1 ```handle_xy <- function(xy) { ``` 2 1 ``` if (is.list(xy) && length(xy) == 2L) xy <- stats::setNames(xy, c("x", "y")) ``` 3 1 ``` if (is.list(xy)) xy <- do.call(cbind, xy) ``` 4 1 ``` if (!dim(xy)[2L] == 2L) warning("expected two columns, x/y") ``` 5 1 ``` if (dim(xy)[2L] < 2L) stop("expected two columns, x/y") ``` 6 1 ``` if (dim(xy)[1L] < 3L) warning("fewer than 3 coordinates supplied") ``` 7 1 ``` xy ``` 8 ```} ``` 9 10 ```#' Constrained polygon triangulation ``` 11 ```#' ``` 12 ```#' Produce a triangulation index into x,y coordinates of a polygon ``` 13 ```#' that may include holes. Holes are specified by input argument `holes` ``` 14 ```#' which marks the starting index of each hole, if any. ``` 15 ```#' ``` 16 ```#' Ear cutting (or ear clipping) applies constrained triangulation by ``` 17 ```#' successively 'cutting' triangles from a polygon defined by path/s. Holes are supported, the earcut library works with ``` 18 ```#' single-island-with-holes polygons, analogous to the POLYGON type in simple features. ``` 19 ```#' ``` 20 ```#' To understand the specification of holes, see the examples with comment ``` 21 ```#' starting "1) Notice how the hole begins ..." in relation to the example code. ``` 22 ```#' @param xy xy-coordinates, either a list, matrix, or data frame ``` 23 ```#' @param holes index of starting position of each hole in x,y, leave set to `0` if no holes ``` 24 ```#' @param ... unused ``` 25 ```#' @return integer vector of triangle index, in sets of three ``` 26 ```#' @export ``` 27 ```#' @seealso plot_ears ``` 28 ```#' @examples ``` 29 ```#' ## single ring polygon ``` 30 ```#' x <- c(0, 0, 0.75, 1, 0.5, 0.8, 0.69) ``` 31 ```#' y <- c(0, 1, 1, 0.8, 0.7, 0.6, 0) ``` 32 ```#' (ind <- earcut(cbind(x, y))) ``` 33 ```#' plot_ears(cbind(x, y), ind) ``` 34 ```#' ``` 35 ```#' ## polygon with a hole ``` 36 ```#' x <- c(0, 0, 0.75, 1, 0.5, 0.8, 0.69, ``` 37 ```#' 0.2, 0.5, 0.5, 0.3, 0.2) ``` 38 ```#' y <- c(0, 1, 1, 0.8, 0.7, 0.6, 0, ``` 39 ```#' 0.2, 0.2, 0.4, 0.6, 0.4) ``` 40 ```#' ind <- earcut(cbind(x, y), holes = 8) ``` 41 ```#' plot_ears(cbind(x, y), ind) ``` 42 ```#' ``` 43 ```#' ## 1) Notice how the hole begins at index 8, ``` 44 ```#' ## hence holes = 8 above, and holes = c(8, 13) below ``` 45 ```#' plot_ears(cbind(x, y), ind, col = "grey", border = NA) ``` 46 ```#' text(x, y, labels = seq_along(x), pos = 2) ``` 47 ```#' ``` 48 ```#' ## add another hole ``` 49 ```#' x <- c(0, 0, 0.75, 1, 0.5, 0.8, 0.69, ``` 50 ```#' 0.2, 0.5, 0.5, 0.3, 0.2, ``` 51 ```#' 0.15, 0.23, 0.2) ``` 52 ```#' y <- c(0, 1, 1, 0.8, 0.7, 0.6, 0, ``` 53 ```#' 0.2, 0.2, 0.4, 0.6, 0.4, ``` 54 ```#' 0.65, 0.65, 0.81) ``` 55 ```#' ind <- earcut(cbind(x, y), holes = c(8, 13)) ``` 56 ```#' plot_ears(cbind(x, y), ind, col = "grey") ``` 57 58 ```#' # simpler shape with more than one hole ``` 59 ```#' # the two inside holes are open to each other ``` 60 ```#' # (so we can use the same data for one hole or two) ``` 61 ```#' x <- c(0, 0, 1, 1, ``` 62 ```#' 0.4, 0.2, 0.2, 0.4, ``` 63 ```#' 0.6, 0.8, 0.8, 0.6 ``` 64 ```#' ) ``` 65 ```#' y <- c(0, 1, 1, 0, ``` 66 ```#' 0.2, 0.2, 0.4, 0.4, ``` 67 ```#' 0.6, 0.6, 0.4, 0.4 ``` 68 ```#' ) ``` 69 ```#' ind <- decido::earcut(cbind(x, y), holes = c(5, 9)) ``` 70 ```#' plot_ears(cbind(x, y), ind, col = "grey") ``` 71 ```#' plot_holes(cbind(x, y), holes = c(5, 9), col = "grey") ``` 72 ```#' ind <- decido::earcut(cbind(x, y), holes = 5) ``` 73 ```#' plot_ears(cbind(x, y), ind, col = "grey") ``` 74 ```#' plot_holes(cbind(x, y), holes = 5, col = "grey") ``` 75 ```earcut <- function(xy, holes = 0, ...) { ``` 76 1 ``` UseMethod("earcut") ``` 77 ```} ``` 