This script works around pixi-spine issue 68 by multiplying all additive slots rgb values by alpha.

pixi-spine_issue_68_workaround.py

#!/usr/bin/python3

import os
import json
import math
from collections import OrderedDict

def multiply_rgb_by_alpha_and_set_alpha_to_1(hex_color):
	# Turn hex to float values
	rgba = []
	for i in range(0,8,2):
		rgba.append(int('0x' + hex_color[i:i + 2], 0) / 255)
	
	# Multiply rgb values by alpha
	for i in range(3):
		rgba[i] *= rgba[3]
	
	# Set alpha to 1
	rgba[3] = 1.0
	
	# Convert back to hex
	new_hex_color = ''
	for i in range(4):
		hex_value = hex(int(rgba[i] * 255))[2:]
		if len(hex_value) == 1:
			hex_value = '0' + hex_value
		new_hex_color += hex_value
	
	return new_hex_color

if __name__ == '__main__':
	import argparse
	parser = argparse.ArgumentParser(description='This script works around pixi-spine issue 68 by multiplying all'
		'additive slots rgb by alpha.')
	parser.add_argument('spine_files', metavar='Spine .json files', nargs='+',
		help='an integer for the accumulator')
	args = parser.parse_args()

	for spine_file in args.spine_files:
		spine_file = os.path.join(os.getcwd(), spine_file)
		print('Input file: ' + spine_file)
		
		file_split_ext = os.path.splitext(spine_file)
		output_file = file_split_ext[0] + '_-_issue_68_work_around' + file_split_ext[1]
		
		with open(spine_file) as f:
			spine_obj = json.load(f, object_pairs_hook=OrderedDict)

		slot_defaults = spine_obj['slots']
		slot_anims = spine_obj['animations']['animation']['slots']
		for slot_default in slot_defaults:
			name = slot_default['name']

			# Perform first on all the non animated values (defaults)
			if not 'blend' in slot_default:
				continue
			
			if not slot_default['blend'] == 'additive':
				continue
			
			if 'color' in slot_default:
				slot_default['color'] = multiply_rgb_by_alpha_and_set_alpha_to_1(slot_default['color'])
			
			# Do the same to animated values
			if not name in slot_anims:
				continue
			
			if not 'color' in slot_anims[name]:
				continue
			
			for keyframe in slot_anims[name]['color']:
				keyframe['color'] = multiply_rgb_by_alpha_and_set_alpha_to_1(keyframe['color'])

		with open(output_file, 'w') as f:
			json.dump(spine_obj, f)

		print('Output file: ' + output_file)