Add Shiny output binding with g2output() and renderG2()

DESCRIPTION

@@ -1,6 +1,6 @@
 Package: gglite
 Title: Lightweight Data Visualization via the Grammar of Graphics
-Version: 0.0.2
+Version: 0.0.3
 Authors@R: person("Yihui", "Xie", role = c("aut", "cre"), email = "xie@yihui.name",
     comment = c(ORCID = "0000-0003-0645-5666"))
 Description: A lightweight R interface to the AntV G2 JavaScript visualization
@@ -13,8 +13,10 @@ Depends: R (>= 4.1.0)
 Imports:
     xfun
 Suggests:
+    htmltools,
     litedown,
     knitr,
+    shiny,
     testit
 Encoding: UTF-8
 Roxygen: list(markdown = TRUE)

NAMESPACE

@@ -11,6 +11,7 @@ export(encode)
 export(facet_circle)
 export(facet_rect)
 export(g2)
+export(g2Output)
 export(interact)
 export(labels_of)
 export(legend_of)
@@ -50,7 +51,7 @@ export(mark_treemap)
 export(mark_vector)
 export(mark_word_cloud)
 export(preview)
-export(render_shiny)
+export(renderG2)
 export(scale_of)
 export(scrollbar_of)
 export(slider_of)

R/render.R

@@ -175,16 +175,3 @@ record_print.g2 = function(x, ...) {
   }
 }
 
-#' Render a Chart in Shiny
-#'
-#' @param chart A `g2` object.
-#' @param session The Shiny session object.
-#' @param output_id The container element ID on the client side.
-#' @export
-render_shiny = function(chart, session, output_id) {
-  spec = build_config(chart)
-  ctor = chart$options
-  session$sendCustomMessage('g2-render', list(
-    id = output_id, ctor = ctor, spec = spec
-  ))
-}

R/shiny.R

@@ -0,0 +1,65 @@
+#' Shiny Output for a G2 Chart
+#'
+#' Create a placeholder in the UI for a G2 chart rendered by [renderG2()].
+#' The required JavaScript dependencies (G2 library, column-major data helper,
+#' and output binding) are automatically attached to the page.
+#'
+#' @param outputId Output variable name to read the chart from.
+#' @param width,height CSS dimensions for the chart container.
+#' @return A Shiny UI element.
+#' @examples
+#' \dontrun{
+#' library(shiny)
+#' ui = fluidPage(g2Output('chart1'))
+#' server = function(input, output, session) {
+#'   output$chart1 = renderG2({
+#'     g2(mtcars, x = 'mpg', y = 'hp') |> mark_point()
+#'   })
+#' }
+#' shinyApp(ui, server)
+#' }
+#' @export
+g2Output = function(outputId, width = '100%', height = '480px') {
+  dep_g2 = htmltools::htmlDependency(
+    'g2', '5',
+    src = c(href = 'https://unpkg.com/@antv/g2@5/dist'),
+    script = 'g2.min.js'
+  )
+  dep_col = htmltools::htmlDependency(
+    'g2-column', '1',
+    src = c(href = 'https://cdn.jsdelivr.net/npm/@xiee/utils/js'),
+    script = 'g2-column.min.js'
+  )
+  dep_binding = htmltools::htmlDependency(
+    'g2-binding', as.character(utils::packageVersion('gglite')),
+    src = system.file('www', package = 'gglite'),
+    script = 'g2-binding.js'
+  )
+  shiny::tagList(
+    dep_g2, dep_col, dep_binding,
+    shiny::div(
+      id = outputId, class = 'gglite-output',
+      style = paste0('width:', width, ';height:', height)
+    )
+  )
+}
+
+#' Render a G2 Chart in Shiny
+#'
+#' Create a reactive G2 chart for use with [g2Output()].
+#' Assign it to an output slot: `output$ID = renderG2({...})`.
+#'
+#' @param expr An expression that returns a `g2` object.
+#' @param env The environment in which to evaluate `expr`.
+#' @param quoted Whether `expr` is already quoted.
+#' @return A render function for use with [g2Output()].
+#' @export
+renderG2 = function(expr, env = parent.frame(), quoted = FALSE) {
+  if (!quoted) expr = substitute(expr)
+  expr_env = env
+  func = function() eval(expr, envir = expr_env)
+  shiny::markRenderFunction(g2Output, function() {
+    chart = func()
+    list(ctor = chart$options, spec = xfun::tojson(build_config(chart)))
+  })
+}

