THE CARMACK ARCHIVE

The EGA could not redraw the screen fast enough, so scrolling moved into hardware registers and only changed tiles were redrawn. ← → to scroll, or run it on auto. The bar is the redraw: adaptive stays near the floor.

; the reconstruction:
; scroll via CRTC_START + Horizontal Pel Panning: zero pixel writes.
; on reaching the edge, jolt: compare tile IDs, redraw only mismatches.
; Keen 4-6: wrap at the 64K aperture, redraw the leading edge only.
redrawn = changed_tiles / total_tiles   ; ~16%, not 100%

One ray per column, integer grid walk, no floating point unit, no division. WASD / arrows to walk the map. R toggles the rays, T toggles texture.

; WOLFSRC/WL_DR_A.ASM, AsmRefresh. the inner march:
vertentry:
 test [BYTE tilemap+si],0ffh
 jnz hitvert
passvert:
 add bx,[xtilestep]          ; 16.16 fixed point DDA
 ; ...
 jmp vertcheck

Quake's animated lighting is twelve text strings. Each frame: k = (time*10 % len); value = (map[k]-'a')*22. The flame height follows the string. Assign a style to each torch.

; WinQuake/r_light.c:33, R_AnimateLight
i = (int)(cl.time*10);
k = i % cl_lightstyle[j].length;
k = cl_lightstyle[j].map[k] - 'a';
k = k*22;
d_lightstylevalue[j] = k;

One cross product per node sorts the map: near side always, far side only if visible. Drag the viewpoint and watch the draw order recompute on both the map and the tree.

; linuxdoom-1.10/r_bsp.c:552
side = R_PointOnSide (viewx, viewy, bsp);
R_RenderBSPNode (bsp->children[side]);       ; near: always
if (R_CheckBBox (bsp->bbox[side^1]))
    R_RenderBSPNode (bsp->children[side^1]); ; far: maybe

Float bits are piecewise log-linear, so an integer shift-and-subtract approximates a logarithm. Drag the input and watch the guess converge. The amber bars are error, on a log scale.

folklore: not his

; code/game/q_math.c:552
i  = * ( long * ) &y;              // evil floating point bit level hacking
i  = 0x5f3759df - ( i >> 1 );    // what the fuck?
y  = * ( float * ) &i;
y  = y * ( threehalfs - ( x2 * y * y ) );   // 1st iteration