Code Editor for app.R

library(shiny)
library(ggplot2)

ui <- fluidPage(
    titlePanel("Drawing App"),
    sidebarLayout(
        sidebarPanel(
            actionButton("clear", "Clear"),
            downloadButton("save", "Save as PNG")
        ),
        mainPanel(
            plotOutput("plot", click = "plot_click"),
            verbatimTextOutput("info")
        )
    )
)

server <- function(input, output, session) {
    points <- reactiveVal(data.frame(x = numeric(0), y = numeric(0)))

    output$plot <- renderPlot({
        ggplot(points(), aes(x = x, y = y)) +
            geom_path(size = 1, color = "black") +
            theme_minimal() +
            xlim(-10, 10) +
            ylim(-10, 10)
    })

    observeEvent(input$plot_click, {
        new_point <- data.frame(x = input$plot_click$x, y = input$plot_click$y)
        points(rbind(points(), new_point))
    })

    observeEvent(input$clear, {
        points(data.frame(x = numeric(0), y = numeric(0)))
    })

    output$save <- downloadHandler({
        filename = function() { "drawing.png" },
        content = function(file) {
            ggsave(file, plot = output$plot())
        }
    })
}

shinyApp(ui = ui, server = server)