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Draw to a buffer that can be accessed directly

Source: R/agg_dev.R
agg_capture.Rd

Usually the point of using a graphic device is to create a file or show the graphic on the screen. A few times we need the image data for further processing in R, and instead of writing it to a file and then reading it back into R the agg_capture() device lets you get the image data directly from the buffer. In contrast to the other devices this device returns a function, that when called will return the current state of the buffer.

Usage

agg_capture(
  width = 480,
  height = 480,
  units = "px",
  pointsize = 12,
  background = "white",
  res = 72,
  scaling = 1,
  snap_rect = TRUE,
  bg
)

Arguments

width, height

The dimensions of the device

units

The unit width and height is measured in, in either pixels ('px'), inches ('in'), millimeters ('mm'), or centimeter ('cm').

pointsize

The default pointsize of the device in pt. This will in general not have any effect on grid graphics (including ggplot2) as text size is always set explicitly there.

background

The background colour of the device

res

The resolution of the device. This setting will govern how device dimensions given in inches, centimeters, or millimeters will be converted to pixels. Further, it will be used to scale text sizes and linewidths

scaling

A scaling factor to apply to the rendered line width and text size. Useful for getting the right dimensions at the resolution that you need. If e.g. you need to render a plot at 4000x3000 pixels for it to fit into a layout, but you find that the result appears to small, you can increase the scaling argument to make everything appear bigger at the same resolution.

snap_rect

Should axis-aligned rectangles drawn with only fill snap to the pixel grid. This will prevent anti-aliasing artifacts when two rectangles are touching at their border.

bg

Same as background for compatibility with old graphic device APIs

Value

A function that when called returns the current state of the buffer. The return value of the function depends on the native argument. If FALSE (default) the return value is a matrix of colour values and if TRUE the return value is a nativeRaster object.

Examples

cap <- agg_capture()
plot(1:10, 1:10)

# Get the plot as a matrix
raster <- cap()

# Get the plot as a nativeRaster
raster_n <- cap(native = TRUE)

dev.off()
#> agg_png 
#>       2 

# Look at the output
plot(as.raster(raster))