Interactively rendering solid CAD models currently relies on tessellation of the models and passing of the tessellation onto the graphics card (GPU). Direct rendering on the GPU, without a tessellation preprocess, has many advantages -- pixel-level quality, less memory requirements, and less preprocessing, to name a few. However, one of the main problems with existing solutions for rendering solid models directly is the appearance of crack/gap artifacts between faces due to the approximations of the trimming curves. This prevents the usage of direct GPU rendering in CAD systems. In this paper we present a novel solution to the gap problem. The new method combines a unique representation of the faces of the solid model, with fragment shader algorithms that utilize the representation for identifying the surface area to be rendered. This enables us to render the models with high quality in interactive speed without the crack/gap artifacts. We have implemented our method in a ray casting system for viewing CAD solid models and present our results.
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