Rendering and image export

[evgenyleushkin]

Dear higlass developers,

I recently encountered problem when using 2d-rectangle domains. I was aiming to make transparent rectangles, however after setting opacity to 0%, a couple of squares retained opaque filling. Zooming in and out can also add additional squares with non-0 opacity. (see the image attached). Additionally, when trying to export png or svg, I always only get empty files.
HiGlass.pdf