Hi
baptiste auguie wrote:
Dear all, It seems to me that grid.raster is a special case of grid.rect as far as the intended visual output is concerned. The example below illustrates how both can be used to produce an image of the volcano data,
I disagree. A "rect" grob is a vector object and a "raster" grob is a raster object and I think they should be kept distinct. You could possibly create a higher-level "image" object that is agnostic with respect to how it is implemented and have both "rect"-based and "raster"-based versions of that, but "rect" and "raster" are graphical primitives and at that level I think the distinction is useful.
Paul
d <- volcano cols <- grey(t(d)/max(c(d))) xy <- expand.grid(x=seq(0, 1, length=ncol(d)), y=seq(0, 1, length=nrow(d))) pdf("comparison.pdf", width=10, height=10/2*ncol(d)/nrow(d)) pushViewport(viewport(layout=grid.layout(1, 2))) pushViewport(viewport(layout.pos.r=1, layout.pos.c=1)) grid.rect(xy$y, rev(xy$x), 1/(nrow(d)), 1/(ncol(d)), gp=gpar(col=NA, fill=cols)) grid.text("grid.rect") upViewport() pushViewport(viewport(layout.pos.r=1, layout.pos.c=2)) cols.mat <- matrix(cols, ncol=ncol(d), byrow=T) grid.raster(t(cols.mat)) grid.text("grid.raster") dev.off() Of course grid.raster provides a much better output in terms of file size, speed, visualisation artifacts, and interpolation. My question though: is it necessary to have a distinct grob for raster output? Couldn't "raster" be an option in grid.rect when the width and height are constant? Alternatively, it might be useful to provide a function that converts a rectGrob into a rasterGrob, rect2raster <- function(g){ with(g, rasterGrob(matrix(gp$fill, ncol=length(unique(x))), mean(x),mean(y))) } This way, much of the existing code relying on grid.rect (e.g in lattice or ggplot2) could easily be adapted to work with grid.raster in favorable cases. Best regards, baptiste 2009/12/1 Paul Murrell <p.murr...@auckland.ac.nz>:Hi This is for developers of extension packages that provide extra *graphics devices* for R. In the *development* version of R, support has been added to the graphics engine for sending raster images (bitmaps) to a graphics device. This consists mainly of two new device functions: dev_Raster() and dev_Cap(). The R_GE_version constant (in GraphicsEngine.h) has been bumped up to 6 as a marker of this change. This means that, at a minimum, all graphics devices should be updated to provide dummy implementations of these new functions that just say the feature is not yet implemented (see for example the PicTeX and XFig devices in the 'grDevices' package). A full implementation of dev_Raster() should be able to draw a raster image (provided as an array of 32-bit R colors) at any size, possibly (bilinear) interpolated (otherwise nearest-neighbour), at any orientation, and with a per-pixel alpha channel. Where these are not natively supported by a device, the graphics engine provides some routines for scaling and rotating raster images (see for example the X11 device). The dev_Cap() function should return a representation of a raster image captured from the current device. This will only make sense for some devices (see for example the Cairo device in the 'grDevices' package). A little more information and a couple of small examples are provided at http://developer.r-project.org/Raster/raster-RFC.html Paul -- Dr Paul Murrell Department of Statistics The University of Auckland Private Bag 92019 Auckland New Zealand 64 9 3737599 x85392 p...@stat.auckland.ac.nz http://www.stat.auckland.ac.nz/~paul/ ______________________________________________ R-devel@r-project.org mailing list https://stat.ethz.ch/mailman/listinfo/r-devel
-- Dr Paul Murrell Department of Statistics The University of Auckland Private Bag 92019 Auckland New Zealand 64 9 3737599 x85392 p...@stat.auckland.ac.nz http://www.stat.auckland.ac.nz/~paul/ ______________________________________________ R-devel@r-project.org mailing list https://stat.ethz.ch/mailman/listinfo/r-devel
