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"""
Render using empty Vertexbuffer.
Renders 100 triangels emitted by a geometry shaders.
In addition we test if instancing is working passing gl_InstanceID from the vertex shader.
"""
import moderngl
from _example import Example
class HelloWorld(Example):
gl_version = (3, 3)
title = "Empty Vertexbuffer"
def __init__(self, **kwargs):
super().__init__(**kwargs)
self.prog = self.ctx.program(
vertex_shader='''
#version 330
out int inst;
void main() {
inst = gl_InstanceID;
}
''',
geometry_shader='''
#version 330
layout (points) in;
layout (triangle_strip, max_vertices = 3) out;
in int inst[1];
void main() {
float x = float(gl_PrimitiveIDIn / 10) / 9 - 0.5 + inst[0] / 20.0;
float y = float(gl_PrimitiveIDIn % 10) / 9 - 0.5 + inst[0] / 20.0;
gl_Position = vec4(x - 0.03, y - 0.03, 0.0, 1.0);
EmitVertex();
gl_Position = vec4(x + 0.03, y - 0.03, 0.0, 1.0);
EmitVertex();
gl_Position = vec4(x, y + 0.03, 0.0, 1.0);
EmitVertex();
EndPrimitive();
}
''',
fragment_shader='''
#version 330
out vec4 f_color;
void main() {
f_color = vec4(0.3, 0.5, 1.0, 1.0);
}
''',
)
self.vao = self.ctx.vertex_array(self.prog, [])
def render(self, time, frame_time):
self.ctx.clear(1.0, 1.0, 1.0)
self.vao.render(mode=moderngl.POINTS, vertices=100, instances=2)
if __name__ == '__main__':
HelloWorld.run()
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