rgl (version 0.83-3)

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 tag = value form, or by passing them as a list of tagged values.

Usage

par3d(..., no.readonly = FALSE)
open3d(..., params=get("r3dDefaults", envir=.GlobalEnv))

Arguments

...

arguments in tag = value form, or a list of tagged values. The tags 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.

params

a list of graphical parameters

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.

concept

• FOV
• modelMatrix
• mouseMode
• projMatrix
• scale
• userMatrix
• viewport
• zoom
• bbox

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 appendingw=1, giving the vectorv = (x,y,z,1).
2. It calculates theM = 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 topar3d("scale").
   • Thepar3d("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 byMgivingu = M %*% v. Using this location and information on the normals (which have been similarly transformed), it performs lighting calculations.
4. It obtains the projection matrixP = par3d("projMatrix")and multiplies the point by it givingP %*% u = (x2, y2, z2, w2).
5. It converts back to Euclidean coordinates by dividing the first 3 coordinates byw2.
6. The new valuez2/w2represents 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, thex2andy2values are used to determine the point in the image. Thepar3d("viewport")values are used to translate from the range(-1, 1)to pixel locations, and the point is plotted.

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

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 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 of that name 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.

References

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

See Also

rgl.viewpoint to set FOV and zoom.

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")