R/alphaMaskGrob.R

In gridpattern: 'grid' Pattern Grobs

#' Mask grob using another grob to specify the (alpha) mask
#'
#' `alphaMaskGrob()` masks a grob using another grob to specify the (alpha) mask.
#'
#' @param maskee Grob to be masked
#' @param masker Grob that defines masking region
#' @param use_R4.1_masks If `TRUE` use the grid mask feature introduced in R v4.1.0.
#'                       If `FALSE` do a `rasterGrob` approximation.
#'                       If `NULL` try to guess an appropriate choice.
#'                       Note not all graphic devices support the grid mask feature.
#' @param png_device \dQuote{png} graphics device to save intermediate raster data with if `use_R4.1_masks` is `FALSE`.
#'                   If `NULL` and suggested package `ragg` is available
#'                   and versions are high enough we directly capture masked raster via [ragg::agg_capture()].
#'                   Otherwise we will use `png_device`
#'                   (default [ragg::agg_png()] if available else [grDevices::png()]) and [png::readPNG()]
#'                   to manually compute a masked raster.
#' @param res Resolution of desired `rasterGrob` in pixels per inch if `use_R4.1_masks` is `FALSE`.
#' @return A `grid` grob
#' @inheritParams grid::polygonGrob
#' @examples
#'   \donttest{# May take more than 5 seconds on CRAN servers
#'   if (capabilities("png") && require("grid")) {
#'     maskee <- patternGrob("circle", gp = gpar(col = "black", fill = "yellow"),
#'                            spacing = 0.1, density = 0.5)
#'     angle <- seq(2 * pi / 4, by = 2 * pi / 6, length.out = 7)
#'     x_hex_outer <- 0.5 + 0.5 * cos(angle)
#'     y_hex_outer <- 0.5 + 0.5 * sin(angle)
#'     x_hex_inner <- 0.5 + 0.25 * cos(rev(angle))
#'     y_hex_inner <- 0.5 + 0.25 * sin(rev(angle))
#'     gp <- gpar(lwd = 0, col = NA, fill = "white")
#'     masker <- grid::pathGrob(x = c(x_hex_outer, x_hex_inner),
#'                              y = c(y_hex_outer, y_hex_inner),
#'                              id = rep(1:2, each = 7),
#'                              rule = "evenodd", gp = gp)
#'     masked <- alphaMaskGrob(maskee, masker, use_R4.1_masks = FALSE)
#'     grid.draw(masked)
#'   }
#'   if (capabilities("png") && require("grid")) {
#'     maskee_transparent <- rectGrob(gp = gpar(col = NA, fill = "blue"))
#'     gp <- gpar(lwd = 20, col = "black", fill = grDevices::rgb(0, 0, 0, 0.5))
#'     masker_transparent <- editGrob(masker, gp = gp)
#'     masked_transparent <- alphaMaskGrob(maskee_transparent,
#'                                         masker_transparent,
#'                                         use_R4.1_masks = FALSE)
#'     grid.newpage()
#'     grid.draw(masked_transparent)
#'   }
#'   }
#' @export
alphaMaskGrob <- function(
	maskee,
	masker,
	use_R4.1_masks = getOption(
		"ggpattern_use_R4.1_masks",
		getOption("ggpattern_use_R4.1_features")
	),
	png_device = NULL,
	res = getOption("ggpattern_res", 72),
	name = NULL,
	gp = gpar(),
	vp = NULL
) {
	gTree(
		maskee = maskee,
		masker = masker,
		use_R4.1_masks = use_R4.1_masks,
		res = res,
		png_device = png_device,
		name = name,
		gp = gp,
		vp = vp,
		cl = "alpha_mask"
	)
}

# Avoid R CMD check WARNING on R 4.0 which lacks `mask` argument
vport <- function(...) viewport(...)

#' @export
makeContent.alpha_mask <- function(x) {
	current_dev <- grDevices::dev.cur()
	on.exit(grDevices::dev.set(current_dev))

	use_R4.1_masks <- x$use_R4.1_masks
	if (is.null(use_R4.1_masks)) {
		use_R4.1_masks <- guess_has_R4.1_features("masks")
	} else {
		use_R4.1_masks <- as.logical(use_R4.1_masks)
	}

	stopifnot(getRversion() >= '4.1.0' || !use_R4.1_masks)

