Drawing Tools Subs or Functions with Demo

[TerryRitchie]

Hey @bplus I've been playing around with your image to sphere code. (cool by the way!)

I've whittled it down to the bare essentials and understand most of it. Could you please explain to me what lines 54 and 57 of the code are doing?

Code: (Select All)

CONST wW = 1280 '  screen width
CONST wH = 720 '   screen height
DIM x AS INTEGER ' x center of sphere
DIM y AS INTEGER ' y center of sphere
DIM map AS LONG '  map image

SCREEN _NEWIMAGE(wW, wH, 32)
map = _LOADIMAGE("worldmap.png")
x = wW / 2 '                                    center sphere horizontally on screen
y = wH / 2 '                                    center sphere vertically on screen

WHILE _KEYDOWN(27) = 0 '                        ESC key pressed?
    xoff = (xoff + 4) MOD (_WIDTH(map) + 1) '   no, rotate left (can't go right because of MOD use)
    projectImagetoSphere map, x, y, 300, xoff ' map image to sphere
    _DISPLAY
    _LIMIT 60
WEND

SUB projectImagetoSphere (image AS LONG, x0 AS INTEGER, y0 AS INTEGER, sr AS INTEGER, xo AS INTEGER)

    ' image : image passed in
    ' x0    : center x location of sphere
    ' y0    : center y location of sphere
    ' sr    : sphere radius
    ' xo    : image x offset

    ' Note: use x1 = _HYPOT(r, y) to map to a funnel structure

    DIM iW AS INTEGER '        width of image
    DIM iH AS INTEGER '        height of image
    DIM r AS SINGLE '          half image height
    DIM scale AS SINGLE '      proportion of sphere radius to image height
    DIM x AS INTEGER '         location along horizontal line within sphere
    DIM y AS INTEGER '         vertical location within image
    DIM x1 AS SINGLE '         length of horizontal line within sphere
    DIM tv AS SINGLE
    DIM tu AS SINGLE
    DIM pc AS _UNSIGNED LONG ' POINT on image
    DIM oSource AS LONG '      calling SOURCE

    oSource = _SOURCE '                                        get calling source
    _SOURCE image '                                            POINT data will be retrieved from image
    iW = _WIDTH(image) '                                       get width of image
    iH = _HEIGHT(image) '                                      get height of image
    r = iH / 2 '                                               calculate image half height
    scale = sr / r '                                           calculate proportion of radius to image height

    y = -r '                                                   start at top of image
    DO '                                                       begin vertical loop
        x1 = SQR(r * r - y * y) '                              length of line across sphere at y location
        tv = (_ASIN(y / r) + 1.5) / 3
        x = -x1 + 1 '                                          start at left side of sphere
        DO '                                                   begin horizontal loop
            tu = (_ASIN(x / x1) + 1.5) / 6
            pc = POINT((xo + tu * iW) MOD iW, tv * iH)
            PSET (x * scale + x0, y * scale + y0), pc
            x = x + 1 '                                        move one pixel across image to the right
        LOOP UNTIL x > x1 '                                    leave when right side of image reached
        y = y + 1 '                                            move one pixel down the image
    LOOP UNTIL y > r '                                         leave when bottom of image reached
    _SOURCE oSource '                                          restore calling source

END SUB