---
title: Change the unit of figure size
output: rmarkdown::html_vignette
vignette: >
  %\VignetteIndexEntry{Change the unit of figure size}
  %\VignetteEngine{knitr::rmarkdown}
  %\VignetteEncoding{UTF-8}
---

By default, R Markdown employs inch as a unit of figure size.
You can change it by `hook_figure_unit`.

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

**CAUTIONS**

* This hook must not run twice in a document. Otherwise, you will face unexpected figure size.
* RStudio IDE do not detect the hook and treats `fig.width` and `fig.height` in inches.
* This hook sets `NULL` to the `fig.retina` chunk option.

# Basic usage

`hook_figure_unit()` changes to the unit of figure size to millimeters.
Note that this hook will not change the default size.

```{r setup}
library(chunkhooks)
hook_figure_unit()
```

```{r, fig.width=50, fig.height=50}
# fig.width=50, fig.height=50 (50mm * 50mm)
plot(1)
```

## Other units

You may change default unit by the first argument, `unit`.

```{r, eval=FALSE}
hook_figure_unit("cm")
```

Choices are followings:

```{r}
measurements::conv_unit_options$length
```