Fix the background color bug when exporting video with the "random" background option

[KevinXu02]

Set default bg to viser color in gs to fix strange bg color in rendering.

[bobye]

Training with random background is a feature not a bug.

[KevinXu02]

Training with random background is a feature not a bug.

Hi! This modification won’t affect training, the background is still randomly picked. It only changes the background color when exporting video.

[jb-ye]

I see. But the code here is quite confusing. Could you add some comments explaining the effect of setting this to a magic value?

[KevinXu02]

I see. But the code here is quite confusing. Could you add some comments explaining the effect of setting this to a magic value?

Oh, the value is just the same background color as the one for viser. The training background logic is defined seperately, so this value would only work when it is not in training.

[jb-ye]

Yeah, I know. That's what I suggested for adding those comments above the line of change.

[KevinXu02]

Yeah, I know. That's what I suggested for adding those comments above the line of change.

Comments added. Thank you for your suggestion.

[kerrj]

This works as a patch, but what might be a more permanent fix is to propagate the background color set in viser into render crop_data so that this line gets called even if the scene isn't cropped

[kerrj]

fixes #2815 , but might want to revisit how background is handled in the render crop_data so that users can define a background even if the 'crop scene' option is not selected