import bpy
import math


class VertexAccumulator:
    # use this class when you can't come up with a good deterministic numbering scheme for your vertices.

    def __init__(self):
        self.verts_ = []
        self.vertIdxs = {}

    def keyFor(v):
        return "%f,%f,%f"%(v[0], v[1], v[2])

    def idxFor(self, v):
        key = VertexAccumulator.keyFor(v)
        rval = self.vertIdxs.get(key)
        if None==rval:
            rval = len(self.verts_)
            self.vertIdxs[key] = rval
            self.verts_.append(v)
        return rval

    def verts(self):
        return self.verts_


def image_to_mesh(img):
    pix = img.pixels[:]
    w = img.size[0]
    h = img.size[1]

    def is_solid(pix, off):
        return pix[off]  < 0.5

    va = VertexAccumulator()

    faces = []
    for y in range(h):
        for x in range(w):
            off= 4* ( y*w + x )
            solid = is_solid(pix, off)

            x1 = x
            x2 = x + 1
            if True:
                y1 = y
                y2 = y+1
            else:
                y2 = h-y
                y1 = y2-1
            if solid:
                i0 = va.idxFor([x1, y1, 0])
                i1 = va.idxFor([x2, y1, 0])
                i2 = va.idxFor([x1, y2, 0])
                i3 = va.idxFor([x2, y2, 0])
                i4 = va.idxFor([x1, y1, -1])
                i5 = va.idxFor([x2, y1, -1])
                i6 = va.idxFor([x1, y2, -1])
                i7 = va.idxFor([x2, y2, -1])

                # top
                faces.append( [i0, i1, i3, i2,] )
                # bottom
                faces.append([i4, i6, i7, i5,])

                if x <1 or not is_solid(pix, off-4):
                    # x--
                    faces.append( [ i0, i2, i6, i4])

                if x+1 >w or not is_solid(pix, off+4):
                    faces.append( [i1, i5, i7, i3])
                if y<1 or not is_solid(pix, off-4*w):
                    faces.append( [i0, i4, i5, i1])
                if y+1>h or not is_solid(pix, off+4*w):
                    faces.append( [ i2, i3, i7, i6])

    mesh = bpy.data.meshes.new('stencil')
    mesh.from_pydata(va.verts(), [], faces)
    mesh.show_normal_face = True

    return mesh

def mission1(scn):
    img = bpy.data.images['frog-trace-post.png']
    #img = bpy.data.images['test.png']
    mesh = image_to_mesh(img)

    obj = bpy.data.objects.new("stencil", mesh)

    scn.objects.link(obj)
    s = 1/max(img.size[0], img.size[1])
    print(s)
    obj.scale = (s,s,1)
    print(obj.scale)

mission1(bpy.context.scene)