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      "source": [
        "%gui qt"
      ]
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      "source": [
        "\n# Custom Visual for instanced rendering of a colored quad\n\n# this example is based on the tutorial: T01_basic_visual.py\n"
      ]
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    {
      "cell_type": "code",
      "execution_count": null,
      "metadata": {
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      },
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      "source": [
        "from vispy import app, gloo, visuals, scene, use\nimport numpy as np\n\n# full gl+ context is required for instanced rendering\nuse(gl='gl+')\n\n\nvertex_shader = \"\"\"\n// both these attributes will be defined on an instance basis (not per vertex)\nattribute vec2 shift;\nattribute vec4 color;\n\nvarying vec4 v_color;\nvoid main() {\n    v_color = color;\n    gl_Position = $transform(vec4($position + shift, 0, 1));\n}\n\"\"\"\n\nfragment_shader = \"\"\"\nvarying vec4 v_color;\n\nvoid main() {\n  gl_FragColor = v_color;\n}\n\"\"\"\n\n\nclass InstancedRectVisual(visuals.Visual):\n    def __init__(self, x, y, w, h):\n        visuals.Visual.__init__(self, vertex_shader, fragment_shader)\n\n        # vertices for two triangles forming a rectangle\n        self.vbo = gloo.VertexBuffer(np.array([\n            [x, y], [x+w, y], [x+w, y+h],\n            [x, y], [x+w, y+h], [x, y+h]\n        ], dtype=np.float32))\n\n        self.shared_program.vert['position'] = self.vbo\n        self._draw_mode = 'triangles'\n\n        # create a vertex buffer with a divisor argument of 1. This means that the\n        # attribute value is set to the next element of the array every 1 instance.\n        # The length of the array multiplied by the divisor determines the number\n        # of instances\n        self.shifts = gloo.VertexBuffer(np.random.rand(100, 2).astype(np.float32) * 500, divisor=1)\n        self.shared_program['shift'] = self.shifts\n\n        # we can provide additional buffers with different divisors, as long as the\n        # amount of instances (length * divisor) is the same. In this case, we will change\n        # color every 5 instances\n        self.color = gloo.VertexBuffer(np.random.rand(20, 4).astype(np.float32), divisor=5)\n        self.shared_program['color'] = self.color\n\n    def _prepare_transforms(self, view):\n        view.view_program.vert['transform'] = view.get_transform()\n\n\n# create a visual node class to add it to the canvas\nInstancedRect = scene.visuals.create_visual_node(InstancedRectVisual)\n\ncanvas = scene.SceneCanvas(keys='interactive', show=True)\n\nrect = InstancedRect(0, 0, 20, 40, parent=canvas.scene)\n\nif __name__ == '__main__':\n    import sys\n    if sys.flags.interactive != 1:\n        app.run()"
      ]
    }
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