University of Pennsylvania, CIS 565: GPU Programming and Architecture, Project 5 - DirectX Procedural Raytracing
- Author: Chhavi Sharma (LinkedIn)
- Tested on: Windows 10, Intel Xeon CPU E5-2687W v3 @ 3.10GHz 22GB, NVIDIA TITAN V 12GB (SIGLab-VR1)
In this project, we use Microsoft's DirectX Raytracing API to ray trace procedural geometries. The code is divided into two categories, the CPU pipline for allocation and setup of DXR buffers, and, the the GPU rendering pipeline to execute the ray tracing. Microsoft introduced the DirectX Raytracing (DXR) API to allow ease of use of GPU-accelerated ray tracing in DirectX and also for interoperability with the DirectX rasterization.
Raytracing, is a rendering technique for generating an image by tracing the path of light through pixels in an image plane. In ray tracing, a light ray is shot from the camera center through each pixel. It is traced as it intersects different objects in the scene. At each interseciton, the ray is sent to to the light source, and, other rays are generated based on the material properties ( eg. reflection). If the ray interseacts another object on its way to light, then it is categorised as a shadow ray and color is assosiated with it accordingly.
This diagram summarizes the DXR execution pipeline for each ray:
DXR also implements special Acceleration Structures namely Bottom Level Acceleration Structure and Top Level Acceleration Structre to speed up the intersection search over all objects in the scene. The BLAS hold unique defifnitions of different categories of objects in the scene. The TLAS hold various instantiations of BLAS objects which could be scaled, translated and rotated. Once these buffers are specified, DXR automatically builds optimised search routines using algorithms suck as KD-Tree search to speed up the process.
We implement the Phong lighting model which is an empirical model of the local illumination of points on a surface using Ambient, Diffuese and Specular lighting. We also implement Schlick's Approximation for Fresnel reflection effects on the objects.
As the recursion depth increases, the frame rate drops. Most of the rays terminate at the light source after a few bounces so there isn't significant FPS drop after depth 6-7. Visibly, there isn't much gain in the the rendering quality therfore recursion depth of 3 is sufficient to render well defined images for the given scene.
Trace Rays | Miss Shaders | Intersection Shaders (Metaballs & AABBS)
Phong Lighting Model Shading, Schlick's Approximation | Closest Hit Shaders
- Error computing Meta-Ball potential, (incorrect range)
- Error computing Shadow Rays
- Error in color computation
