真的很强，万分感谢！, weixin_43648549:
In those cones of light we see in reality, we are not seeing actual light rays coming from the light and hitting the floor, what we are seeing is light being reflected by participant media in the atmosphere, those are particles such as haze, fog, dust or smoke that are present pretty much every where. The reason we do all this work with ray marching to get different points in the environment is because with those we can now simulate the presence of participant media in the atmosphere. In the case the ray doesn’t intersect any object, the result will be the exact number δ of points. Illuminance(照明度). This is not really that much complicated, given that you have a good design in your engine, because all you need beside the point of the light is a normal (the direction of the spotlight) and an angle (describes the volume of the cone). Volume ray casting, sometimes called volumetric ray casting, volumetric ray tracing, or volume ray marching, is an image-based volume rendering technique.It computes 2D images from 3D volumetric data sets (3D scalar fields).Volume ray casting, which processes volume data, must not be mistaken with ray casting in the sense used in ray tracing, which processes surface data. To choose this value we also need to take into account the objects in the scene, because the value should be such that it enables the ray to sample points further than the objects (otherwise some objects will not be rendered). The second term can be calculated two different ways.

If the ray does intersect with objects, the closest intersection point is saved, otherwise this process won’t affect the ray sampling. Direkte Verfahren visualisieren das Volumen ohne die Erzeugung solcher Zwischendaten. To describe particles of some sort of participant media it’s necessary to have an absorption coefficient \kappa_{a}, a scattering coefficient \kappa_{s} and a phase function \rho(\alpha), which describes the angular distribution of light scattering at a point in the medium (Jarosz08). Right: Constant density. The thing is, these scenes that we are creating, like the ones I created on my previous ray tracing post, are essentially scenes in a vacuum.

Next it’s necessary to start sampling the ray. Unlike ray tracing, volume ray casting does not spawn secondary rays. Volume ray casting, sometimes called volumetric ray casting, volumetric ray tracing, or volume ray marching, is an image-based volume rendering technique. 3）Ray marching是所谓的光线行进，它只是一种通用的模拟方法，所以它的光线的起点和终点不能一概而论， 但是它的射线和Ray casting的射线有一个共同点，就是它沿着起点开始，每隔一定间隔就停下来做一次计算，再继续前行。具体算什么要看实现的是什么功能。 Now, given the origin of the ray (the camera/eye position) and this last sampled point, the user decides on the number of appropriate samples. The process begins by first using the Ray Tracing technique to check for intersections between the ray and the objects in the scene.
In other words, given the origin of the ray, the last sampled point and a number δ of samples, between the origin and the last point the process will generated δ points that are equidistant from each other (as seen on the figure above where the points are at a distance d from each other). Irradiance(辐照度) 给你点个赞, TTC_TTS: Then you just need to check if a shadow ray is “inside” the cone and then see if it hits the source. Volume ray casting is classified as an image-based volume rendering technique, as the computation emanates from the output image and not the input volume data, as is the case with object-based techniques. [1] When the context/application is clear, some authors simply call it ray casting. Maybe it’s just me, but I actually do believe the effect of volumetric light is something that people interested in computer graphics are curious about when they start implementing different kinds of global illumination algorithm. It computes 2D images from 3D volumetric data sets (3D scalar fields). 1. Iglesias Guitian, The Visual Computer 2008), https://en.wikipedia.org/w/index.php?title=Volume_ray_casting&oldid=982052709, Creative Commons Attribution-ShareAlike License, ImageVis3D – an Open Source GPU volume ray casting implementation, Volumetric Fog & Mist - a Unity plugin for rendering volumetric fog and clouds, This page was last edited on 5 October 2020, at 22:22. Here we see the result of running the algorithm for both a constant and variable density atmosphere in a scene with only light sources and no objects.


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