Abstract—Lines drawn over or in place of shaded 3D models can often provide greater comprehensibility and stylistic freedom than shading alone. A substantial challenge for making stylized line drawings from 3D models is the visibility computation. Current algorithms for computing line visibility in models of moderate complexity are either too slow for interactive rendering, or too brittle for coherent animation. We introduce two methods that exploit graphics hardware to provide fast and robust line visibility. First we present a simple shader that performs a visibility test for high-quality, simple lines drawn with the conventional implementation. Next we offer a full optimized pipeline that supports line visibility and a broad range of stylization options. 1

Figure 1: On the left is one frame of an elephant animation visualizing estimated curvature. Blue indicates concave areas, red indicates convex areas, and green indicates saddle-shape areas. The middle is using surface curvature to approximate ambient occlusion. On the right is an orange volume with ∼1.5 billion vertices with Lambertian shading and ambient occlusion which we estimate curvature on in 39.3 ms. Surface curvature is used in a number of areas in computer graphics, including texture synthesis and shape representation, mesh simplification, surface modeling, and non-photorealistic line drawing. Most real-time applications must estimate curvature on a triangular mesh. This estimation has been limited to CPU algorithms, forcing object geometry to reside in main memory. However, as more computational work is done directly on the GPU, it is increasingly common for object geometry to exist only in GPU memory. Examples include vertex skinned animations and isosurfaces from GPU-based surface reconstruction algorithms. For static models, curvature can be pre-computed and CPU algorithms are a reasonable choice. For deforming models where the geometry only resides on the GPU, transferring the deformed mesh back to the CPU limits performance. We introduce a GPU algorithm for estimating curvature in real-time on arbitrary triangular meshes. We demonstrate our algorithm with curvature-based NPR feature lines and a curvature-based approximation for ambient occlusion. We show curvature computation on volumetric datasets with a GPU isosurface extraction algorithm and vertex-skinned animations. Our curvature estimation is up to ∼18x faster than a multithreaded CPU benchmark. CR Categories: I.3.3 [Computer Graphics]: Picture/Image Generation—Line and curve generation; I.3.3 [Computer Graphics]:

Surface curvature is used in a number of areas in computer graphics including mesh simplification, surface modeling and denoising, feature detection, and non-photorealistic line drawing techniques. Most applications must estimate surface curvature, due to the use of discrete models such as triangular meshes. Until recently, curvature estimation has been limited to CPU algorithms, forcing object geometry to reside in main memory. More computational work is being done directly on the GPU, and it is increasingly common for object geometry to