Use a Geometry Shader

Simple geometry shader: Takes one point as input emits one triangle as output.

NOTE: This example is currently not processed in CI.

import numpy as np
from vispy import gloo
from vispy import app

# geometry shaders require full OpenGL namespace provided by PyOpenGL
gloo.gl.use_gl('gl+')


position = np.random.normal(loc=0, scale=0.3, size=(1000, 2)).astype('float32')


VERT_SHADER = """
#version 330

in vec2 a_position;

void main (void) {
    gl_Position = vec4(a_position, 0, 1);
    gl_PointSize = 3.0;
}
"""


GEOM_SHADER = """
#version 330

layout (points) in;
layout (triangle_strip, max_vertices=3) out;

void main(void) {
    vec4 p = gl_in[0].gl_Position;

    gl_Position = p;
    EmitVertex();
    gl_Position = p + vec4(0.06, 0.03, 0, 0);
    EmitVertex();
    gl_Position = p + vec4(0.03, 0.06, 0, 0);
    EmitVertex();
    EndPrimitive();
}
"""


FRAG_SHADER = """
#version 330

out vec4 frag_color;

void main()
{
    frag_color = vec4(0,0,0,0.5);
}
"""


class Canvas(app.Canvas):
    def __init__(self):
        app.Canvas.__init__(self, keys='interactive', size=(400, 400))
        self.program = gloo.Program()
        self.program.set_shaders(vert=VERT_SHADER, geom=GEOM_SHADER,
                                 frag=FRAG_SHADER)
        self.program['a_position'] = gloo.VertexBuffer(position)
        gloo.set_viewport(0, 0, self.physical_size[0], self.physical_size[1])
        self.context.set_clear_color('white')
        self.context.set_state('translucent', cull_face=False,
                               depth_test=False)
        self.show()

    def on_resize(self, event):
        gloo.set_viewport(0, 0, event.physical_size[0], event.physical_size[1])

    def on_draw(self, event):
        self.context.clear()
        self.program.draw('points')


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