Pass on binwidth and height to geom

NEWS.md

@@ -1,5 +1,8 @@
 # ggplot2 (development version)
 
+* `geom_hex()` will now use the binwidth from `stat_bin_hex()` if present, 
+  instead of deriving it (@thomasp85, #4580)
+
 * Setting `stroke` to `NA` in `geom_point()` will no longer impair the sizing of
   the points (@thomasp85, #4624)
 

R/geom-hex.r

@@ -56,13 +56,31 @@ geom_hex <- function(mapping = NULL, data = NULL,
 GeomHex <- ggproto("GeomHex", Geom,
   draw_group = function(data, panel_params, coord, lineend = "butt",
                         linejoin = "mitre", linemitre = 10) {
+    if (empty(data)) {
+      return(zeroGrob())
+    }
     if (!inherits(coord, "CoordCartesian")) {
       abort("geom_hex() only works with Cartesian coordinates")
     }
+    # Extract binwidth and height from data if possible
+    if (!is.null(data$width)) {
+      data$xend <- data$x + data$width
+    }
+    if (!is.null(data$height)) {
+      data$yend <- data$y + data$height
+    }
 
     coords <- coord$transform(data, panel_params)
+
+    binwidth <- c(NA, NA)
+    if (!is.null(data$width)) {
+      binwidth[1] <- coords$xend[1] - coords$x[1]
+    }
+    if (!is.null(data$height)) {
+      binwidth[2] <- coords$yend[1] - coords$y[1]
+    }
     ggname("geom_hex", hexGrob(
-      coords$x, coords$y,
+      coords$x, coords$y, binwidth,
       gp = gpar(
         col = coords$colour,
         fill = alpha(coords$fill, coords$alpha),
@@ -97,11 +115,11 @@ GeomHex <- ggproto("GeomHex", Geom,
 # @param size vector of hex sizes
 # @param gp graphical parameters
 # @keyword internal
-hexGrob <- function(x, y, size = rep(1, length(x)), gp = gpar()) {
+hexGrob <- function(x, y, binwidth, size = rep(1, length(x)), gp = gpar()) {
   if (length(y) != length(x)) abort("`x` and `y` must have the same length")
 
-  dx <- resolution(x, FALSE)
-  dy <- resolution(y, FALSE) / sqrt(3) / 2 * 1.15
+  dx <- if (is.na(binwidth[1])) resolution(x, FALSE) else binwidth[1]/2
+  dy <- if (is.na(binwidth[2])) resolution(y, FALSE) / sqrt(3) / 2 * 1.15 else binwidth[2]/ sqrt(3) / 2
 
   hexC <- hexbin::hexcoords(dx, dy, n = 1)
 

R/hexbin.R

@@ -36,6 +36,8 @@ hexBinSummarise <- function(x, y, z, binwidth, fun = mean, fun.args = list(), dr
   # Convert to data frame
   out <- new_data_frame(hexbin::hcell2xy(hb))
   out$value <- as.vector(value)
+  out$width <- binwidth[1]
+  out$height <- binwidth[2]
 
   if (drop) out <- stats::na.omit(out)
   out

tests/testthat/test-geom-hex.R

@@ -18,3 +18,11 @@ test_that("size and linetype are applied", {
   expect_equal(gpar$lwd, c(4, 4) * .pt, tolerance = 1e-7)
   expect_equal(gpar$lty, c(2, 2), tolerance = 1e-7)
 })
+
+test_that("bin size are picked up from stat", {
+  expect_doppelganger("single hex bin with width and height of 0.1",
+    ggplot(data.frame(x = 0, y = 0)) +
+      geom_hex(aes(x = x, y = y), binwidth = c(0.1, 0.1)) +
+      coord_cartesian(xlim = c(-1, 1), ylim = c(-1, 1))
+  )
+})