	if (use_R4.1_masks) {
		grob <- grobTree(x$maskee, vp = vport(mask = x$masker), name = "alpha_mask")
	} else if (
		is.null(x$png_device) &&
			getRversion() >= '4.1.0' &&
			requireNamespace("ragg", quietly = TRUE) &&
			packageVersion("ragg") >= '1.2.0'
	) {
		grob <- gridpattern_mask_agg_capture(x$maskee, x$masker, x$res)
	} else {
		png_device <- x$png_device %||% default_png_device()
		if (device_supports_masks(png_device)) {
			grob <- gridpattern_mask_raster_straight(x$maskee, x$masker, x$res, png_device)
		} else {
			grob <- gridpattern_mask_raster_manual(x$maskee, x$masker, x$res, png_device)
		}
	}

	gl <- gList(grob)
	setChildren(x, gl)
}

device_supports_masks <- function(png_device) {
	current_dev <- grDevices::dev.cur()
	if (current_dev > 1) {
		on.exit(grDevices::dev.set(current_dev))
	}
	png_file <- tempfile(fileext = ".png")
	on.exit(unlink(png_file), add = TRUE)
	png_device(png_file)
	value <- guess_has_R4.1_features("masks")
	dev.off()
	value
}

gridpattern_mask_agg_capture <- function(maskee, masker, res) {
	current_dev <- grDevices::dev.cur()
	if (current_dev > 1) {
		on.exit(grDevices::dev.set(current_dev))
	}
	height <- res * convertHeight(unit(1, "npc"), "in", valueOnly = TRUE)
	width <- res * convertWidth(unit(1, "npc"), "in", valueOnly = TRUE)

	ragg::agg_capture(height = height, width = width, res = res, bg = "transparent")
	grob <- alphaMaskGrob(maskee, masker, use_R4.1_masks = TRUE)
	grid.draw(grob)
	raster_masked <- dev.capture(native = FALSE)
	dev.off()
	grid::rasterGrob(raster_masked)
}

default_png_device <- function() {
	if (requireNamespace("ragg", quietly = TRUE)) {
		ragg::agg_png
	} else {
		stopifnot(capabilities("png"))
		grDevices::png
	}
}

gridpattern_mask_raster_straight <- function(maskee, masker, res, png_device) {
	current_dev <- grDevices::dev.cur()
	if (current_dev > 1) {
		on.exit(grDevices::dev.set(current_dev))
	}
	height <- res * convertHeight(unit(1, "npc"), "in", valueOnly = TRUE)
	width <- res * convertWidth(unit(1, "npc"), "in", valueOnly = TRUE)

	png_masked <- tempfile(fileext = ".png")
	on.exit(unlink(png_masked), add = TRUE)
	png_device(png_masked, height = height, width = width, res = res, bg = "transparent")
	grob <- alphaMaskGrob(maskee, masker, use_R4.1_masks = TRUE)
	grid.draw(grob)
	dev.off()

	raster_masked <- png::readPNG(png_masked, native = FALSE)
	grid::rasterGrob(raster_masked)
}

gridpattern_mask_raster_manual <- function(maskee, masker, res, png_device) {
	current_dev <- grDevices::dev.cur()
	if (current_dev > 1) {
		on.exit(grDevices::dev.set(current_dev))
	}
	height <- res * convertHeight(unit(1, "npc"), "in", valueOnly = TRUE)
	width <- res * convertWidth(unit(1, "npc"), "in", valueOnly = TRUE)

	png_maskee <- tempfile(fileext = ".png")
	on.exit(unlink(png_maskee), add = TRUE)
	png_device(png_maskee, height = height, width = width, res = res, bg = "transparent")
	grid.draw(maskee)
	dev.off()

	png_masker <- tempfile(fileext = ".png")
	on.exit(unlink(png_masker), add = TRUE)
	png_device(png_masker, height = height, width = width, res = res, bg = "transparent")
	grid.draw(masker)
	dev.off()

	raster_maskee <- png::readPNG(png_maskee, native = FALSE)
	raster_masker <- png::readPNG(png_masker, native = FALSE)

	stopifnot(
		length(dim(raster_maskee)) == 3L,
		length(dim(raster_masker)) == 3L,
		dim(raster_maskee)[3L] >= 3L,
		dim(raster_masker)[3L] >= 3L
	)
	if (dim(raster_maskee)[3L] < 4L) {
		raster_maskee <- add_alpha_channel(raster_maskee)
	}
	if (dim(raster_masker)[3L] < 4L) {
		raster_masker <- add_alpha_channel(raster_masker)
	}

	raster_masked <- raster_maskee
	raster_masked[,, 4L] <- raster_maskee[,, 4L] * raster_masker[,, 4L]

	rasterGrob(raster_masked, name = "alpha_mask")
}

add_alpha_channel <- function(a) {
	a_ <- array(NA, dim = c(dim(a)[1], dim(a)[2], 4L))
	a_[,, -4L] <- a
	a_[,, 4L] <- 1.
	a_
}