Henry Packard Moreton

A user-programmable vertex engine

In this paper we describe the design, programming interface, and implementation of a very efficient user-programmable vertex engine. The vertex engine of NVIDIAs GeForce3 GPU evolved from a highly tuned fixed-function pipeline requiring considerable knowledge to program. Programs operate only on a stream of independent vertices traversing the pipe. Embedded in the broader fixed function pipeline, our approach preserves parallelism sacrificed by previous approaches. The programmer is presented with a straightforward programming model, which is supported by transparent multi-threading and bypassing to preserve parallelism and performance. In the remainder of the paper we discuss the motivation behind our design and contrast it with previous work. We present the programming model, the instruction set selection process, and details of the hardware implementation. Finally, we discuss important API design issues encountered when creating an interface to such a device. We close with thoughts about the future of programmable graphics devices.

Displaced subdivision surfaces

In this paper we introduce a new surface representing, the displaced subdivision surface. It represents a detailed surface model as a scalar-valued displacement over a smooth domain surface. Our representation defines both the domain surface and the displacement function using a unified subdivision framework, allowing for simple and efficient evaluation of analytic surface properties. We present a simple, automatic scheme for converting detailed geometric models into such a representation. The challenge in this conversion process is to find a simple subdivision surface that still faithfully expresses the detailed model as its offset. We demonstrate that displaced subdivision surfaces offer a number of benefits, including geometry compression, editing, animation, scalability, and adaptive rendering. In particular, the encoding of fine detail as a scalar function makes the representation extremely compact.

The GeForce 6800

Graphics processing units (GPUs) continue to take on increasing computational workloads and support interactive rendering that approaches cinematic quality. The architectural drivers for GPUs are programmability, parallelism, bandwidth, and memory characteristics. This article describes how one team approached the design problem.

Watertight tessellation using forward differencing

In this paper we describe an algorithm and hardware for the tessellation of polynomial surfaces. While conventional forward difference-based tessellation is subject to round off error and cracking, our algorithm produces a bit-for-bit consistent triangle mesh across multiple independently tessellated patches. We present tessellation patterns that exploit the efficiency of iterative evaluation techniques while delivering a defect free adaptive tessellation with continuous level-of-detail. We also report the rendering performance of the resulting physical hardware implementation.

Reducing shading on GPUs using quad-fragment merging

Current GPUs perform a significant amount of redundant shading when surfaces are tessellated into small triangles. We address this inefficiency by augmenting the GPU pipeline to gather and merge rasterized fragments from adjacent triangles in a mesh. This approach has minimal impact on output image quality, is amenable to implementation in fixed-function hardware, and, when rendering pixel-sized triangles, requires only a small amount of buffering to reduce overall pipeline shading work by a factor of eight. We find that a fragment-shading pipeline with this optimization is competitive with the REYES pipeline approach of shading at micropolygon vertices and, in cases of complex occlusion, can perform up to two times less shading work.

Space-time hierarchical occlusion culling for micropolygon rendering with motion blur

Occlusion culling using a traditional hierarchical depth buffer, or z-pyramid, is less effective when rendering with motion blur. We present a new data structure, the tz-pyramid, that extends the traditional z-pyramid to represent scene depth values in time. This temporal information improves culling efficacy when rendering with motion blur. The tz-pyramid allows occlusion culling to adapt to the amount of scene motion, providing a balance of high efficacy with large motion and low cost in terms of depth comparisons when motion is small. Compared to a traditional z-pyramid, using the tz-pyramid for occlusion culling reduces the number of micropolygons shaded by up to 3.5x. In addition to better culling, the tz-pyramid reduces the number of depth comparisons by up to 1.4x.

Efficient GPU rendering of subdivision surfaces using adaptive quadtrees

We present a novel method for real-time rendering of subdivision surfaces whose goal is to make subdivision faces as easy to render as triangles, points, or lines. Our approach uses standard GPU tessellation hardware and processes each face of a base mesh independently, thus allowing an entire model to be rendered in a single pass. The key idea of our method is to subdivide the u, v domain of each face ahead of time, generating a quadtree structure, and then submit one tessellated primitive per input face. By traversing the quadtree for each post-tessellation vertex, we are able to accurately and efficiently evaluate the limit surface. Our method yields a more uniform tessellation of the surface, and faster rendering, as fewer primitives are submitted. We evaluate our method on a variety of assets, and realize performance that can be three times faster than state-of-the-art approaches. In addition, our streaming formulation makes it easier to integrate subdivision surfaces into applications and shader code written for polygonal models. We illustrate integration of our technique into a full-featured video game engine.