We start on a windows X64 (RGui) system with:
library(igraph)
g <- graph_from_literal(A +-+ B)
plot(g, edge.color=rgb(0,0,0,0.3))
This shows as expected a graph with two vertices connected with an edge.
The next step is to repeat the previous statement with <up arrow> and <return>. Now the edge has disappeared.
The cause is that the first plot statement changed the value par()$xpd = FALSE to TRUE. When saving the graphical image to a PDF file, the edge reappears. In contrast, PNG shows the image as in the R Graphics device, without edge.
Different, but possible related is the following problem:
dev.new()
plot(stack_graph,
layout = layout_in_circle(stack_graph),
vertex.shape = "sphere",
edge.color = rgb(red=0x66/255, green=0x66/255, blue=0x66/255, alpha=0.3), # Transparency issues caused by non valid RBG color code.
edge.arrow.size = 2 # Changing size > 0 will show transparency issues of the graph vertices.
)
After saving this image as a .pdf file, the color of the vertices became transparent.
See: Directed graphs (with arrows) causes vertex color transparency.
The code below shows arrows with different transparencies.
plot(make_tree(5, mode="undirected"), vertex.size=10, edge.arrow.mode=3, edge.color=rgb(0,0,0,0.2))
Are these errors in coding, features or bugs?
And reproducible on platforms other than Windows?