Technical note: Filling trim cracks on GPU-rendered solid models

We present an algorithm for improving the rendering appearance of CAD models with trimmed freeform surfaces when evaluated on graphics processing units (GPUs). Rendering on client GPUs allows mechanical CAD to embrace cloud computing by storing a single auto-synchronized model file in the cloud and transferring only minimal data (control points, trim curves, etc.) to the client nodes for local evaluation/rendering. However, current parallel algorithms that directly evaluate and render trimmed surfaces by masking the trims, without tessellating along the trim curves, suffer from ''cracks'' along the trim boundaries. We have developed a hybrid CPU-GPU algorithm to remove these artifacts in the rendering stage for a smooth, color- and shading-matched appearance. After dynamically detecting the cracks, our algorithm selectively fills in the affected pixels using a GPU fragment program, while avoiding artifacts at silhouettes. We have implemented this algorithm to demonstrate improvements in the appearance of solid models directly evaluated and rendered on the GPU.