ggplot2: One line of panel.background always gets dropped

[expersso]

library(ggplot2)
library(svglite)

svglite("testplot.svg")
qplot(mtcars$cyl) + theme_bw()
dev.off()

[expersso]

An even more minimal example:

library(ggplot2)
library(svglite)

svglite("testplot.svg")
ggplot(NULL) + theme(text = element_blank(), 
                     axis.ticks = element_blank(),
                     plot.background = element_blank(),
                     panel.background = element_rect(color = "black"),
                     panel.grid = element_blank())
dev.off()

<?xml version='1.0' encoding='UTF-8' ?>
<svg xmlns='http://www.w3.org/2000/svg' xmlns:xlink='http://www.w3.org/1999/xlink' viewBox='0 0 720.00 576.00'>
<defs>
  <style type='text/css'><![CDATA[
    line, polyline, path, rect, circle {
      fill: none;
      stroke: #000000;
      stroke-linecap: round;
      stroke-linejoin: round;
      stroke-miterlimit: 10.00;
    }
  ]]></style>
</defs>
<rect width='100%' height='100%' style='stroke: none; fill: #FFFFFF;'/>
<polyline points='5.48,570.52 5.48,5.48 714.52,5.48 714.52,570.52 ' style='stroke-width: 1.07; fill: #EBEBEB;' />
</svg>

The polyline only draws three of the four sides.

sessionInfo()
R version 3.2.2 (2015-08-14)
Platform: i386-w64-mingw32/i386 (32-bit)
Running under: Windows 7 x64 (build 7601) Service Pack 1

locale:
[1] LC_COLLATE=English_United Kingdom.1252  LC_CTYPE=English_United Kingdom.1252    LC_MONETARY=English_United Kingdom.1252
[4] LC_NUMERIC=C                            LC_TIME=English_United Kingdom.1252    

attached base packages:
[1] stats     graphics  grDevices utils     datasets  methods   base     

other attached packages:
[1] gdtools_0.0.4      svglite_1.0.0      ggplot2_1.0.1.9003

loaded via a namespace (and not attached):
[1] labeling_0.3     colorspace_1.2-6 scales_0.3.0     plyr_1.8.3       tools_3.2.2      gtable_0.1.2     Rcpp_0.12.2     
[8] grid_3.2.2       munsell_0.4.2   

[yixuan]

I think I figured out the cause of the problem.

The reason why one line was dropped off is that the current svglite does not support clipping, so R will calculate the boundary of the plot and remove elements that are outside of it. Due to some rounding errors one or more border lines get a chance to be removed.

If we do not provide our own clip() device function, there seems to be no way to avoid it.

[hadley]

@yixuan clipping shouldn't be too hard to implement, right? We can just continue to draw everything, but put it in an element that clips? (Hmmmm, after reading the svg docs a bit this might be hard because we need to declare a <clipPath> at the top of the doc)

[yixuan]

It seems possible to implement a clip() device function in svglite: https://developer.mozilla.org/en-US/docs/Web/SVG/Tutorial/Clipping_and_masking, with the price that each element will gain another attribute clip-path.

[yixuan]

I believe we can define multiple <clipPath> in the body of SVG and assign each one an ID. Then the following elements just need to refer to the proper clip path.

[hadley]

Oh I see you can define it just before you use it:

<g clip-rule="nonzero">
  <clipPath id="MyClip">
    <path d="..." clip-rule="evenodd" />
  </clipPath>
  <rect clip-path="url(#MyClip)" ... />
</g>

[yixuan]

Yep. I could try to make a PR today to implement this.

[hadley]

That would be awesome - I want to aim for a release around Feb 12