Making sphere look smooth without changing its model by using Phong Shading.
Phong shading first interpolates and normalizes normal vectors at each pixel.
Then it uses a combination of diffuse reflection of rough surfaces with specular reflection of shiny surfaces, along with ambient light, to create a Phong reflection, resulting in an optical illusion of a smooth surface.
This demo is implemented using fragment shaders.
The button flat or round takes you first to a sphere in ambient light, then clicking it again takes you to a Phong shaded sphere.