---
title: "Annotating ggplot2 with SVG"
output: html_document
vignette: >
  %\VignetteIndexEntry{Annotating ggplot2 with SVG}
  %\VignetteEngine{knitr::rmarkdown}
  %\VignetteEncoding{UTF-8}
---

```{r, include = FALSE}
knitr::opts_chunk$set(
  collapse = TRUE,
  comment = "#>",
  fig.height = 5, 
  fig.width = 5
)

#~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
# Ensure that images are rendered using a device which understands patterns
#~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
knitr::opts_chunk$set(dev.args = list(png = list(type = "cairo")))
```

```{r setup}
library(grid)
library(ggplot2)
library(svgparser)
```


## Load SVG from web

Since `{svgparser}` uses `{xml2}`, it can load SVG files from a URL.

Note the linear gradient on the R logo is preserved in the conversion to an 
R grob object.

```{r out.width = "30%", fig.height = 4}
rlogo_url <- 'https://www.r-project.org/logo/Rlogo.svg'
rlogo     <- svgparser::read_svg(rlogo_url)

grid.draw(rlogo)
```


## Add 'grob' to ggplot2 with `annotation_custom()`

```{r fig.height = 4}
ggplot(mtcars) + 
  geom_point(aes(mpg, wt)) +
  annotation_custom(rlogo, xmin = 28, xmax = 33, ymin = 4, ymax = 5) +
  labs(title = "svgparser::read_svg() + ggplot2") + 
  theme_bw()
```