examples/shiny.Rmd

@@ -0,0 +1,86 @@
+---
+title: Shiny
+---
+
+gglite charts can be embedded in [Shiny](https://shiny.posit.co/) applications
+using `g2Output()` and `renderG2()`. These follow the familiar Shiny output/
+render pattern: `g2Output()` creates the placeholder in the UI and
+automatically injects the required JavaScript dependencies, while `renderG2()`
+creates the reactive chart in the server.
+
+## Basic Example
+
+The simplest app renders a static scatter plot:
+
+```r
+library(shiny)
+library(gglite)
+
+ui = fluidPage(
+  g2Output('chart1')
+)
+
+server = function(input, output, session) {
+  output$chart1 = renderG2({
+    g2(mtcars, x = 'mpg', y = 'hp') |> mark_point()
+  })
+}
+
+shinyApp(ui, server)
+```
+
+## Reactive Example
+
+Wrap the chart in `renderG2({})` and reference reactive inputs directly. The
+chart re-renders automatically whenever an input changes. The following app
+lets the user pick the y-axis variable:
+
+```r
+library(shiny)
+library(gglite)
+
+ui = fluidPage(
+  selectInput('xvar', 'X variable',
+              choices = c('hp', 'wt', 'qsec', 'drat')),
+  g2Output('chart1')
+)
+
+server = function(input, output, session) {
+  output$chart1 = renderG2({
+    g2(mtcars, x = input$xvar, y = 'mpg') |>
+      mark_point() |>
+      title_of(paste('mpg vs', input$xvar))
+  })
+}
+
+shinyApp(ui, server)
+```
+
+## Multiple Charts
+
+Use a distinct `outputId` for each chart and assign a separate `renderG2()`
+for each one:
+
+```r
+library(shiny)
+library(gglite)
+
+ui = fluidPage(
+  fluidRow(
+    column(6, g2Output('scatter')),
+    column(6, g2Output('bars'))
+  )
+)
+
+server = function(input, output, session) {
+  output$scatter = renderG2({
+    g2(mtcars, x = 'mpg', y = 'hp') |> mark_point()
+  })
+  output$bars = renderG2({
+    freq = as.data.frame(table(cyl = mtcars$cyl))
+    g2(freq, x = 'cyl', y = 'Freq') |> mark_interval()
+  })
+}
+
+shinyApp(ui, server)
+```

inst/www/g2-binding.js

@@ -0,0 +1,29 @@
+// Shiny output binding for gglite / AntV G2 charts
+'use strict';
+
+$(document).ready(function() {
+  const g2OutputBinding = new Shiny.OutputBinding();
+  Object.assign(g2OutputBinding, {
+    find: function(scope) {
+      return $(scope).find('.gglite-output');
+    },
+    renderValue: function(el, data) {
+      if (!data) return;
+      if (el._g2chart) {
+        el._g2chart.destroy();
+        el._g2chart = null;
+      }
+      const ctor = Object.assign({}, data.ctor, { container: el.id });
+      const spec = data.spec;  // already parsed (Shiny embeds xfun JSON as object)
+      const chart = new G2.Chart(ctor);
+      chart.options(spec);
+      chart.render();
+      el._g2chart = chart;
+    },
+    renderError: function(el, err) {
+      console.error('gglite:', err.message);
+    }
+  });
+
+  Shiny.outputBindings.register(g2OutputBinding, 'gglite.g2');
+});