from kivy.clock import Clock
from kivy.uix.floatlayout import FloatLayout
from kivy.core.window import Window
from kivy.graphics import RenderContext
from kivy.properties import StringProperty


class ShaderWidget(FloatLayout):
    # property to set the source code for fragment shader
    fs = StringProperty(None)

    def __init__(self, **kwargs):
        # Instead of using Canvas, we will use a RenderContext,
        # and change the default shader used.
        self.canvas = RenderContext()

        # call the constructor of parent
        # if they are any graphics object, they will be added on our new canvas
        super(ShaderWidget, self).__init__(**kwargs)

        # We'll update our glsl variables in a clock
        Clock.schedule_interval(self.update_glsl, 1 / 60.0)

    def on_fs(self, instance, value):
        # set the fragment shader to our source code
        shader = self.canvas.shader
        old_value = shader.fs
        shader.fs = value
        if not shader.success:
            shader.fs = old_value
            raise Exception("failed")

    def update_glsl(self, *largs):
        self.canvas["time"] = Clock.get_boottime()
        self.canvas["resolution"] = list(map(float, self.size))
        # This is needed for the default vertex shader.
        win_rc = Window.render_context
        self.canvas["projection_mat"] = win_rc["projection_mat"]
        self.canvas["modelview_mat"] = win_rc["modelview_mat"]
        self.canvas["frag_modelview_mat"] = win_rc["frag_modelview_mat"]