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I'm trying to draw previous frame of animation on screen

you can see this effect here: https://youtu.be/WNL_KJNl6pU

Mortal Combat X (left) , Street Fighter Alpha 2 (right):

Johnny slides in to land a hit, leaving behind a glowing green trail that looks like multiple instances of himself Cammy jumps up to kick, and leaves behind previous visible ghosts of herself

This effect also found in animation software and called onion skinning:

a deer's gallop

I've implemented this by spawning object every second but I think It is possible with shader.

Update

I could make this effect by using RenderTexture for capturing previous frame , but I can't remove background color :(

I tried with Blending and grab pass but don't work(it was rendered normally)!!

sources :

https://github.com/smkplus/TrailingFX

https://unitylist.com/r/4tp/unity-fluid-2d-blur-image-effect

several dozen 3D models in a trailing line

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    \$\begingroup\$ Possible duplicate of Create a trailing, ghosting effect of a sprite \$\endgroup\$
    – John Hamilton
    Commented May 5, 2017 at 9:19
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    \$\begingroup\$ Have you looked into object pooling to avoid the performance hit of repeatedly spawning copies in your trail? \$\endgroup\$
    – DMGregory ♦
    Commented May 5, 2017 at 10:13
  • \$\begingroup\$ Can you confirm this is for 3d? I think that would make it different enough from the suggested duplicate to keep it open. \$\endgroup\$
    – House
    Commented May 9, 2017 at 11:53
  • \$\begingroup\$ @Byte56 yeah I actually work on 3d games.my question is for 3d and isn't duplicate.sorry why my question is close?!?! which questions is close? \$\endgroup\$
    – Seyed Morteza Kamali
    Commented May 9, 2017 at 18:07
  • \$\begingroup\$ It's not closed, there was a vote in progress to close this question as a duplicate of the 2D specific question linked above. \$\endgroup\$
    – House
    Commented May 10, 2017 at 7:25

1 Answer 1

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I would solve this using post processing. You find some way to mask out your ghosting objects (stencil buffer, render layers, w/e) then create a compositing PP effect that combines the current render with the previous renders at a lower opacity. Since you're just pasting new information on top of the old render, you can stack all the previous renders in one texture. This is essentially onion skinning.

You would control how many "ghosts" get displayed based on how quickly you decrease your opacity.

The quick proof of concept I made looks like this (they already faded before I got the screenshot) enter image description here

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  • \$\begingroup\$ how can I combine current render with the previous renders?!?! I'm new to shader please write onion skinning shader in your answer.thanks \$\endgroup\$
    – Seyed Morteza Kamali
    Commented May 5, 2017 at 18:47
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    \$\begingroup\$ Note that this solution is limited to a fixed camera position. If the camera is also moving, this won't work as expected. And @smkplus Don't expect all the work to be done for you, you'll need to make an effort. \$\endgroup\$
    – House
    Commented May 10, 2017 at 7:27
  • \$\begingroup\$ @SeyedMortezaKamali Did you come up with a proper solution for saving previous renders yet? \$\endgroup\$
    – Marten Zander
    Commented Nov 5, 2019 at 16:21
  • \$\begingroup\$ @MartenZander what games do you want to make? there are two solution for trailing ghost effect gh 1.RenderTexture 2.Object pooling \$\endgroup\$
    – Seyed Morteza Kamali
    Commented Nov 5, 2019 at 17:26
  • \$\begingroup\$ @SeyedMortezaKamali actually it's not a game I am working on. it's a demonstrator app, using a static camera. So I guess I would go for the RenderTexture way. \$\endgroup\$
    – Marten Zander
    Commented Nov 5, 2019 at 20:01

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