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Bloody decals

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    Bloody decals

    Hello again,

    I did a search, but could not find an answer to my satisfaction. I was wondering if you folks have any good links for decals? specifically decals with a lot of translucency.

    My group is in the process of creating evisceration in UDK, we'd like the game to spawn blood decals upon a limb or head detachement which will be done through coding, but I am unclear how to create a blood decal that is partly translucent and, you know. Looks like blood.

    I am familiar with the materials editor, but not enough to have an idea of how to do this.

    Thanks for your time,


    Maybe try at
    There are a lot of good textures. Decals too, but not blood.
    You can try make it by 2D Software (like free GIMP, there are tutorials for it).

    I hope I help you.

    PS: Maybe is here some mistakes, english is not my native language, but you should understand.


      Hi ALthar,

      Thanks for taking the time to reply, I apologize I was not clear in my original post, I know how to create blood, I do not know how to make it look transluscent in the UDK materials editor.


        I have blood decals. They look like this
        Technically placeholder assets, but they work pretty well.


          Hey Max,

          Those are exactly what I'd like to create, Can you give me a quick step by step through Pshop? I im a little unclear on how to create the alpha channel in regards to what goes white what goes black.

          Also, have you had any luck with getting decals to appear on anything other than bsp? Our game is featuring a lot of aesthetic destruction, so, I have a lot of static mesh, fractured mesh and Phys X in the game. I'd love it if I could get decals to appear at least on some of them.

          I look forward to your reply as that is exactly what I was envisioning for blood decals.




            Well, you caught me at a good time with an easy question about something I do all the time...

            First of all:

            I'm a big fan of using decals all over the place. They are extremely useful for adding detail and blending objects quickly. That said, there's three optimizations you should be aware of;

            1. Avoid putting decals on decals. This is one of those things that starts multiplying draw calls, and has the potential of being super expensive.

            2. For everything else in your level, it's very important that anything that should NOT have decals on it does NOT receive them. Just because you can't see them rendering on something doesn't mean it isn't (for example, an alphaed out area of a decal doesn't render anything). So check things like sky, light beams, etc. that you don't intend to EVER have decals and turn off decals for all of them. Also, as your optimizing, you can do the same for everything that doesn't have a decal on it. That's a simple check box:
            In StaticMesh Properties > Static Mesh Component > Rendering > Accepts Static Decals. There's also Dynamic Decals, and plenty of other optimziations you could hit while you're in there (like not casting shadows for objects that are always in shadows).

            3. In the DecalActor Properties > Rendering > Max Draw Distance. You can set this distance so that if you can't see it, it's not rendering. This type of optimization is useful for everything in a level. For decals, because they don't change the shape of anything like static meshes, they can fade out even sooner.

            The texture itself isn't anything special. I used a splatter brush, and clicked a few times using photoshop's default red swatches (for brighter and darker reds). Brushes are real easy to make yourself, which I suggest for very unique work, but they can be Googled and downloaded by the thousands.

            As for alpha channel, as you should had you looked at my material setup, there isn't one.

            This particular blood decal is meant to be a STAIN. By that I mean, it's color information darkens the surfaces it's applied (multiply), same as spilling just about anything on a surface that would leave a stain. Whereas a decal of a manhole cover you'd put in a street would be setup differently. Setting that up is pretty much the same as any material, so you have access to all those features.

            I have no problems with decals rendering on static meshes. As far as I know, neither static nor dynamic decals render on dynamic objects. As a test, I just applied both to an inerpt and a physics object, and neither appeared to render.


              Hey Max,

              Thanks for taking the time, it's really appreciated. I noticed you didn't have opacity hooked up in the material editor, I dunno why I just assumed a blood decal would have an opacity to it, but I think it will save us a lot of time and tweaking if I just make it a stain like you did.

              Those pointers about optimization will come in handy for sure. We'll do a pass of the game and this stuff has been added to the optimization pass list.

              Many thanks again.


                Looks like his technique works fine and is probably faster than having to figure out the alpha channel.

                But, just in case you ever need to work with alphas, I'll explain how they work in UDK.
                I can't help with PS... I barely know how to select colors with the magic wand. :P

                In UDK, there are two Opacity input nodes. Opacity Mask and Opacity.
                You'll only need one of these channels. Which one depends upon your blend mode set in the material.

                Connect your Alpha to Opacity Mask. The black areas will be clear. The white areas will be opaque. You can set the Opacity Mask Clip Value to decide how dark something has to be before it becomes clear. The default is 0.3333. So, any gray in your alpha mask that is less than 0.3333 will be clear. Everything above it is opaque.

                Connect your Alpha to Opacity. Any pure (1.0) white will be opaque. Anything else will be varying amounts of transparent. The darker the pixel, the more transparent. 0.0 will be entirely clear.

                Don't use an Opacity input. The color values in your diffuse are added to the background color. This works well for tinting or staining. Any color will be added to the color behind it so that detail can be seen from both layers. Any diffuse value of 0.0, 0.0, 0.0(RGB) will make no change. 0.0+X=X

                Much like Blend_Additive except that it multiplies the colors. So 1.0, 1.0, 1.0(RGB), also known as white, would be clear. 1.0*X=X

                The other BLEND modes have their uses too, but they are a bit more specialized.

                You can read more about them here:

                In general, Black becomes clear. White is opaque... Unless you're multiplying.



                  Great info. sounds like blend transluscent is the route I need to go if I start creating the water and blood decals I was originally picturing.