Solid5 4/8

 BBS: Inland Empire Archive
Date: 03-21-93 (03:42)             Number: 354
From: RICH GELDREICH               Refer#: NONE
  To: ALL                           Recvd: NO  
Subj: Solid5 4/8                     Conf: (2) Quik_Bas

'Page 4 of SOLID5.BAS begins here.
        D1 = 0: D2 = 0: D3 = 0
    CASE "0"
        R1 = 0: R2 = 0: R3 = 0
        D1 = 0: D2 = 0: D3 = 0
    CASE "+"
        D3 = D3 + 2
    CASE "-"
        D3 = D3 - 2
    CASE CHR$(27)
        END
    CASE CHR$(0) + CHR$(72)
        dz = dz - 20
    CASE CHR$(0) + CHR$(80)
        dz = dz + 20
    CASE CHR$(0) + CHR$(77)
        dx = dx - 20
    CASE CHR$(0) + CHR$(75)
        dx = dx + 20
    END SELECT
LOOP

'"Culls" the polygons which aren't visible to the viewer. Also shades
'each polygon using Lambert's law.
SUB CullPolygons
    'This algorithm for removing hidden faces was developed by Dave _
Cooper.
    'There is another method, by finding the dot product of the
    'plane's normal and the viewing vector, but this algorithm is
    'much faster because of its simplicity(and lack of floating point
    'calculations).
    FOR a = 0 TO MaxPolys
        P1 = Polys(a).P1
        P2 = Polys(a).P2
        P3 = Polys(a).P3

        IF Points(P1).YView <= Points(P2).YView THEN
            IF Points(P3).YView < Points(P1).YView THEN
                PTop = P3
                PNext = P1
                PLast = P2
            ELSE
                PTop = P1
                PNext = P2
                PLast = P3
            END IF
        ELSE
            IF Points(P3).YView < Points(P2).YView THEN
                PTop = P3
                PNext = P1
                PLast = P2
            ELSE
                PTop = P2
                PNext = P3
                PLast = P1
            END IF
        END IF

        XLow = Points(PTop).XView
        YLow = Points(PTop).YView

        XNext = Points(PNext).XView
        XLast = Points(PLast).XView

        IF XNext <= XLow AND XLast >= XLow THEN
            Polys(a).Culled = True
        ELSEIF XNext >= XLow AND XLast <= XLow THEN
            Polys(a).Culled = False
        ELSE
            YNext = Points(PNext).YView
            YLast = Points(PLast).YView
            IF ((YNext - YLow) * 256&) \ (XNext - XLow) < ((YLast - _
YLow) * 256&) \ (XLast - XLow) THEN
                Polys(a).Culled = False
            ELSE
                Polys(a).Culled = True
            END IF
        END IF

    NEXT
END SUB

'Enters a line into the edge list. For each scan line, the line's
'X coordinate is found. Notice the lack of floating point math in this
'subroutine.
SUB DrawLine (xs, ys, xe, ye, EdgeList() AS EdgeType)

    IF ys > ye THEN SWAP xs, xe: SWAP ys, ye

    IF ye < 0 OR ys > 199 THEN EXIT SUB

    IF ys < 0 THEN
        xs = xs + ((xe - xs) * -ys) \ (ye - ys)
        ys = 0
'Continued on page 5

--- MsgToss 2.0b
 * Origin: Computer Co-Op - Voorhees, NJ | Ted Hare (1:266/29)