Choppy Rendering of Graph

shiny
1

Hi All,
I am an intermediate R user, completely new to shiny and web development.

I wanted to create a simple ap that highlights a particular point on a plot based on a slider value. I'd like the highlighted point to SMOOTHLY vary as you change the slider.

My first attempt is here:
https://guptavis.shinyapps.io/choppyslider/

The app is "choppy," i.e. there seems to be a noticeable lag after you release the slider for shiny to re-render the plot. I wanted something with smoother handling that updates AS you move the slider, like this:
http://bl.ocks.org/pranitar/01305d9ad0eba73dbf80

Any suggestions, please? I'm happy to move to ggvis or another graphing application if it would fix the problem?

Code:
server.R

library(tidyverse)
library(ggplot2)
library(shiny)

#Defined outside reactive elements for efficiency
x_grid <- seq(from=-2.2, to=2.2, length.out=100)
base_plot <- tibble(x = x_grid, 
              pdf = pnorm(x_grid)) %>%
              ggplot(aes(x,pdf)) + 
                  geom_point() + geom_line()

# Use slider to highlight particular poitn on plot
shinyServer(function(input, output) {
    output$distPlot <- renderPlot({
    
    x_val = input$x
    base_plot  + geom_point(x=x_val, y=pnorm(x_val), 
                           color="pink", size=10) + 
                  geom_vline(xintercept = x_val, color="blue")
      })  
})

ui.R

library(shiny)

shinyUI(fluidPage(
  
  titlePanel("Choppy Re-Rendering"),
  
  sidebarLayout(
    sidebarPanel(
       sliderInput("x",
                   "X-Value",
                   min = -2,
                   max = 2,
                   value = .1, 
                   step = .1)
    ),
    
    mainPanel(
       plotOutput("distPlot")
    )
  )
))