{
  "cells": [
    {
      "cell_type": "code",
      "execution_count": null,
      "metadata": {
        "collapsed": false
      },
      "outputs": [],
      "source": [
        "%gui qt"
      ]
    },
    {
      "cell_type": "markdown",
      "metadata": {},
      "source": [
        "\n# Use a Geometry Shader\n\nSimple geometry shader: Takes one point as input emits one triangle as output.\n\nNOTE: This example is currently not processed in CI.\n"
      ]
    },
    {
      "cell_type": "code",
      "execution_count": null,
      "metadata": {
        "collapsed": false
      },
      "outputs": [],
      "source": [
        "import numpy as np\nfrom vispy import gloo\nfrom vispy import app\n\n# geometry shaders require full OpenGL namespace provided by PyOpenGL\ngloo.gl.use_gl('gl+')\n\n\nposition = np.random.normal(loc=0, scale=0.3, size=(1000, 2)).astype('float32')\n\n\nVERT_SHADER = \"\"\"\n#version 330\n\nin vec2 a_position;\n\nvoid main (void) {\n    gl_Position = vec4(a_position, 0, 1);\n    gl_PointSize = 3.0;\n}\n\"\"\"\n\n\nGEOM_SHADER = \"\"\"\n#version 330\n\nlayout (points) in;\nlayout (triangle_strip, max_vertices=3) out;\n\nvoid main(void) {\n    vec4 p = gl_in[0].gl_Position;\n    \n    gl_Position = p;\n    EmitVertex();\n    gl_Position = p + vec4(0.06, 0.03, 0, 0);\n    EmitVertex();\n    gl_Position = p + vec4(0.03, 0.06, 0, 0);\n    EmitVertex();\n    EndPrimitive();\n}\n\"\"\"\n\n\nFRAG_SHADER = \"\"\"\n#version 330\n\nout vec4 frag_color;\n\nvoid main()\n{\n    frag_color = vec4(0,0,0,0.5);\n}\n\"\"\"\n\n\nclass Canvas(app.Canvas):\n    def __init__(self):\n        app.Canvas.__init__(self, keys='interactive', size=(400, 400))\n        self.program = gloo.Program()\n        self.program.set_shaders(vert=VERT_SHADER, geom=GEOM_SHADER,\n                                 frag=FRAG_SHADER)\n        self.program['a_position'] = gloo.VertexBuffer(position)\n        gloo.set_viewport(0, 0, self.physical_size[0], self.physical_size[1])\n        self.context.set_clear_color('white')\n        self.context.set_state('translucent', cull_face=False,\n                               depth_test=False)\n        self.show()\n\n    def on_resize(self, event):\n        gloo.set_viewport(0, 0, event.physical_size[0], event.physical_size[1])\n\n    def on_draw(self, event):\n        self.context.clear()\n        self.program.draw('points')\n\n\nif __name__ == '__main__':\n    canvas = Canvas()\n    app.run()"
      ]
    }
  ],
  "metadata": {
    "kernelspec": {
      "display_name": "Python 3",
      "language": "python",
      "name": "python3"
    },
    "language_info": {
      "codemirror_mode": {
        "name": "ipython",
        "version": 3
      },
      "file_extension": ".py",
      "mimetype": "text/x-python",
      "name": "python",
      "nbconvert_exporter": "python",
      "pygments_lexer": "ipython3",
      "version": "3.9.20"
    }
  },
  "nbformat": 4,
  "nbformat_minor": 0
}