backend.py

import json
from flask import Flask
from flask_cors import CORS

from PIL import Image
import numpy as np
import potrace
import cv2
import os
import sys
import traceback
import multiprocessing


app = Flask(__name__)
CORS(app)

#FRAMES = 5258
FRAME_DIR = 'frames'
frame_latex = 0


def png_to_np_array(filename):
    img = Image.open(filename)
    data = np.array(img.getdata()).reshape(img.size[1], img.size[0], 3)
    bindata = np.zeros((img.size[1], img.size[0]), np.uint32)
    for i, row in enumerate(data):
        for j, byte in enumerate(row):
            bindata[img.size[1]-i-1, j] = 1 if sum(byte) < 127*3 else 0
        #     print('###' if bindata[i, j] == 1 else '   ', end='')
        # print()
    return bindata

def png_to_svg(filename):
    data = png_to_np_array(filename)
    bmp = potrace.Bitmap(data)
    path = bmp.trace()
    return path

frame_coords = []

def gefd(frame_latexs):
    for i in range(frame_latexs):

        latex = []

        path = png_to_svg('frames/frame%d.png' % (i+1))

        for curve in path.curves:
            segments = curve.segments
            start = curve.start_point
            for segment in segments:
                x0, y0 = start
                if segment.is_corner:
                    x1, y1 = segment.c
                    x2, y2 = segment.end_point
                    latex.append('((1-t)%f+t%f,(1-t)%f+t%f)' % (x0, x1, y0, y1))
                    latex.append('((1-t)%f+t%f,(1-t)%f+t%f)' % (x1, x2, y1, y2))
                else:
                    x1, y1 = segment.c1
                    x2, y2 = segment.c2
                    x3, y3 = segment.end_point
                    latex.append('((1-t)((1-t)((1-t)%f+t%f)+t((1-t)%f+t%f))+t((1-t)((1-t)%f+t%f)+t((1-t)%f+t%f)),\
                    (1-t)((1-t)((1-t)%f+t%f)+t((1-t)%f+t%f))+t((1-t)((1-t)%f+t%f)+t((1-t)%f+t%f)))' % \
                    (x0, x1, x1, x2, x1, x2, x2, x3, y0, y1, y1, y2, y1, y2, y2, y3))
                start = segment.end_point

        frame_coords.append(latex)

@app.route('/')
def index():
    return json.dumps(frame_coords)

@app.route('/app')
def app_():
    return render_template('index.html')

if __name__ == '__main__':
    frame_latex =  range(len(os.listdir(FRAME_DIR)))
    with multiprocessing.Pool(processes = multiprocessing.cpu_count()) as pool:
        print('Processing %d frames... Please wait for processing to finish before running on frontend\n' % len(os.listdir(FRAME_DIR)))

    try:
        frame_latex = pool.map(gefd, frame_latex)
    except cv2.error as e:
        print('[ERROR] Unable to process one or more files. Remember image files should be named <DIRECTORY>/frame<INDEX>.<EXTENSION> where INDEX represents the frame number starting from 1 and DIRECTORY and EXTENSION are defined by command line arguments (e.g. frames/frame1.png). Please check if:\n\tThe files exist\n\tThe files are all valid image files\n\tThe name of the files given is correct as per command line arguments\n\tThe program has the necessary permissions to read the file.\n\nUse backend.py -h for further documentation\n')            

        print('-----------------------------')

        print('Full error traceback:\n')
        traceback.print_exc()
        sys.exit(2)
    
    app.run()