r3dDefaults
open3d()
shade3d(cube3d(color = rep(rainbow(6), rep(4, 6))))
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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