Are all computer graphics rendered using polygons? What I mean is, some computer geometries are mathematically represented in the form of equations (for example, CAD software).

Does the computer first have to tessellate those geometries before it can properly render the visualization to screen or are there other methods of getting the picture to the screen without having to tessellate an object?

Edit: I guess more specifically focused on the GPU. How dose the GPU do it? what kind of inputs dose it require, ie, what model formats dose the GPU work with? can it use a perfect mathematical representation directly or dose it tessellate the model itself before actually rendering to screen or dose the GPU require a tessellated model to begin with.

Also, what i mean by tessellation is the way a computer breaks down a mathematical representation of an object into a surface approximation of polygons (almost always triangles). The more polygons used, the closer the surface is to the actual object.