This technique also estimate how close we are to any nearby geometry. It’s immediately obvious that the flat geometry that faces the camera can be identified immediately. To better understand how it works, we replaced the surface rendering with a colour gradient that indicates how many steps were requires for raymarch to hit a piece of geometry: This brings us to the the distance-aided implementation of raymarching:įloat distance = sphereDistance(position) In such a way we can dramatically reduce the number of steps required to hit a volume. Each ray travels for as long as its distance from the closest object. The following image (from Distance Estimated 3D Fractals) show how raymarch works. What sphereDistance allows us is to have a conservative estimation of how far our ray can travel without hitting a sphere. Without any proper shading, volumetric rendering is fairly uninteresting. Even if this example might seem trivial with a single sphere, it becomes a valuable technique with more complex geometries. When positive, we are outside the sphere when negative we are inside and when zero we are exactly on its surface. As the name suggests, it provides a measure which can be positive or negative. This now belongs to a family of functions called signed distance functions. We can change it in such a way that instead of a boolean value, it returns a distance:
In the previous post we have used a function called sphereHit which indicated whether a point was inside a sphere or not: We would like a way of estimating how far a ray can travel without hitting a piece of geometry. In order for this technique to work, we need to be able to estimate the distance from our geometry. If we want to use real time volumetric rendering, we need to find better a more efficient solution. The performance of a shader suffers immensely by adding loops. What makes raymarching with constant step very inefficient is the fact that rays advances by the same amount every time, regardless of the geometry that fills the volumetric world.
#GLSL VOLUMETRIX RAY MARCHING UPGRADE#
Unity is free, but you can upgrade to Unity Pro or Unity Plus subscriptions plans to get more functionality and training resources to power up your projects. Before that, need to focus on a better implementation of the raymarch technique.
The post Surface Shading will be dedicated entirely to give threedimensionality to volumetric geometries. Raymarching with constant step can be implemented with the following code:įixed4 raymarch (float3 position, float3 direction)Īs seen already, it renders unsexy, flat geometries: If that’s the case, we draw red pixel, otherwise a white one. Each ray is extended by STEP_SIZE in the view direction, until it hits something.
The first implementation of raymarching introduced in Volume Rendering used a constant step. The rest of this post will provide different implementations for the raymarch function. Return raymarch (worldPosition, viewDirection) O.wPos = mul(_Object2World, v.vertex).xyz įloat3 viewDirection = normalize(i.wPos - _WorldSpaceCameraPos) The barebone shade that allows us to do this is:įloat3 wPos : TEXCOORD1 // World position We can manually extends those rays, making them hit custom geometries that exists only within the shader code. To compensate for this, we have have introduced a technique called raymarch. What we have in a fragment shader is the position of the point we are rendering (in world coordinates), and the view direction from the camera. Loosely speaking, the standard behaviour of Unity 5’s lighting engine stops the rendering when a ray from the camera hits the surface of an object. There is no built-in mechanism for those rays to penetrate within the surface of an object.