inconsistency of color's alpha in plot and legend for geom_ribbon and geom_rect

[ptoche]

I have struggled to use transparent colors with geom_rect and geom_ribbon. I haven't been able to find a consistent way to get the legend colors match the fill color in the plot. I haven't measured the inconsistency though, it's based on my visual impression, but let me know if you notice the problem too. My workaround has been to tweak the value of alpha with override.aes inside guide_legend, but it's not ideal. Is there a better workaround?

In the plot below, something between guides(fill = guide_legend(override.aes = list(alpha = 0.1))) and guides(fill = guide_legend(override.aes = list(alpha = 0.2))) seems to give a better result. Am I seeing this properly?

Note that below I have used adjustcolor() function, but the same problem is the same if I use "#FF000080" and "#0000FF80", which are obtained from blue and red by setting an alpha to 0.5. I checked online that the hex values are correct.

library(ggplot2)
ggplot() + theme_bw() +
    geom_ribbon(aes(x = 0:5, ymin = 5, ymax = 0, fill = "red")) +
    geom_ribbon(aes(x = 5:10, ymin = 5, ymax = 10, fill = "red")) +
    geom_ribbon(aes(x = 0:5, ymin = 5, ymax = 10, fill = "blue")) +
    geom_ribbon(aes(x = 5:10, ymin = 0, ymax = 5, fill = "blue")) +
    scale_fill_manual(name = NULL, 
        values = adjustcolor(c("red", "blue"), alpha.f = 0.5)) +
    guides(fill = guide_legend(override.aes = list(alpha = 0.5))) 

Created on 2018-04-21 by the reprex package (v0.2.0).

[hadley]

Every layer gets an entry in the legend, so you need to turn some off:

library(ggplot2)
ggplot() + theme_bw() +
    geom_ribbon(aes(x = 0:5, ymin = 5, ymax = 0, fill = "red")) +
    geom_ribbon(aes(x = 5:10, ymin = 5, ymax = 10, fill = "red"), show.legend = FALSE) +
    geom_ribbon(aes(x = 0:5, ymin = 5, ymax = 10, fill = "blue"), show.legend = FALSE) +
    geom_ribbon(aes(x = 5:10, ymin = 0, ymax = 5, fill = "blue"), show.legend = FALSE) +
    scale_fill_manual(name = NULL, 
        values = adjustcolor(c("red", "blue"), alpha.f = 0.5)) +
    guides(fill = guide_legend(override.aes = list(alpha = 0.5))) 

[ptoche]

I get it thanks!

[ZelinC]

Hello, I am new to geom_ribbon, just a little bit confused with your code and the output graph.
I read this code
geom_ribbon(aes(x = 0:5, ymin = 5, ymax = 0, fill = "red"))
as fill area (0:5, 5:0) red, but it is blue in your plot?
Could you explain why? Many thanks!!

[ptoche]

Try with the fill outside the aes(): geom_ribbon(aes(x = 0:5, ymin = 5, ymax = 0), fill = "red").

Play around with color and fill and compare inside the aes() versus outside!

[lock]

This old issue has been automatically locked. If you believe you have found a related problem, please file a new issue (with reprex) and link to this issue. https://reprex.tidyverse.org/