Heatmap slow render on enabled dataLabels

Hi, first of all thanks for a great package! The proxy functions included in the develop version is really useful and it's easy to implement new proxies on top.

I however have a problem with the render time for heatmaps, when I set DataLabels = list(enabled = TRUE) for a Shiny app containing a lot of heatmaps.

I don't know if there exists a solution, but it seems like it's the rendering of DataLabels that is slowing the process down. When enabled = FALSE the render is a couple of seconds whereas for TRUE it's easy ~15 seconds.

I have found a original issue from the HighCharts JS package: https://stackoverflow.com/questions/43217023/highcharts-heatmap-chart-labels-render-extremely-slow. I've used the "solutinon" 2 and 3 but 4 is more of the back-end of the package.

library(dplyr)
library(shiny)
library(highcharter)
library(purrr)

data <- 
  dplyr::tibble(
    x = rep(1:48, 4),
    y = c(rep("A",48), rep("B", 48), rep("C", 48), rep("D", 48)),
    value = round(rnorm(48*4, mean = 200, sd = 10),2)
  )
number_of_plots <- 30
shinyApp(
  ui = fluidPage(
    purrr::map(1:number_of_plots, function(.x) {
      column(12, highcharter::highchartOutput(paste0("heatmap",.x), height = "100%"))
    })
  ),
  server = function(input, output) {

    purrr::walk(1:number_of_plots, .f = function(.x) {
      output[[paste0("heatmap",.x)]] <- 
        highcharter::renderHighchart({

          highcharter::highchart() %>%
            highcharter::hc_yAxis(categories = list("A", "B", "C", "D")) %>%
            highcharter::hc_xAxis(categories = data$x) %>%
            highcharter::hc_add_series(data = data,
                                       type = "heatmap",
                                       highcharter::hcaes(x, y, value),
                                       fast = TRUE) %>% 
            highcharter::hc_plotOptions(heatmap = list(
              dataLabels = list(
                enabled = TRUE,
                shadow = FALSE,
                align = "center",
                allowOverlap = TRUE,
                style = list(fontSize = "8px",
                             color = "black",
                             textOutline = NULL,
                             fontWeight = NULL
                )
              ),
              borderWidth = 0.5,
              borderColor = "#000000"
            )) %>% 
            highcharter::hc_chart(height = 135) %>% 
            highcharter::hc_legend(enabled = FALSE)
        })

    })
  }
)

sessionInfo :

R version 4.0.3 (2020-10-10)
Platform: x86_64-w64-mingw32/x64 (64-bit)
Running under: Windows 10 x64 (build 19042)

Matrix products: default

locale:
[1] LC_COLLATE=English_United Kingdom.1252  LC_CTYPE=English_United Kingdom.1252    LC_MONETARY=English_United Kingdom.1252 LC_NUMERIC=C                           
[5] LC_TIME=English_United Kingdom.1252    

attached base packages:
[1] stats     graphics  grDevices datasets  utils     methods   base     

other attached packages:
[1] purrr_0.3.4            highcharter_0.8.2.9000 shiny_1.6.0            dplyr_1.0.7           

loaded via a namespace (and not attached):
 [1] Rcpp_1.0.7        jquerylib_0.1.4   bslib_0.2.5.1     pillar_1.6.2      compiler_4.0.3    later_1.3.0       xts_0.12.1        remotes_2.4.0     tools_4.0.3      
[10] digest_0.6.27     lattice_0.20-41   jsonlite_1.7.2    lubridate_1.7.10  lifecycle_1.0.0   tibble_3.1.3      pkgconfig_2.0.3   rlang_0.4.11      igraph_1.2.6     
[19] cli_3.0.1         yaml_2.2.1        curl_4.3.2        fastmap_1.1.0     withr_2.4.2       stringr_1.4.0     sass_0.4.0        generics_0.1.0    vctrs_0.3.8      
[28] htmlwidgets_1.5.3 grid_4.0.3        tidyselect_1.1.1  data.table_1.14.0 glue_1.4.2        R6_2.5.1          fansi_0.5.0       TTR_0.24.2        tidyr_1.1.3      
[37] magrittr_2.0.1    backports_1.2.1   promises_1.2.0.1  ellipsis_0.3.2    htmltools_0.5.1.1 rlist_0.4.6.1     assertthat_0.2.1  quantmod_0.4.18   mime_0.11        
[46] xtable_1.8-4      renv_0.12.5       httpuv_1.6.2      utf8_1.2.2        stringi_1.7.3     cachem_1.0.6      broom_0.7.9       crayon_1.4.1      zoo_1.8-9

jbkunst / highcharter

Heatmap slow render on enabled dataLabels #723