| Working with Viewports {grid} | R Documentation |
Grid maintains a tree of viewports — nested drawing contexts.
These functions provide ways to add or remove viewports and to navigate amongst viewports in the tree.
pushViewport(..., recording=TRUE) popViewport(n, recording=TRUE) downViewport(name, strict=FALSE, recording=TRUE) seekViewport(name, recording=TRUE) upViewport(n, recording=TRUE)
... |
One or more objects of class "viewport". |
n |
An integer value indicating how many viewports to
pop or navigate up. The special value 0 indicates to
pop or navigate viewports right up to the root viewport. |
name |
A character value to identify a viewport in the tree. |
strict |
A boolean indicating whether the vpPath must be matched exactly. |
recording |
A logical value to indicate whether the viewport operation should be recorded on the Grid display list. |
Objects created by the viewport() function are only
descriptions
of a drawing context. A viewport object must be pushed onto the
viewport tree before it has any effect on drawing.
The viewport tree always has a single root viewport (created by the
system) which corresponds to the entire device (and default
graphical parameter settings). Viewports may be added to the tree
using pushViewport() and removed from the tree using
popViewport().
There is only ever one current viewport, which is the current
position within the viewport tree. All drawing and
viewport operations are relative to the current viewport.
When a viewport is pushed it becomes the current viewport.
When a viewport is popped, the parent viewport becomes
the current viewport. Use upViewport to navigate to the parent
of the current viewport, without removing the current viewport
from the viewport tree. Use downViewport to navigate to
a viewport further down the viewport tree and seekViewport
to navigate to a viewport anywhere else in the tree.
If a viewport is pushed and it has the same name as a
viewport at the same level in the tree, then it replaces the
existing viewport in the tree.
downViewport returns the number of viewports it went down.
This can be useful for returning to your starting point by doing
something like depth <- downViewport() then
upViewport(depth).
Paul Murrell
# push the same viewport several times
grid.newpage()
vp <- viewport(width=0.5, height=0.5)
pushViewport(vp)
grid.rect(gp=gpar(col="blue"))
grid.text("Quarter of the device",
y=unit(1, "npc") - unit(1, "lines"), gp=gpar(col="blue"))
pushViewport(vp)
grid.rect(gp=gpar(col="red"))
grid.text("Quarter of the parent viewport",
y=unit(1, "npc") - unit(1, "lines"), gp=gpar(col="red"))
popViewport(2)
# push several viewports then navigate amongst them
grid.newpage()
grid.rect(gp=gpar(col="grey"))
grid.text("Top-level viewport",
y=unit(1, "npc") - unit(1, "lines"), gp=gpar(col="grey"))
if (interactive()) Sys.sleep(1.0)
pushViewport(viewport(width=0.8, height=0.7, name="A"))
grid.rect(gp=gpar(col="blue"))
grid.text("1. Push Viewport A",
y=unit(1, "npc") - unit(1, "lines"), gp=gpar(col="blue"))
if (interactive()) Sys.sleep(1.0)
pushViewport(viewport(x=0.1, width=0.3, height=0.6,
just="left", name="B"))
grid.rect(gp=gpar(col="red"))
grid.text("2. Push Viewport B (in A)",
y=unit(1, "npc") - unit(1, "lines"), gp=gpar(col="red"))
if (interactive()) Sys.sleep(1.0)
upViewport(1)
grid.text("3. Up from B to A",
y=unit(1, "npc") - unit(2, "lines"), gp=gpar(col="blue"))
if (interactive()) Sys.sleep(1.0)
pushViewport(viewport(x=0.5, width=0.4, height=0.8,
just="left", name="C"))
grid.rect(gp=gpar(col="green"))
grid.text("4. Push Viewport C (in A)",
y=unit(1, "npc") - unit(1, "lines"), gp=gpar(col="green"))
if (interactive()) Sys.sleep(1.0)
pushViewport(viewport(width=0.8, height=0.6, name="D"))
grid.rect()
grid.text("5. Push Viewport D (in C)",
y=unit(1, "npc") - unit(1, "lines"))
if (interactive()) Sys.sleep(1.0)
upViewport(0)
grid.text("6. Up from D to top-level",
y=unit(1, "npc") - unit(2, "lines"), gp=gpar(col="grey"))
if (interactive()) Sys.sleep(1.0)
downViewport("D")
grid.text("7. Down from top-level to D",
y=unit(1, "npc") - unit(2, "lines"))
if (interactive()) Sys.sleep(1.0)
seekViewport("B")
grid.text("8. Seek from D to B",
y=unit(1, "npc") - unit(2, "lines"), gp=gpar(col="red"))
pushViewport(viewport(width=0.9, height=0.5, name="A"))
grid.rect()
grid.text("9. Push Viewport A (in B)",
y=unit(1, "npc") - unit(1, "lines"))
if (interactive()) Sys.sleep(1.0)
seekViewport("A")
grid.text("10. Seek from B to A (in ROOT)",
y=unit(1, "npc") - unit(3, "lines"), gp=gpar(col="blue"))
if (interactive()) Sys.sleep(1.0)
seekViewport(vpPath("B", "A"))
grid.text("11. Seek from\nA (in ROOT)\nto A (in B)")
popViewport(0)