ray trace & rasterization

Computer graphics algorithms for rendering, or image synthesis, take one of two complementary approaches.
One family of algorithms loop over the pixels in the image, computing for each pixel, the first object visible at that pixel; this approach is called ray tracing because it solves the geometric problem of intersecting a ray from the pixel into the objects.A second family of algorithms loops over the objects in the scene, computing for each object the pixels covered by that object. Because the resulting per-object pixels (called fragments) are formatted for a raster display, this approach is called rasterization.

来自 GPU Ray Tracing