Note

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# 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()

Total running time of the script: ( 0 minutes 0.139 seconds)

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