Can I change the cursor in plotly only when hovering over points?

Question

I want to change the default plotly cursor only when hovering over points

Example app

library(shiny)
library(plotly)

ui <- fluidPage(
  sidebarLayout(
    sidebarPanel(
      sliderInput("num_points", "Number of Points:", min = 2, max = 20, value = 10)
    ),
    mainPanel(
      plotlyOutput("line_plot")
    )
  )
)

server <- function(input, output, session) {
  output$line_plot <- renderPlotly({

    num_points <- input$num_points
    x <- 1:num_points
    y <- rnorm(num_points, mean = 5, sd = 2) 

    plot_ly(x = ~x, y = ~y, type = 'scatter', mode = 'lines+markers',
            line = list(color = 'blue'), marker = list(color = 'red', size = 10),
            hoverinfo = 'text', text = ~paste("X: ", x, "<br>Y: ", round(y, 2))) |>
      layout(
        title = "Line Plot with Points",
        xaxis = list(title = "X Axis"),
        yaxis = list(title = "Y Axis")
      )
  })
}

shinyApp(ui, server)

Answer 1

You can use htmlwidgets::onRender and implement JS to change the cursor style on plotly_hover event of your line_plot.

library(shiny)
library(plotly)

ui <- fluidPage(
 
  sidebarLayout(
    sidebarPanel(
      sliderInput("num_points", "Number of Points:", min = 2, max = 20, value = 10)
    ),
    mainPanel(
      plotlyOutput("line_plot")
    )
  )
)

server <- function(input, output, session) {
  output$line_plot <- renderPlotly({
    
    num_points <- input$num_points
    x <- 1:num_points
    y <- rnorm(num_points, mean = 5, sd = 2) 
    
    plot_ly(x = ~x, y = ~y, type = 'scatter', mode = 'lines+markers',
            line = list(color = 'blue'), marker = list(color = 'red', size = 10),
            hoverinfo = 'text', text = ~paste("X: ", x, "<br>Y: ", round(y, 2))) |>
      layout(
        title = "Line Plot with Points",
        xaxis = list(title = "X Axis"),
        yaxis = list(title = "Y Axis")
      ) %>%
      htmlwidgets::onRender(
          paste0(
            "function(el, x) {",
            "  function setCursor() {",
            "    var dragLayer = el.getElementsByClassName('nsewdrag')[0];",
            "    if (dragLayer) {",
            "      dragLayer.style.cursor = 'default';",
            "      el.on('plotly_hover', function(data) {",
            "        dragLayer.style.cursor = 'pointer';",
            "      });",
            "      el.on('plotly_unhover', function(data) {",
            "        dragLayer.style.cursor = 'default';",
            "      });",
            "      return true;",
            "    }",
            "    return false;",
            "  }",
            "  if (!setCursor()) {",
            "    var observer = new MutationObserver(function(mutations) {",
            "      if (setCursor()) { observer.disconnect(); }",
            "    });",
            "    observer.observe(el, { childList: true, subtree: true });",
            "  }",
            "}"
          )
      )
  })
}

shinyApp(ui, server)