Example demonstrating simulation of fireworks using point sprites

(adapted from the “OpenGL ES 2.0 Programming Guide”) This example demonstrates a series of explosions that last one second. The visualization during the explosion is highly optimized using a Vertex Buffer Object (VBO). After each explosion, vertex data for the next explosion are calculated, such that each explostion is unique.

import numpy as np

from vispy import app
from vispy.gloo import gl


vertex_code = """
#version 120

uniform float time;
uniform vec3 center;
attribute float lifetime;
attribute vec3 start;
attribute vec3 end;
varying float v_lifetime;
void main () {
    if (time < lifetime) {
        gl_Position.xyz = start + (time * end) + center;
        gl_Position.w = 1.0;
        gl_Position.y -= 1.5 * time * time;
    } else {
        gl_Position = vec4(-1000, -1000, 0, 0);
    }
    v_lifetime = clamp(1.0 - (time / lifetime), 0.0, 1.0);
    gl_PointSize = (v_lifetime * v_lifetime) * 40.0;
}
"""

fragment_code = """
#version 120

uniform vec4 color;
varying float v_lifetime;
void main()
{
    float d = 1 - length(gl_PointCoord - vec2(.5,.5)) / (sqrt(2)/2);
    gl_FragColor = d*color;
    gl_FragColor.a = d;
    gl_FragColor.a *= v_lifetime;
}
"""


class Canvas(app.Canvas):
    def __init__(self):
        app.Canvas.__init__(self, size=(800, 600), title='GL Fireworks',
                            keys='interactive')

    def on_initialize(self, event):
        # Build & activate program
        self.program = gl.glCreateProgram()
        vertex = gl.glCreateShader(gl.GL_VERTEX_SHADER)
        fragment = gl.glCreateShader(gl.GL_FRAGMENT_SHADER)
        gl.glShaderSource(vertex, vertex_code)
        gl.glShaderSource(fragment, fragment_code)
        gl.glCompileShader(vertex)
        gl.glCompileShader(fragment)
        gl.glAttachShader(self.program, vertex)
        gl.glAttachShader(self.program, fragment)
        gl.glLinkProgram(self.program)
        gl.glDetachShader(self.program, vertex)
        gl.glDetachShader(self.program, fragment)
        gl.glUseProgram(self.program)

        # Build vertex buffer
        n = 10000
        self.data = np.zeros(n, dtype=[('lifetime', np.float32),
                                       ('start', np.float32, 3),
                                       ('end', np.float32, 3)])
        vbuffer = gl.glCreateBuffer()
        gl.glBindBuffer(gl.GL_ARRAY_BUFFER, vbuffer)
        gl.glBufferData(gl.GL_ARRAY_BUFFER, self.data, gl.GL_DYNAMIC_DRAW)

        # Bind buffer attributes
        stride = self.data.strides[0]

        offset = 0
        loc = gl.glGetAttribLocation(self.program, "lifetime")
        gl.glEnableVertexAttribArray(loc)
        gl.glVertexAttribPointer(loc, 1, gl.GL_FLOAT, False, stride, offset)

        offset = self.data.dtype["lifetime"].itemsize
        loc = gl.glGetAttribLocation(self.program, "start")
        gl.glEnableVertexAttribArray(loc)
        gl.glVertexAttribPointer(loc, 3, gl.GL_FLOAT, False, stride, offset)

        offset = self.data.dtype["start"].itemsize
        loc = gl.glGetAttribLocation(self.program, "end")
        gl.glEnableVertexAttribArray(loc)
        gl.glVertexAttribPointer(loc, 3, gl.GL_FLOAT, False, stride, offset)

        # OpenGL initalization
        self.elapsed_time = 0
        gl.glClearColor(0, 0, 0, 1)
        gl.glDisable(gl.GL_DEPTH_TEST)
        gl.glEnable(gl.GL_BLEND)
        gl.glBlendFunc(gl.GL_SRC_ALPHA, gl.GL_ONE)
        gl.glEnable(34370)  # gl.GL_VERTEX_PROGRAM_POINT_SIZE
        gl.glEnable(34913)  # gl.GL_POINT_SPRITE
        gl.glViewport(0, 0, *self.physical_size)
        self.new_explosion()
        self.timer = app.Timer('auto', self.on_timer, start=True)

    def on_draw(self, event):
        gl.glClear(gl.GL_COLOR_BUFFER_BIT | gl.GL_DEPTH_BUFFER_BIT)
        gl.glDrawArrays(gl.GL_POINTS, 0, len(self.data))

    def on_resize(self, event):
        gl.glViewport(0, 0, *event.physical_size)

    def on_timer(self, event):
        self.elapsed_time += 1. / 60.
        if self.elapsed_time > 1.5:
            self.new_explosion()
            self.elapsed_time = 0.0

        loc = gl.glGetUniformLocation(self.program, "time")
        gl.glUniform1f(loc, self.elapsed_time)
        self.update()

    def new_explosion(self):
        n = len(self.data)
        color = np.random.uniform(0.1, 0.9, 4).astype(np.float32)
        color[3] = 1.0 / n ** 0.08
        loc = gl.glGetUniformLocation(self.program, "color")
        gl.glUniform4f(loc, *color)

        center = np.random.uniform(-0.5, 0.5, 3)
        loc = gl.glGetUniformLocation(self.program, "center")
        gl.glUniform3f(loc, *center)

        self.data['lifetime'] = np.random.normal(2.0, 0.5, (n,))
        self.data['start'] = np.random.normal(0.0, 0.2, (n, 3))
        self.data['end'] = np.random.normal(0.0, 1.2, (n, 3))
        gl.glBufferData(gl.GL_ARRAY_BUFFER, self.data, gl.GL_DYNAMIC_DRAW)

if __name__ == '__main__':
    c = Canvas()
    c.show()
    app.run()