Note: This tutorial modifies the default_explosion.efx file. This may effect rocket launchers or something else in your map that uses this same effect. It won't cause them not to work, but it will also remove the marks that those weapons make on the surfaces also.
1) Open up your grenade file (stielhandgranate) in a text editor (such as Notepad++). Search for impactType and change the word after it to be none. That part will now look like
Now search for projExplosionEffect add "explosions/default_explosion" after the backslash. This part should now look like
And finally search for projExplosionSound and add "shell_explode_default" after the backslash. This part should now look like
Now save the grenade file and close it.
2) Now open Effects Editor from the Launcher.
Click File>Open and then open the explosion that you used in the first step. For this tutorial I am using "default_explosion". So open up the file in raw>fx>explosions>default_explosion.efx
On the list at the bottom of the window, select the one named decal and then click Edit>Delete.
If you would like to modify the effect in any way you can do that here also.
Now save the effect and close Effects Editor.
3) Open the soundaliases folder in the raw folder. Create a new file named grenade_explosion.csv. Open this file in a text editor and paste the code below into the file.
Now you can save and close this file.
name,platform,file,sequence,vol_min,vol_max,dist_min,dist_max,limit_count,limit_type,entity_limit_count,entity_limit_type,bus,volume_min_falloff_curve,volumefalloffcurve,reverb_send,dist_reverb_max,reverb_min_falloff_curve,reverb_falloff_curve,pitch_min,pitch_max,randomize_type,spatialized,type,probability,loop,masterslave,loadspec,subtitle,compression,secondaryaliasname,chainaliasname,startdelay,speakermap,lfe percentage,center percentage,envelop_min,envelop_max,envelop percentage,occlusion_level,occlusion_wet_dry,real_delay,distance_lpf,move_type,move_time,min_priority,max_priority,min_priority_threshold,max_priority_threshold,doppler,isbig
4) Go back to Launcher and open the Mod Builder tab. Paste the code below into the mod.csv box.
5) You are done! Just rebuild your mod and you should be good to go. You will no longer have any marks on your map from the grenade explosions.
Unfortunately there are so many different problems that can cause this tutorial not to work or behave differently than it did for me. I probably won't be able to help everyone but hopefully this led you in the right direction.
As I was trying to figure out how to do this myself I learned a lot of random things that I couldn't find explanations for. So below I'm going to put a few random things that I learned while doing this. It may help someone.
-The impactType of the grenade not only dictates the impact but also the explosion effect and the sounds to go along with it. If you just set impactType to none then your grenade will still work but everything about it will be completely invisible.
-I don't know if this is just with me, but the UGX WeaponsEditor++ wouldn't save the grenade file for me. And when it did look like it saved, I would open it back up and it would be the same as when I started.
-If you are making a custom texture you can set it to have noMarks in the Asset Manager but when I did that, 1/100 times that I would load the map that texture wouldn't load and appear white. noMarks did successfully make the grenades not make marks, but it had the side effect of sometimes not loading the texture.