78 ```#' @name earcut ``` 79 ```#' @export ``` 80 ```earcut.default <- function(xy, holes = 0L, ...) { ``` 81 1 ``` xy <- handle_xy(xy) ``` 82 1 ``` x <- xy[ ,1L] ``` 83 1 ``` y <- xy[ ,2L] ``` 84 ``` ## convert holes to C++ 0-based ``` 85 1 ``` if (any(holes < 0)) stop("'holes' must be zero, or a vector of positive vaues") ``` 86 1 ``` if (any(holes < 1) && length(holes) > 1) stop("cannot mix index 0 with non-zero for 'holes'") ``` 87 1 ``` if (any(holes < 4) && length(holes) > 1) stop("no hole can begin before element 4") ``` 88 1 ``` if (any(holes > (length(x) - 2))) stop("no hole can begin later than 3 elements from the end") ``` 89 1 ``` nholes <- length(holes) ``` 90 1 ``` if (holes[1] == 0) { ``` 91 ``` ## a nonsense situation, so we reset to be sure ``` 92 1 ``` nholes <- 0L ``` 93 1 ``` holes <- 0L ``` 94 ``` } ``` 95 1 ``` earcut_cpp(x, y, holes = as.integer(holes - 1), numholes = as.integer(nholes)) + 1L ``` 96 ```} ``` 97 ```#' Plot ears or polygons ``` 98 ```#' ``` 99 ```#' Plot the triangles produced by [earcut], or plot the polygon paths ``` 100 ```#' using the same interface as earcut uses. This allows for easy ``` 101 ```#' comparison and checking of what the results should be. ``` 102 ```#' ``` 103 ```#' For both functions the first input is ``` 104 ```#' a matrix of x,y coordinates. ``` 105 ```#' ``` 106 ```#' For [plot_ears] the second input is ``` 107 ```#' the index output of earcut. The index is treated in sets of 3 values, with ``` 108 ```#' individual calls to [polypath] to draw a polygon for each triangle. ``` 109 ```#' ``` 110 ```#' For [plot_holes] the second input is the `holes` argument that would ``` 111 ```#' be used for earcut. This is used to split the coordinates at these positions, ``` 112 ```#' inserting `NA` values as per the mechanism used by [graphics::polypath] to ``` 113 ```#' break coordinates into separate polygon rings. (There's no winding rule here ``` 114 ```#' plot_rules is hard-coded to always use the evenodd rule, so that winding ``` 115 ```#' order may be ignored). ``` 116 ```#' @param xy xy-coordinates, either a list, matrix, or data frame ``` 117 ```#' @param idx index of triangles ``` 118 ```#' @param holes index of starting position of holes (see [earcut]) ``` 119 ```#' @param add add to current plot, or create a new ``` 120 ```#' @param ... arguments to polypath ``` 121 ```#' @export ``` 122 ```#' @importFrom graphics plot polypath ``` 123 ```#' @seealso earcut ``` 124 ```#' @examples ``` 125 ```#' ## after ?polypath ``` 126 ```#' x <- cbind(c(.1, .1, .9, .9, .2, .2, .8, .8), ``` 127 ```#' c(.1, .9, .9, .1, .2, .8, .8, .2)) ``` 128 ```#' plot_holes(x, holes = 5, col = "grey") ``` 129 ```plot_ears <- function(xy, idx, add = FALSE, ...) { ``` 130 1 ``` xy <- handle_xy(xy) ``` 131 1 ``` if (!add) plot(xy, asp = 1) ``` 132 1 ``` apply(matrix(idx, 3), 2, function(i) polypath(xy[i, ], ...)) ``` 133 1 ``` invisible(NULL) ``` 134 ```} ``` 135 136 ```#' @name plot_ears ``` 137 ```#' @export ``` 138 ```plot_holes <- function(xy, holes = 0, add = FALSE, ...) { ``` 139 1 ``` xy <- handle_xy(xy) ``` 140 1 ``` if (holes[1] > 0) { ``` 141 1 ``` g <- c(0, cumsum(abs(diff(seq_len(nrow(xy)) %in% holes)))) ``` 142 1 ``` g[holes] <- g[holes] + 1 ``` 143 1 ``` g <- as.integer(factor(g)) ``` 144 1 ``` xy <- utils::head(do.call(rbind, lapply(split(as.data.frame(xy), g), function(itab) rbind(itab, NA))), -1L) ``` 145 146 ``` } ``` 147 148 1 ``` if (!add) plot(xy, type = "n", asp = 1) ``` 149 1 ``` polypath(xy, rule = "evenodd", ...) ``` 150 1 ``` invisible(NULL) ``` 151 ```} ```

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