
# webshot

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**Webshot** makes it easy to take screenshots of web pages from R. It
can also:

- Run Shiny applications locally and take screenshots of the
  application.
- Render R Markdown documents and take screenshots of the document.
  Webshot can handle both static Rmd documents and interactive ones
  (those with `runtime: shiny`).

See the [introduction
article](https://wch.github.io/webshot/articles/intro.html) for examples
in addition to the ones below.

## Installation

Webshot can be installed from CRAN. Webshot also requires the external
program [PhantomJS](https://phantomjs.org/). You may either download
PhantomJS from its website, or use the function
`webshot::install_phantomjs()` to install it automatically.

``` r
install.packages("webshot")
webshot::install_phantomjs()
```

## Usage

By default, `webshot` will use a 992x744 pixel viewport (a virtual
browser window) and take a screenshot of the entire page, even the
portion outside the viewport.

``` r
library(webshot)
webshot("https://www.r-project.org/", "r.png")
webshot("https://www.r-project.org/", "r.pdf") # Can also output to PDF
```

You can clip it to just the viewport region:

``` r
webshot("https://www.r-project.org/", "r-viewport.png", cliprect = "viewport")
```

You can also get screenshots of a portion of a web page using CSS
selectors. If there are multiple matches for the CSS selector, it will
use the first match.

``` r
webshot("https://www.r-project.org/", "r-sidebar.png", selector = ".sidebar")
```

If you supply multiple CSS selectors, it will take a screenshot
containing all of the selected items.

``` r
webshot("https://www.r-project.org/", "r-selectors.png",
        selector = c("#getting-started", "#news"))
```

The clipping rectangle can be expanded to capture some area outside the
selected items:

``` r
webshot("https://www.r-project.org/", "r-expand.png",
        selector = "#getting-started",
        expand = c(40, 20, 40, 20))
```

You can take higher-resolution screenshots with the `zoom` option. This
isn’t exactly the same as taking a screenshot with a HiDPI (“Retina”)
device: it is like increasing the zoom to 200% in a desktop browser and
doubling the height and width of the browser window. This differs from
using a HiDPI device because some web pages load different,
higher-resolution images when they know they will be displayed on a
HiDPI device (but using zoom will not report that there is a HiDPI
device).

``` r
webshot("https://www.r-project.org/", "r-sidebar-zoom.png",
        selector = ".sidebar", zoom = 2)
```

### Vectorization

All parameters of function `webshot`. That means that multiple
screenshots can be taken with a single command. When taking a lot of
screenshots, vectorization can divide by 5 the execution time.

``` r
# Take a screenshot of different sites
webshot(c("https://www.r-project.org/", "https://github.com/wch/webshot"),
        file = c("r.png", "webshot.png"))

# Save screenshots of the same site in different formats
webshot("https://www.r-project.org/", file = c("r.png", "r.pdf"))

# Take screenshots of different sections of the same site.
# Note that unlike arguments "url" and "file", a list is required to specify
# multiple selectors. This is also the case for arguments "cliprect" and
# "expand"
webshot("http://rstudio.github.io/leaflet/",
        file = c("leaflet_features.png", "leaflet_install.png"),
        selector = list("#features", "#installation"))
```

### Screenshots of Shiny applications

The `appshot()` function will run a Shiny app locally in a separate R
process, and take a screenshot of it. After taking the screenshot, it
will kill the R process that is running the Shiny app.

``` r
# Get the directory of one of the Shiny examples
appdir <- system.file("examples", "01_hello", package="shiny")
appshot(appdir, "01_hello.png")
```

### Screenshots of R Markdown documents

The `rmdshot()` function takes screenshots of R Markdown documents. For
static R Markdown documents, it renders them to HTML in a temporary
directory (using `rmarkdown::render()`)and then takes a screenshot.

For dynamic R Markdown documents, it runs them using `rmarkdown::run()`
in a separate R process and then takes a screenshot. After taking the
screenshot, it will kill the R process that is running the document.

``` r
rmdshot("document.rmd", "document.png")
```

### Manipulating images

If you have GraphicsMagick (recommended) or ImageMagick installed, you
can pass the result to `resize()` to resize the image after taking the
screenshot. This can take any valid ImageMagick geometry specifictaion,
like `"75%"`, or `"400x"` (for an image 400 pixels wide). However, you
may get different (and often better) results by using the `zoom` option:
the fonts and graphical elements will render more sharply. However,
compared to simply resizing, zooming out may result in slightly
different positioning of text and layout elements.

You can also call `shrink()`, which runs
[OptiPNG](https://optipng.sourceforge.net/) to shrink the PNG file
losslessly.

``` r
webshot("https://www.r-project.org/", "r-small-resized.png") %>%
  resize("75%") %>%
  shrink()

# Using zoom instead of resize()
webshot("https://www.r-project.org/", "r-small-zoomed.png", zoom = 0.75) %>%
  shrink()

# Can specify pixel dimensions for resize()
webshot("https://www.r-project.org/", "r-small.png") %>%
  resize("400x") %>%
  shrink()
```

To illustrate the difference between `resize()` and `zoom`, here is an
image with `resize("50%")`:

![](man/figures/r-small-resized.png)

And here is one with `zoom = 0.5`. If you look closely, you’ll see that
the text and graphics are sharper. You’ll also see that the bullet
points and text are positioned slightly differently:

![](man/figures/r-small-zoomed.png)
