Steps to producing a picture on the screen from all the values in soft3d

FRACUNIT => a constant that is 1.0 in fixed point


Player starts out at:
  playerx = (3 * 64 + 32) * FRACUNIT;
  playery = (3 * 64 + 32) * FRACUNIT;
  playerz = 32 * FRACUNIT;
  playerangle = 0;


The interrupt does the reading of controls and controlling movement.
The play loop itself does nothing but Render the view and shoot the rendered
drawing to the screen.

Movement:
  Pg/Up & Dn change playerz by FRACUNIT
  Home sets playerz to 32.0

  For translation movement:
  Up and Down -
    Checks to see if the move can be made then increments the players position
    by a set amount.

    playerx and playery are updated depending upon angle of movement and
    if the operation succeeds.  In this case if you did not run into a wall.

  Left and Right -
    Changes the playerangle by PLAYERTURNSPEED; in this case 1 degree(?)



View Rendering :

This is done with a call to RF_RenderView int R_PUBLIC.C sending player
position and angle.

This sets the global varibles viewx, viewy, viewz by stripping off most
of the lowest nibbles of the fixed point numbers.  viewangle is set to
playerangle.

SetupFrame is then called:
View buffer is cleared
wallz array is set to MAXZ + 1 ((6 shl 22) + 1)
mapcache_height contents are set to 0xF0
numspans is set to 0
frameon is incremented(?)
viewtilex and viewtiley are set to the respective x and y values shifted
by 22(?)

viewfineangle is set by shifting viewangle by 5
Initializes backvertex;