How to convert pixel map to voltage/angles?
So, the conversion from rectangular coordinates to angles is really just a bunch of trigonometric functions; that's not hard to do on paper (if your mirror is x meters from the wall, and you want to light up a point y meters right of the perpendicular, that angle is arcsin(y/x); do a drawing to clarify for yourself).
But:
Your approach isn't great. The mirror is an object with a mass and thus, hysteresis. Accelerating and breaking it is complicated, takes time and energy.
Your laser on the other hand can nearly arbitrarily fast be pulsed.
So, assuming you have one voice coil to deflect the mirror in vertical direction, and one in horizontal:

Let the mirror do a full row scan as one continuous swipe. It's very possible that the easiest way of doing so is a simple current DAC, which you also find in cameras to control optical elements (stabilizers, autofocus), for example the AD5398A.
Then, advance one row with the other coil, and do the swipe (hint: might be clever to do it in the opposite direction)
all the while, you turn on your laser at the right time instants – not at inidividual &quot;discrete&quot; angles, but based on knowing that mirror travels continuously, at the right time.

That gives you a simple three-DAC system: One DAC for row slides, one DAC to define the vertical deflection, and one fast DAC for the laser. Your horizontal resolution is only defined by how quickly you can control the laser, your vertical by how many individual rows you can do.