Random flicker with sorted draw calls

[aerys]

Random flicker with sorted draw calls

[JMLX42]

Hello and thank you for your feedback,

creating a copy of the array to sort it instead of resort the original array everytime

Creating a copy of such array at every frame is a really bad idea. We try to avoid memory allocation as much as possible.

changing Sort.flashSort(sortValues, calls, numCalls); with calls.sortOn("depth",Array.NUMERIC|Array.DESCENDING)

Array.sortOn must be something like 100x slower than our implementation of the "flash sort". So it's really not an option either.

when you have sorted draw calls due to alpha blending and some calls happen to have the same depth ( lots of triangles in tight space, I guess ) the sorting method in RenderController.render generates random order for the calls woth equal depth, and the result is flickering.

This situation should happen only on very rare occasions. So it would really be a bad fix to simply wast a lot of memory/time at every frame simply to avoid an issue that is not supposed to happen.

The flickering occurs because the flash sort is not stable: items with the same value will not have the same position after every sort. So the fix is to make the flash sort stable (I'm not sure it's doable) or implement a new sort faster than Array.sortOn but stable.

Regards,

[warrenseine]

The z-fight issues cannot be solved this way. You may, indeed, fix some flickering issue by using a stable sort, but you can't be sure which triangle will appear.

Also, using sortOn could have a negative impact on performance.

[Tortenazor]

I know this is really a bad idea, but I was in a hurry and it fixed the issue for me. I didn't have millions of triangles anyway so I could afford the dirty trick...

[JMLX42]

logged internally as feature #1128: "implement stable sort for draw calls"

I know this is really a bad idea, but I was in a hurry and it fixed the issue for me.

Good thing it's open source in this kind of situations :)