Intel i86W Manual page 193

PROGRAMMING EXAMPLES
II
RENDERING PROCEDURE
II 16-bit pixels. 16-bit Z-buffer
and 3. Xl. Ra
II
Determine alignment of starting-point
acc_init Ra. Rb. Rc. Rd. Fa. Fah II Initialize accumulators
subs 4. Ra. Rb
II
4 - alignment
subs dX. Rb. dX
II
Adjust dX by Xl alignment
II
If dX <= 0. then right end is in same set as left end
and 3. dX. Rb
II
Determine alignment of right end
zmask Ra. Rb. Rc. Rd
II
Prepare both left- and right-end masks
left_end::
II
Handle boundary conditions
d.faddz aZ. iZ3. aZ II Interpolate 2 even Z values
adds -8. FBP. FBP
II
Anticipate autoincrement
d.faddz aZ. iZl. aZ
II
Interpolate 2 odd Z values
adds -8. ZBP. ZBP
II
Anticipate autoincrement
d.form lZmask. newz II Mask 4 new Z values
fld.d 8CZBP). oldz
II
Fetch 4 old Z values
d.faddp aBo iB. aB
II
Interpolate 4 blue intensities
mov -4. Ra
II
Loop increment: 4 pixels
d.faddp aGo iG. aG
II
Interpolate 4 green intensities
adds -4. dX. dX
II
Prepare dX for bla at end of loop
d.faddp aR. iR. aR II Interpolate 4 red intensities
bla Ra. dX. Ll
II
Initial ize LCC
d.form f0. newi
II
Move 4 new pixels to 64-bit reg
adds 5. dX. r0
II
Are there any whole sets CdX
<
-5)?
Ll: d.fzchks oldz. newz. newz II Mark closer points in PM[7 .. 4]
bc short_segment
II
Get out now if no whole set
d.fnop
II
fld.d 16CZBP). oldz
II
Fetch 4 old Z values
inner_loop:: II Handle all interior points
d.faddz aZ. iZ3. aZ
II
Interpolate 2 even Z values
nop
II
d.faddz aZ. iZl.
at
II
Interpolate 2 odd Z values
fst·d newz. 8CZBP)++ II Update Z buf from prior loop
d.form f0. newz
II
Move 4 new Z values to 64-bit reg
nop
II
d.fzchks f0. f0. f0
II
Shift PM[7 .. 4] to PM[3 .. 0]
mov - 5 . · Rb II -5 mod 4
=
3. aligned right end
d.faddp aBo iB. aB
II
Interpolate 4 blue intensities
pst.d newi. 8CFBP)++ II Store pixels indicated by PM [3 .. 0]
d.faddp aGo iG. aG
II
Interpolate 4 green intensities
xor Rb. dX. r0 II Are we at an aligned right end?
d.faddp aR. iR. aR
II
Interpolate 4 red intensities
bc aligned_end
II
Taken if at an aligned right end
-->
d.form f0. newi
II
Move 4 new pixels to 64-bit reg
bla Ra. dX. inner~loop II Loop if not at end of line segment
d.fzchks oldz. newz. newz
II
Mark closer points in PM[7 .. 4]
fld·d 16CZBP). oldz II Fetch 4 old Z values for next loop
II
End of inner_loop. Right end not aligned
Example 9-21. 3-D Rendering (1 of 2)
9-31