Help required: VRay Dirt with diffuse bitmap texture map

[denyerec]

I'm trying to use the Vray (vray 1.49.01) dirt shader in conjunction with a regular texturemapped surface and am running into difficulties.

First, I create a basic texture mapped surface using a material with a single diffuse component. I set the diffuse colour to type texBitmap and apply my bitmap texture. I use a bumpmap in the material bump channel.

When I render, I now get a lovely brick wall

Now I am confused as to where/how I apply the dirt layer. If I create a new diffuse layer in the material, it obscures my texture map. I kinda need to "overlay" the dirt over the texture mapped surface. In all the example videos I've seen on youtube so far, the dirt shader is always demonstrated on a flat colour surface (EG Here: http://www.youtube.com/watch?v=qYIxij9T7ac ) and I have yet to see an example of the dirt shader being applied over the top of a bitmap texture.

Can anyone offer any pointers on what I'm missing here? I briefly investigated the "blend" shader, but it only allows a % blend rather than a blend-mode option. If blend-mode were present it'd be a simple case of selecting "Darken" and using a dark dirt colour, but I don't see a way to do this.

In summary:

I wish to apply the VRay dirt shader to a bitmap textured wall.

Many thanks!

[thomthom]

I use the dirt map in the transparency slot of the main diffuse layer - the one with the bitmap. Then I have a Black diffuse underneat (or some other dirth-ish texture) The underlying diffuse layer will then shine through.

[valerostudio]

Instead of using the color in the white slot for the DirtMap, just use TexBitmap and choose your brick pattern. In order to get the UV mapping correct, you have to do as Fernando does in this video and place another Diffuse layer above the dirt layer and set its transparency to AColor and choose white. This is the typical workaround for mapping textures that are in the Diffuse slot (and you want to see them visually in SU), so its a good trick to learn.

[thomthom]

I put together a little article on how I use the Dirt map to add details and shading enhancements: http://www.thomthom.net/thoughts/2012/0 ... rtmapping/

[andybot]

I put together a little article on how I use the Dirt map to add details and shading enhancements: http://www.thomthom.net/thoughts/2012/0 ... rtmapping/

Thanks for that! I like the idea of extruding the edges down to control where the dirt effect happens.

[denyerec]

That's brilliant, thankyou all kindly for your help!

[panixia]

thanks tomhtom for the useful "adding edges" trick. you are plain genius.
oh and very thanks for quad face tools. it actually made my life a little bit better!