Paint puddles in Unreal Engine - Tip of the Week

Michał Franczak 2017-05-11 15:27 tutorial  > Unreal Engine  > texturing

Create water puddles, paint strokes and mix different textures and material parameters with vertex painting.


This week we will learn how to use Vertex Painting to make some water puddles on a pavement.

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Fo the purpose of this tip, I created just a simple rectangular box. I tesselated it quite a bit and imported to Substance Painter 2. I wanted some bumpty pavement material so I downloaded Stone with Sidewalk material from Substance Source Library. I exported textures in 2K with two sets: Unreal Engine packed and "Document channels + AO". I needed this second preset, because I wanted to have additional height map, it will be useful later.


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I imported my box to Unreal as FBX. As you can see, the mesh is pretty dense, it will be great for painting, because the strokes will be more precise. It will cost a lot of processing power though, so I recommend to tesselate with moderation - it's a bit of overkill here.


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I plugged textures exported from Substance Painter (Unreal Engine packed set) to new material. I also made small function for controlling tiling of the texture. I used scalar parameter muliplied with TextureCoordinates and put it in each texture UV slot. This way I will be able to change tiling whenever I will want to.


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The water has a different color than bricks, so we need to use color space that varies between pavement texture and a water color. We use LERP for this (just imagine it as a gradient between parameters). We control the mix with our Vertex Color. We just need one channel for that. In this case we use red. To add LERP node, press "L" and left click anywhere on the free space of Material Panel. To add "Vertex color", right click and type "Vertex Color" in a search box.


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We place our LERP function between base color texture and base color sample slot. Now, if we will paint with red color, we will get white color over our pavement. We could use even different texture if we would like to.


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I saved and closed the material and created material instance. The instance is now assigned to a box. And it became completely white. The reason of that is simple - by default, new object has 1 in each vertex color value (which means it's already "full covered with water". We need to erase this color -> let's fill it with 0 value in red channel. What will happen?


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By painting with "0" (black) value in red channel we reveal original color of pavement material.


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We painted all mesh with black in red channel, so now we have our "original state" of the material back.


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The liquid should also have a different roughness than the stone, so we insert another LERP function that will vary between stone roughness and liquid roughness basing on red channel vertex paint. We use 0 as a default value of new parameter.


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As you can see, our white liquid became more glossy / less rough.


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Another LERP goes into Normal slot. We vary between original Normal map that we exported from Substance Painter and a solid 100% blue color from Unreal Engine 3 Vector node. To add this node you need to press "3" and left click anywhere in material panel.


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After saving our material, we get rid of stone bump over liquid.


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Let's change liquid color in material instance.


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Liquid is more blue, but still 100% opaque, we need to fix this.


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First, let's add another LERP in AO slot, so we don't get AO artifacts over our liquid.


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Now, we can import our height map to Unreal, but first we need to tweak it a bit. I used levels to increase contrast of the map. It will be usefull to simulate liquid in the space between stones.


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If we substract our map from Vertex Color we get more liquid in the black areas and less in the white areas. Which means - more liquid in lower areas, pockets and scratches. 


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The result is wet pavement.


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Just for fun, let's crank up the levels and reimport the map.


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The result is much more prominent, but still - we don't have a puddle, only some wet stones.


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First, let's use our UV texture coordinates on this map...


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Now by dividing our "substract" node by scalar parameter and clamping the result between 0 and 1 we can get our liquid offset (LiquidLevel node on the image).


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The result of increased LiquidLevel - much more liquid! And we can bring even more by increasing LiquidLevel value in material instance.


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The final touch: if we multiply our liquid level by scalar parameter, we can change the opacity of the water. We don't want to change roughness, normal or AO values, just the color. So we place Multiply slot between our vertex Painting node group (which ends with Clamp node) and LERP node that controls base color.


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The result is transparent water. We can go further from here with painting  displacement, but it's just a simple tip, so we are ok for now. Have fun!



Author: Michał Franczak Editor: Michał Franczak
Tags: textures water puddle unreal liquid vertexpainting
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