... it wasn't the excited, playfully gamboling gamma rays from a heretofore unnoticed pulsar playing patticake with the upper atmosphere and causing concussive bangs to reverberate all over the world. It was just me thudding my head into a wall
I had been doing a render. In fact for quite some time. I had started it off and at 23% it ran into a 'road-block' - at which point i went to bed, hoping/assuming that it would clear by the time I arose (notice I cunningly did not say 'in the morning ...' ) Well, I arose and ... it was still at 23%. Examination of the area of the render identified what was probably the issue. Just a small area all things considered so I let it go. Many hours later it was still at 23%. So I cancelled the render.
The area in question was a vulture and I seemed to recall having issues with the transmaps and ray-trace shadows with those before. I retextured the bird as it was quite uniform and pale, and then selected the 'obvious candidates' of the various ruff and feather surfaces and set them to UberSurface so I could turn off raytrace and occlusion on them.
Kicked off the render and all seemed good, the render of the bird started to appear so, I let it run.
A fair bit later I re-checked progress and it was at 53%. A later check showed it was at 53% still. Another road-block? Examination showed it to be ivy against a building. I pondered. Did I cancel it again and reset the shader? Generally vegetation does not cause that much of an issue - yes it can stall things a bit, but generally to an acceptable degree. So I let it run. And run. And run. It staggered and staggered, slowly, oh so slowly ticking over to 54%, then 55%.
Eventually after a terrible amount of render time it had managed to get to 69%. I really, really and truly should have cancelled, re-shadered and restarted the render. If you ever wonder "should I ...?" The answer is "YES! Do it. Do it NOW!"
It gets to the stage where you don't want to cancel things mainly because of all the time you have invested in it. Not to mention probably enough electricity to boil enough water to make enough apple tea to keep the crew of a battleship scurvy-free on their journey from here to Alpha Proxima and back - assuming four hour shifts at the oars ...
Finally I noticed the sound of the CPU fan wind down. Yay! All done? yes, sort of. It had wound down as I had managed to 'nerf' the power cord of the laptop just enough to unplug it but not enough to make the lead fall out. So it had powered off. Losing what had gone before. I really, really should have cancelled the render hours (days, in fact!) before and got it sorted out.
I really and truly should try out much, much smaller test renders to see if there are any waiting gremlins. I still cannot believe just what an effect the plumage on the vulture and the ivy against the wall had on render times. We learn by our mistakes! Maybe this lesson will stick, this time