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      "source": [
        "%gui qt"
      ]
    },
    {
      "cell_type": "markdown",
      "metadata": {},
      "source": [
        "\n# Animate a 2D function\n\nIllustrate how to plot a 2D function (an image) y=f(x,y) on the GPU.\n"
      ]
    },
    {
      "cell_type": "code",
      "execution_count": null,
      "metadata": {
        "collapsed": false
      },
      "outputs": [],
      "source": [
        "from vispy import app, gloo\n\nvertex = \"\"\"\nattribute vec2 a_position;\nvarying vec2 v_position;\nvoid main()\n{\n    gl_Position = vec4(a_position, 0.0, 1.0);\n    v_position = a_position;\n}\n\"\"\"\n\nfragment = \"\"\"\n#include \"math/constants.glsl\"\n//const float M_PI = 3.14159265358979323846;\nuniform float u_time;\nvarying vec2 v_position;\n\n/**********************************************************\nSpecify the parameters here.\n**********************************************************/\nconst float z_offset = 1.;  // (z+z_offset)/z_max should be in [0,1]\nconst float z_max = 2.;\nconst float x_scale = 5.;  // x is between -x_scale and +x_scale\nconst float y_scale = 5.; // y is between -y_scale and +y_scale\nconst float t_scale = 5.; // scale for the time\n/*********************************************************/\n\nfloat f(float x, float y, float t) {\n\n    // x is in [-x_scale, +x_scale]\n    // y is in [-y_scale, +y_scale]\n    // t is in [0, +oo)\n\n    /**********************************************************\n    Write your function below.\n    **********************************************************/\n\n    float k = .25*cos(t);\n    return (cos(x)+k)*(sin(y)-k);\n\n    /*********************************************************/\n\n}\n\nvec4 jet(float x) {\n    vec3 a, b;\n    float c;\n    if (x < 0.34) {\n        a = vec3(0, 0, 0.5);\n        b = vec3(0, 0.8, 0.95);\n        c = (x - 0.0) / (0.34 - 0.0);\n    } else if (x < 0.64) {\n        a = vec3(0, 0.8, 0.95);\n        b = vec3(0.85, 1, 0.04);\n        c = (x - 0.34) / (0.64 - 0.34);\n    } else if (x < 0.89) {\n        a = vec3(0.85, 1, 0.04);\n        b = vec3(0.96, 0.7, 0);\n        c = (x - 0.64) / (0.89 - 0.64);\n    } else {\n        a = vec3(0.96, 0.7, 0);\n        b = vec3(0.5, 0, 0);\n        c = (x - 0.89) / (1.0 - 0.89);\n    }\n    return vec4(mix(a, b, c), 1.0);\n}\n\nvoid main() {\n    vec2 pos = v_position;\n    float z = f(x_scale * pos.x, y_scale * pos.y, t_scale * u_time);\n    gl_FragColor = jet((z + z_offset) / (z_max));\n}\n\"\"\"\n\n\nclass Canvas(app.Canvas):\n    def __init__(self):\n        app.Canvas.__init__(self, position=(300, 100),\n                            size=(800, 800), keys='interactive')\n\n        self.program = gloo.Program(vertex, fragment)\n        self.program['a_position'] = [(-1., -1.), (-1., +1.),\n                                      (+1., -1.), (+1., +1.)]\n\n        self.program['u_time'] = 0.0\n        self.timer = app.Timer('auto', connect=self.on_timer, start=True)\n\n        self.show()\n\n    def on_timer(self, event):\n        self.program['u_time'] = event.elapsed\n        self.update()\n\n    def on_resize(self, event):\n        width, height = event.physical_size\n        gloo.set_viewport(0, 0, width, height)\n\n    def on_draw(self, event):\n        self.program.draw('triangle_strip')\n\n\nif __name__ == '__main__':\n    canvas = Canvas()\n    app.run()"
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