Louis Bavoil

Image-space horizon-based ambient occlusion

Ambient occlusion is a lighting model that approximates the amount of light reaching a point on a diffuse surface based on its directly visible occluders. It gives perceptual clues of curvature and spatial proximity. Like [Mittring 2007] and [Shanmugam and Arikan 2007], we propose a real-time ambient occlusion computation as a postprocessing pass mainly based on a depth image from the eye’s point of view. This approach requires no scenedependent precomputations and is applicable to dynamic scenes. Our proposed method does not have the overocclusion issue from [Shanmugam and Arikan 2007] and samples inside the radius of influence, unlike [Mittring 2007].

Stencil routed A-Buffer

We have developed a stencil routing algorithm for implementing a GPU accelerated A-Buffer, by using a multisample texture to store a vector of fragments per pixel. First, all the fragments are captured per pixel in rasterization order. Second, a fullscreen shader pass sorts the fragments using a bitonic sort. At this point, the sorted fragments can be blended arbitrarily to implement various types of algorithms such as order independent transparency or layered depth image generation. Since we handle only 8 fragments per pass, we developed a method for detecting overflow, so we can do additional passes to capture more fragments.

Fourier opacity mapping

Whilst the Deep Shadow Maps algorithm for accelerating the rendering of volumetric shadows is a fitting solution for offline applications, it can consume an unbounded amount of memory and is difficult to map well to current graphics hardware. For these reasons alternative methods have been proposed for interactive applications based on the idea of accumulating opacity from volume primitives in depth-based buckets or slices. However, these slice-based methods can introduce objectionable and unstable slice-like artefacts due to undersampling of the depth range, and often many slices are required to overcome these artefacts. Further refinements have been proposed to address this, but they constrain the generality of the algorithm, for example by mandating an assumption of uniform opacity or by dropping support for pre-filtering. We introduce a novel algorithm called Fourier Opacity Mapping (FOM) and we show that it is a good choice for rendering artefact-free pre-filtered volumetric shadows in cases where spatial opacity variations are smooth (e.g. smoke, gas and low-opacity hair). We also show how the algorithm can be generalised to other orthonormal bases.

Multi-layer dual-resolution screen-space ambient occlusion

Ambient occlusion (AO) is a lighting model that approximates the diffuse illumination of a surface based on its directly visible occluders. It can be rendered by tracing rays through the normal-oriented unit hemisphere, and returning the percentage of rays that do no hit any geometry at a distance d < R. Screen-space ambient occlusion (SSAO) is an image-based approach that uses the depth buffer of the current rendered scene as an approximation of its geometry. Therefore, compared to other AO algorithms such as ray tracing, SSAO has the advantage of handling dynamic geometry with significantly lower overhead.

Horizon-split ambient occlusion

The method includes receiving a plurality of graphics primitives for rendering at a GPU of a computer system and rendering graphics primitives into pixel parameters of the pixels of a display, wherein the parameters include pixel depth values and pixel normal values. For each pixel of the display, an ambient occlusion process is performed. The algorithm takes as input a ND-buffer containing pixel depth values and pixel normals. Based on the pixel 3-D position and the pixel normal vector, horizon heights are computed by sampling the ND-buffer and an occlusion term is computed for each pixel based on the horizon heights. Based on the pixel 3-D position, the pixel normal vector, a normal occlusion term is computed by sampling the ND-buffer above the horizon in multiple directions. An ambient occlusion illumination value is computed by combining the horizon occlusion term and the normal occlusion term.

Real time hair simulation and rendering on the GPU

Simulating and rendering realistic hair with tens of thousands of strands is something that until recently was not possible in real time. We present a method for simulating and rendering realistic hair in real time using the power and programmability of modern GPUs (Graphics Processing Units). Our method utilizes new features of graphics hardware (like Stream Output, Geometry Shader and Texture Buffers) that make it possible for all simulation and rendering to be processed on the GPU in an intuitive manner, with no need for CPU intervention or read back. In addition, we propose fast new algorithms for inter-hair collision, and collision detection and resolution of interpolated hair.