Drawing is slow when zoomed in on large genes #720
Description
I was trying out Apollo with a lungfish genome that has some really long genes. The longest in the GFF3 is over 17Mbp long (this gene). For reference, the longest human gene is about 2.4Mbp.
I noticed when zoomed in on these long genes that the app is really slow, and traced it back to canvas drawing commands. I think it's probably due to trying to draw the intron directional arrows, but in general the Apollo track draws the whole gene even if it is outside the visible bounds. It hasn't been a performance issue before, but definitely is with genomes like this. The Apollo track should probably limit its drawing commands to the visible area (plus a bit of a buffer area, maybe?).