VFX Research

Unreal & Unity, HLSL, C#, C++, Blueprint, Shader graph, Compute shaders...

Realtime world painting

Made with Unreal Engine 4.

2 solutions to paint on a world. The first favors performance and memory, the second has better vertical fidelity.

1st method - heightmap

2nd method - volume texture

How It Works - 1st method

This method uses a heightmap.

The mesh will be rendered as paint if a pixel's world space coordinate is lower than the value of the heightmap.

There are 2 components to this system:

The material

It reads the heightmap from a render target and renders paint where needed.

The compute shader

Writes on the render target. We can't use a material to write on the render target here because materials would add pixel values on top of one another.

It is dispatched by an actor.

Compute shaders are not natively supported by Unreal. I'm using a plugin as a template here.

This method is very efficient : all of the paint information is stored in a 1024x1024 grayscale texture, and read/write operations are handled by the gpu.

How It Works - 2nd method

This method uses a volume texture.

The mesh will be rendered as paint if a pixel's corresponding volume texture pixel is higher than an arbitrary number.

This allows for vertical gaps, and a "spreading" effect by using a gradient brush.

This system uses the 2 same components:

The material

It uses world space coordinates to read the values on the volume texture, and renders as paint if the value is above 0.5.

The compute shader

Writes on a volume render target. Each thread writes the full height (64 pixels).

It is dispatched by an actor.

This method also uses the plugin as a template.

This method is less efficient : the volume texture is 1024x1024x64, and takes up ~80 megabytes of memory. Still, it uses the gpu for parallel computation, therefore not affecting performance that much.

2D obstructed blood splatter generator

Without Collisions

With Collisions

Made with Unity.

An optimised solution to create an animated blood splatter without particles and using the power of the gpu.

The collisions are computed only once.

the blood looks black because of an encoding problem.

How It Works

Place a circular mesh

The shape of the mesh defines the shape of the blood splatter

Compute the collisions, restrain the mesh, recompute the UVs

Generate a blood texture with gradients, apply it to the mesh material

Apply a gradient step shader

Animate the clip threshold

The code

Members of the class

Changing the mesh according to collision data

Blood animation

Clipping/coloration shader

Generating the blood texture

The blood texture is generated procedurally to avoid repetition using a compute shader. It avoids unnecessary computation at runtime.

How It Works

Generate the central splatter

Generate the blood lines

Combine

Fade according to distance

Add noise

Dispatching the shader

Example

In game (work in progress)

Notes

The feature took ~10 hours to develop, including the thinking of the concept and gathering of references.

The system could be further optimized by drawing the final blood texture on a large texture covering the entire level after the animation, to avoid unnecessary shader computations and to remove the vertices from the now inactive splatter of blood.

The noise function was taken from Shadertoy.

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