---
title: "How to use colored text in Quarto figure captions"
format:
  html:
    toc: true
  pdf:
    toc: true
---
  
In figure captions, it is often useful to say refer to colored objects by printing
the words in their colors.
How can I do this with output in HTML or PDF?

Define a function to colorize text, that can be used in HTML or PDF output

```{r colorize}
# colorize text: use inline as `r colorize(text, color)` to print `text` in a given `color`
# can also be used to color a color name, as in r colorize("red")`
colorize <- function(text, color) {
  if (missing(color)) color <- text
  if (knitr::is_latex_output()) {
    sprintf("\\textcolor{%s}{%s}", color, text)
  } else if (knitr::is_html_output()) {
    sprintf("<span style='color: %s;'>%s</span>", color, text)
  } else text
}
```

In normal text, I can use `colorize()` to
print text in `r colorize("red")`, `r colorize("blue")`, `r colorize("green")`, ... 

But not in a figure caption.

This works but the text is not colored in the caption of @fig-test

````qmd
#| label: fig-test
#| out-width: "70%"
#| fig-cap: Some points should be red, some blue, some green
cols <- c("red", "blue", "green")
plot(1:10, pch=16, cex = 3, col = cols)
````

```{r}
#| label: fig-test
#| out-width: "70%"
#| fig-cap: Some points should be red, some blue, some green
cols <- c("red", "blue", "green")
plot(1:10, pch=16, cex = 3, col = cols)
```

## Inline expression in a caption
`colorize()` doesn't work in a caption. The expression is not evaluated, and just prints in the caption
as a literal, in code font.

````qmd
#| label: fig-test2
#| out-width: "70%"
#| fig-cap: Some points are `r colorize("red")`, some are `r colorize("blue")`, some are `r colorize("green")`
cols <- c("red", "blue", "green")
plot(1:10, pch=16, cex = 3, col = cols)
````

```{r}
#| label: fig-test2
#| out-width: "70%"
#| fig-cap: Some points are `r colorize("red")`, some are `r colorize("blue")`, some are `r colorize("green")`
cols <- c("red", "blue", "green")
plot(1:10, pch=16, cex = 3, col = cols)
```

## Try !expr
One solution: use the YAML `!expr` "tag" literal in `fig-cap`:

````qmd
#| label: fig-test3
#| out-width: "70%"
#| fig-cap: !expr paste("Some points are", colorize('red'), "some are", colorize('blue'), "some are", colorize("green"))
cols <- c("red", "blue", "green")
plot(1:10, pch=16, cex = 3, col = cols)
````


```{r}
#| label: fig-test3
#| out-width: "70%"
#| fig-cap: !expr paste("Some points are", colorize('red'), "some are", colorize('blue'), "some are", colorize("green"))
cols <- c("red", "blue", "green")
plot(1:10, pch=16, cex = 3, col = cols)
```

## Can we simplify this?

Define color names as global variables and use `glue::glue()`
```{r}
red <- colorize('red')
blue <- colorize('blue')
green <- colorize("green")
library(glue)
```

````qmd
#| label: fig-test4
#| out-width: "70%"
#| fig-cap: !expr glue("Some points are ", {red}, " some are ", {blue}, "some are ", {green})
cols <- c("red", "blue", "green")
plot(1:10, pch=16, cex = 3, col = cols)
````
Voila! This is much easier to type in captions, but need to add spaces

```{r}
#| label: fig-test4
#| out-width: "70%"
#| fig-cap: !expr glue("Some points are ", {red}, " some are ", {blue}, " some are ", {green})
plot(1:10, pch=16, cex = 3, col = cols)
```

## Final solution

Use the color name variables, but just use `paste()`

````qmd
#| label: fig-test4
#| out-width: "70%"
#| fig-cap: !expr paste("Some points are", red, "some are", blue, "some are", green)
plot(1:10, pch=16, cex = 3, col = cols)
````