Blackmagic Forum

so I'm working with a 3d particle emitter in a 3d solved scene in order to make rain. Pretty standard stuff of a 3d solved camera that's been exported into a scene with Camera3d, Merge3d, CameraTrackerRender.

So I have my rain particle made and it's being connected to the merge3d node and looks fine but, I cannot figure out how to adjust the blend mode of the particle to complete the rain look.

My only work around so far has been to replace the 3d scene input with a background node, turn on it's alpha and then do the final composite with a merge node after the CameraTrackerRender to put my particles back over top of the original footage. This works but, I dont really like it and I feel like Im missing something obvious in the particle emitter / render somewhere to just adjust the blend mode.

I thought about an image plane node after the P-render but, this just introduced more problems than it solved.

I probably would’ve used a simple merge with the normal blending modes available.
If you absolutely need to to this in 3D then you can use an override3d and set a blending mode there.

When using the software renderer you should have all blending modes from the merge available. But in OpenGL you will miss out on a few.

UserNoah wrote:I probably would’ve used a simple merge with the normal blending modes available.
If you absolutely need to to this in 3D then you can use an override3d and set a blending mode there.

When using the software renderer you should have all blending modes from the merge available. But in OpenGL you will miss out on a few.

So the problem is that 2Dmerge cant be used with a 3D particle until it's been flattened down by a camera renderer and the 3Dmerge node doesn't have any blend options, it just passes through things like image planes (that do have blend modes) provided you set the camera renderer to software as you pointed out.

I didn't know about 3d override node so I'll give that a look.

Update, just tried sending a 2d particle to an image plane to use in a 3d scene. This resulted in some very strange behavior of the particle and the blend modes. I was able to fix this by sending the particle to a merge node with an alpha BG then into the image plane. But, this still didn't return the best results for blend modes through the image plane options.

I cant stop thinking about how bad this problem actually is!

Okay imagine you have a 3D scene and including a background and particles you have 5 elements that need to be composited together. so a background plate, an actor keyed on green, a 3d modeled prop with textures and lighting, and some other foreground element like leaves of a tree you roto'ed and just have as a simple image plane, and finally a particle effect like rain. And because this is a scene with visual depth and because you're working in 3d you decide to use a 3D particle for your rain so that way you will have rain in front of and going behind all elements. Oh and your camera has a move and pan to but your solve on it is like .2 accurate so that's awesome.

okay so let me jump to where this all hits a horrible wall, the particles!

First good points about working this way with particles, all of your particles are held out or masked correctly by the elements in the scene, they have true depth so when you camera pans and moves their perspective shift is great looking. It's also easy to adjust the look of the particle* by viewing the 3d scene render output while you work on the pEmitter settings.

Now the bad, because you're working with 3D particles you cant use any particle blur, glow, or blend mode so there goes 95% of your compositing tools. But no worries... there's a work around...

All you have to do is copy over your entire 3D scene and most of its working inputs (like your actor on green screen) and then replace everything with black. So on your Camera's scene input where you had your background footage, replace that with a background node node now and set it to black 0.0.0. color. For your actor's footage add a Brightness contrast node, crush it to black and then clip the black and white values on it. For your 3D modeled prop with textures, replace all of those with flat black values, and then for your tree leaves roto replace with black too.

Great now you have your whole scene built again with all flat black objects and your particles around them. Now after your 3d Scene render node what you'll want to do is add any blur or glow you want to your particles. After those nodes now extract an alpha from all that black with particles on it and composite the whole thing back over your original 3d scene output with a 2d merge node and finally adjust the blend to your liking...

okay maybe not so bad... Until you realize that if you want to change anything in your original 3d scene, like maybe you decide the actor on green screen needs to be moved a foot to the right, or actually his layer needs animated a little bit so that he starts and ends the scene in the correct position...
Well now you have to go and copy those changes over to your 3d particle scene environment where you have all of these black hold out materials...

Of course everyone's workflow is different, but a lot of people don't want to put their greenscreen cutout rendered and composited all in one go. Almost every tutorial on greenscreen will spend a lot of time on how to massage the edges, add lightwrap, match the colors etc. This all happens in the 2D part of the equation. What you're describing when you want to change stuff around is easily done by for example copying and instancing nodes, so you'll get a synced 3D setup where if you change one thing you change the other as well. This is a pretty common way of working as well.

Sander de Regt wrote:Of course everyone's workflow is different, but a lot of people don't want to put their greenscreen cutout rendered and composited all in one go. Almost every tutorial on greenscreen will spend a lot of time on how to massage the edges, add lightwrap, match the colors etc. This all happens in the 2D part of the equation. What you're describing when you want to change stuff around is easily done by for example copying and instancing nodes, so you'll get a synced 3D setup where if you change one thing you change the other as well. This is a pretty common way of working as well.

I mean, just because I simplified my example by saying green screen doesn't mean I'm not talking about a 20 node structure that does everything you mentioned and then goes onto a 3d image plane and into a scene. I mean soon as you start talking about a 3D scene with all of the elements I mentioned (Cameras, BGs, FGs, and particles) you really need to be able to composite them all in the same environment for the best look. Otherwise, if you're like "baking" a green screen shot and rending it out with an alpha and then bring it back into the comp... Well now you're in an even worse area than with After Effects and precomps...

I did not know about this copy and instance nodes though so thank you for that. Do you know if there a good place I can learn about that feature?

Why do you need to pre-render anything? Assuming you have enough RAM, you can do all of the elements interactively in the same comp.

You can, for example, render out depth slices from 3D and composite them back together in 3D.

Are you using Fusion Studio? I have a particle blur plugin that might help, too. Basically, it blurs the map applied to facing particles and the amount of the blur can be varied based on the distance to the camera. For rain/snow/embers/smoke it works well.

You also don’t have to retexture everything. The override 3D also features a matte mode. So you just combine everything you need to use as a matte in a merge 3D and then use the override 3D and set it to Do Matte (I believe that’s what it’s called I’m not on my computer right now). After that you merge in your particles and still have everything cut out nicely but don’t have to update or calculate two node branches. Much faster and easier to handle.

Then you can render your particles and merge them back in 2D on your scene

Edit: you still end up with two node branches but only at the 3D part. You don’t have to recreate the actor with a background node or create a black texture for the 3D object. Just place the override 3D

UserNoah wrote:You also don’t have to retexture everything. The override 3D also features a matte mode. So you just combine everything you need to use as a matte in a merge 3D and then use the override 3D and set it to Do Matte (I believe that’s what it’s called I’m not on my computer right now). After that you merge in your particles and still have everything cut out nicely but don’t have to update or calculate two node branches. Much faster and easier to handle.

Then you can render your particles and merge them back in 2D on your scene

Edit: you still end up with two node branches but only at the 3D part. You don’t have to recreate the actor with a background node or create a black texture for the 3D object. Just place the override 3D

Oh nice! I'll have to give that a try the next time I run into this problem.

Chad Capeland wrote:Why do you need to pre-render anything? Assuming you have enough RAM, you can do all of the elements interactively in the same comp.

You can, for example, render out depth slices from 3D and composite them back together in 3D.

Are you using Fusion Studio? I have a particle blur plugin that might help, too. Basically, it blurs the map applied to facing particles and the amount of the blur can be varied based on the distance to the camera. For rain/snow/embers/smoke it works well.

No, Im using resolve / fusion studio atm because I was hired to do all the VFX, compositing, and color grading on the film so it seemed like a great chance to put Resolve through the paces and do everything there. Is that plug-in on reactor? it sounds very useful!