Rotozoom without the skew

[OldMoses]

A very interesting thread that got me to investigate how Rotozoom actually works. An extra slice of raisin pie to Mr. Jarvis (as they used to say in Easyriders mag) for getting it fixed. I never noticed the issue since I never had occasion to use different scale factors.

While picking the SUB apart I noticed that I could tweak it to work with various parts of my typical vector library scheme and my own idiosyncrasies. Here's the work in progress that I've been playing with:

Code: (Select All)

TYPE V2
    x AS SINGLE
    y AS SINGLE
END TYPE

DIM SHARED img&
DIM sp AS V2
SCREEN _NEWIMAGE(1024, 512, 32)
img& = _NEWIMAGE(256, 256, 32)
MakeImage

deg1! = _D2R(1)
sx! = 1 '                                                       X Scale factor
sy! = 1 '                                                       Y Scale factor
redo:
sp.x = 128: sp.y = 256
FOR x% = 0 TO 360
    CLS
    LINE (0, _HEIGHT * (3 / 4))-(_WIDTH - 1, _HEIGHT * (3 / 4)), &HFFFFFFFF
    sp.x = sp.x + (SIN(deg1!) * 128)
    sp.y = _HEIGHT * (3 / 4) - (_HEIGHT(img&) / 2) - ABS(COS(_D2R(x%)) * (sy! * 128 - 128))
    'sin0=0 sin90=1 sin180=0 sin270=-1
    'cos0=1 cos90=0 cos180=-1 cos270=0
    RotoZoomV sp, img&, sx!, sy!, x%
    _LIMIT 80
    _DISPLAY
NEXT x%
INPUT "again? ", a$
IF a$ = "y" THEN GOTO redo
END


SUB RotoZoomV (center AS V2, Image AS LONG, xScale AS SINGLE, yScale AS SINGLE, Rotation AS SINGLE)
    'Development progression: Galleon/Bplus/James Jarvis/altered for OldMoses' vector libraries
    DIM AS V2 p(3)
    W& = _WIDTH(Image): WS& = W& / 2 * xScale
    H& = _HEIGHT(Image): HS& = H& / 2 * yScale
    rota! = -0.01745329 * Rotation '                            convert degrees to radians
    FOR i& = 0 TO 3
        p(i&).x = WS& * (1 + 2 * (i& < 2)) '                    i& < 2 return -1 else return 1
        p(i&).y = HS& * (1 + 2 * (i& MOD 3 = 0)) '              i& = 0 or 3 return -1 else return 1
        R2_Roto p(i&), rota! '                                  perform rotation transform
        R2_Add p(i&), center, 1 '                               add center postition to result
    NEXT
    _MAPTRIANGLE (0, 0)-(0, H& - 1)-(W& - 1, H& - 1), Image TO(p(0).x, p(0).y)-(p(1).x, p(1).y)-(p(2).x, p(2).y)
    _MAPTRIANGLE (0, 0)-(W& - 1, 0)-(W& - 1, H& - 1), Image TO(p(0).x, p(0).y)-(p(3).x, p(3).y)-(p(2).x, p(2).y)
END SUB 'RotoZoomV

SUB R2_Roto (v AS V2, ang AS SINGLE) 'transform v, rotating by ang radians
    s! = SIN(ang)
    c! = COS(ang)
    x! = v.x: y! = v.y
    v.x = x! * c! + y! * s!
    v.y = y! * c! - x! * s!
END SUB 'R2_RotZ

SUB R2_Add (v AS V2, s AS V2, scalar AS SINGLE)
    v.x = v.x + s.x * scalar
    v.y = v.y + s.y * scalar
END SUB 'R2_Add

SUB MakeImage
    _DEST img&
    x% = _WIDTH: y% = _HEIGHT: x2% = _SHR(x%, 1): y2% = _SHR(y%, 1)
    COLOR , &H00000000
    CLS
    LINE (x2%, y2%)-(x2%, 0), &HFFFFFFFF
    LINE (x2%, y2%)-(x% - 1, y2%), &HFFFF0000
    LINE (x2%, y2%)-(x2%, y% - 1), &HFF00FF00
    LINE (x2%, y2%)-(0, y2%), &HFF0000FF
    CIRCLE (x2%, y2%), 127
    _DEST 0
END SUB 'MakeImage