-- demo\rosetta\Hough_transform.exw
include pGUI.e

function hypot(atom a,b) return sqrt(a*a+b*b) end function

function hough_transform(imImage im, integer width=460, height=360)
    height = 2*floor(height / 2)
    integer xsize = im_width(im),
            ysize = im_width(im)
    sequence ht = repeat(repeat(repeat(255,3),width),height)
    sequence canvas = repeat(repeat(255,width),height)
    atom rmax = hypot(xsize, ysize),
         dr = 2*(rmax / height),
         dth = (PI / width)
    for y=0 to ysize-1 do
        for x=0 to xsize-1 do
            integer {r,g,b} = im_pixel(im, x, y)
            if r!=255 then
                for k=1 to width do
                    atom th = dth*(k-1),
                         r2 = (x*cos(th) + y*sin(th))
                    integer iry = (height/2 + floor(r2/dr + 0.5))+1,
                            cik = canvas[iry][k] - 1
                    canvas[iry][k] = cik
                    ht[iry][k] = repeat(cik,3)
                end for
            end if
        end for
    end for
    ht = flatten(ht) -- (needed by IupImageRGB)
    Ihandle new_img = IupImageRGB(width, height, ht)
    return new_img
end function

IupOpen()

atom pError = allocate(machine_word())
imImage im1 = imFileImageLoadBitmap("Pentagon.png",0,pError)
if im1=NULL then ?"error opening Pentagon.png" abort(0) end if
Ihandln image1 = IupImageFromImImage(im1),
        image2 = hough_transform(im1),
        label1 = IupLabel(),
        label2 = IupLabel()
IupSetAttributeHandle(label1, "IMAGE", image1)
IupSetAttributeHandle(label2, "IMAGE", image2)

Ihandle dlg = IupDialog(IupHbox({label1, label2}))
IupSetAttribute(dlg, "TITLE", "Hough transform")
IupCloseOnEscape(dlg)
IupShow(dlg)

IupMainLoop()
IupClose()