v19.0p prog. render issues

[R Reynolds]

I've discovered a progressive render issue in v19.0p. While it's not a show stopper it's been annoying me for a long time and I've finally found the root cause.

This image is an overview of the test chor. There's a camera with a 1000mm lens looking at five instances of a grey reference sphere, each at a different distance from the camera. The sphere instances are scaled in the chor as they get closer to the camera so that from the camera view they don't change too much in image size. They are positioned so the camera can see all five spheres side by side. Between the camera and the closest sphere is a slightly tinted, four patch plane that is a "glass sheet" with a transparency of 80%. It is positioned so that the camera only sees the lower half of the spheres through it. A simple sun light shines down from above and the chor has global ambience turned on with a white colour; intensity = 80% and occlusion = 100%.

 

This image is the results of 5 pass prog renders and 9 pass full screen renders. The first two sphere rows are with no glass in the way while the last two rows have the glass turned on.

For prog. renders through a transparent surface something strange happens as the surface gets farther from the camera. If you turn off ambience and leave in the glass slide this issue also goes away.

Although it always happens in progressive renders, I have seen it occasionally in 9 pass full screen renders of an 80Mb project chor. So if Stefan does try to fix this issue he may want to look at both types of screen rendering.

amb_occl_thru_glass_distant_embed.prj