R/rgba_float_to_rgba_int.R

In scattermore: Scatterplots with More Points

# This file is part of scattermore.
#
# Copyright (C) 2022 Mirek Kratochvil <exa.exa@gmail.com>
#               2022-2023 Tereza Kulichova <kulichova.t@gmail.com>
#
# scattermore is free software: you can redistribute it and/or modify
# it under the terms of the GNU General Public License as published by
# the Free Software Foundation, either version 3 of the License, or
# (at your option) any later version.
#
# scattermore is distributed in the hope that it will be useful,
# but WITHOUT ANY WARRANTY; without even the implied warranty of
# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
# GNU General Public License for more details.
#
# You should have received a copy of the GNU General Public License
# along with scattermore. If not, see <https://www.gnu.org/licenses/>.

#' rgba_float_to_rgba_int
#'
#' Convert a float RGBA bitmap with pre-multiplied alpha to integer RGBA bitmap.
#'
#' @param fRGBA RGBA bitmap in N-by-M-by-4 array.
#'
#' @return RGBA matrix. The output *is not premultiplied* by alpha.
#'
#' @export
#' @useDynLib scattermore, .registration=TRUE

rgba_float_to_rgba_int <- function(fRGBA) {
  if (!is.array(fRGBA) || dim(fRGBA)[3] != 4) stop("unsupported fRGBA format")

  A <- 255 / pmax(scattermore.globals$epsilon, fRGBA[, , 4]) # unpremultiply

  i32RGBA <- array(0L, dim(fRGBA))
  i32RGBA[, , 1] <- as.integer(fRGBA[, , 1] * A)
  i32RGBA[, , 2] <- as.integer(fRGBA[, , 2] * A)
  i32RGBA[, , 3] <- as.integer(fRGBA[, , 3] * A)
  i32RGBA[, , 4] <- as.integer(255 * fRGBA[, , 4])

  return(i32RGBA)
}