The following fails

library(ggplot2)
library(elementalist)

ggplot(mpg, aes(displ, hwy)) +
  geom_point() +
  theme(axis.ticks = element_line_wiggle(1))
#> Error in xy[-nxy, , drop = FALSE] - xy[-1, , drop = FALSE]: non-numeric argument to binary operator

Most likely because I've been ignoring the existence of compound units, such as arithmetic units (e.g. unit(1, "cm") + unit(0.2, "npc")). I've checked this through the debug system. I don't know what the optimal solution is, but here are some thoughts:

• Delay evaluating line manipulations until draw time. This allows me to convert to absolute units first and then apply manipulations. Downside is that there is no consistency in line manipulations anymore as the plot window is resized and it makes resizing slower.

• If this is an edge case for the axis guide ticks, we could probably get away with solving this in the particular case of axis guides instead of solving the general case. The only other 'ticks'-case I can think of are the guide_colourbar() ticks, but these don't appear to be under the control of the theme system.

• Get advice from someone smarter than me on how this can be solved best.

• Error more gracefully

Should make some geoms that take grob building from the element.

Line elements

• geom_line()
• geom_path()
• geom_segments()

Rectangle elements

• geom_rect()
• geom_tile()
• geom_bar()/geom_col()

Here is a collection of ideas for this package. If you have a good idea for theme elements, feel free to comment.

General Ideas

Shadow

Copy-paste the element at an angle and an offset in a (by default) dark gray colour.

Blur

Either copy the element at varying levels of alpha, or render as raster first, blur the raster, use raster as element.

Rectangle ideas

Image rectangles

An element_rect-class that displays a raster image in the rectangle.

Rounded rectangles

An element_rect-class that will draw rectangles with rounded corners.

Inverted rounded rectangles

An element_rect-class that has quarter-circle 'bites' from the corners

Line ideas

Zigzag

An element_line-class that will show sawtooth/zigzag pattern.

Sine-wave

An element_line-class that will show sine waves.

Ambient noise

An element_line-class that has noise based on the ambient package (simplex, perlin).

Raster lines

An element_line-class that will plot a raster image along a line.

Text ideas

Jiggle

An element_text-class that adds noisy rotation to letters.
Don't even know how to begin with this.