draw sines at higher freq
For a given «visual accuracy», you need to sample the sine at a sufficient number of time-steps per period.
At some point the display pixel density will be to low to render a sine accurately.
For waveform editors (that usually have access to only a finite rate sampled waveform, not a continously defined trigonometric function),  I assume that some practical approximation to the sinc(x) function is used to interpolate those samples to the desired density. There is still a question of what to do when the display is the limiting factor, rather than the input.