Kivy: glsl function plot test

plottest.py

import kivy
kivy.require('1.9.0')

from kivy.app import App
from kivy.uix.effectwidget import EffectWidget, AdvancedEffectBase


effect_plot = '''
uniform float scale_x, scale_y;
uniform float center_x, center_y;
uniform int t;

uniform vec4 line_color, above_color, below_color, grid_color;
uniform float line_thickness, grid_thickness;

float plot_fn(float x) {
	if (t == 0) {
		return x;
	} else if (t == 1) {
		return pow(x, 2);
	} else if (t == 2) {
		return pow(x, 2.0) + x - 1.0;
	} else {
		return sin(x);
	}
}

vec4 effect(vec4 color, sampler2D texture, vec2 tex_coords, vec2 coords) {
	vec4 out_color;
	float value = plot_fn((coords.x - center_x) * scale_x);
	float y_comp = (value * scale_y) + center_y;
	float lthick = line_thickness / 2.0;
	float gthick = grid_thickness / 2.0;
	
	if (coords.y > y_comp + lthick) {
		out_color = above_color;
	} else if (coords.y < y_comp - lthick) {
		out_color = below_color;
	} else {
		out_color = line_color;
	}
	
	if ((coords.y > center_y - gthick && coords.y < center_y + gthick)
			|| (coords.x > center_x - gthick && coords.x < center_x + gthick)) {
		out_color = mix(out_color, grid_color, grid_color.a);
	}
	
	return out_color;
}
'''


class PlotEffect(AdvancedEffectBase):
	def __init__(self, *args, **kwargs):
		super(PlotEffect, self).__init__(*args, **kwargs)
		self.glsl = effect_plot


class Plot(EffectWidget):
	def __init__(self, **kwargs):
		self.plot_effect = PlotEffect(uniforms={
			'scale_x': 0.05,
			'scale_y': 10.0,
			'center_x': 0.0,
			'center_y': 0.0,
			'line_color': (1.0, 0.0, 0.0, 1.0),
			'above_color': (0.0, 0.5, 0.0, 1.0),
			'below_color': (0.0, 0.0, 0.5, 1.0),
			'grid_color': (1.0, 1.0, 1.0, 0.5),
			'line_thickness': 4.0,
			'grid_thickness': 2.0,
			't': 0,
		})
		super(Plot, self).__init__(**kwargs)
		self.effects = [self.plot_effect]
	
	def _update_glsl(self, *args):
		super(Plot, self)._update_glsl()
		self.plot_effect.uniforms['t'] = int(self.canvas['time']) % 4
	
	def on_size(self, *args):
		self.plot_effect.uniforms['center_x'] = self.center_x
		self.plot_effect.uniforms['center_y'] = self.center_y


class TestApp(App):
	def build(self):
		return Plot()

if __name__ == '__main__':
	TestApp().run()