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"""
Shows transform feedback with geometry shaders were
the input and output primitive is different.
We have a list of points and emit triangle data to a buffer
It creates a quads per point using two triangles.
"""
import struct
from _example import Example
import moderngl
class GenerateData(Example):
title = "Transform Feedback Geometry shader"
gl_version = (3, 3)
def __init__(self, **kwargs):
super().__init__(**kwargs)
self.prog = self.ctx.program(
vertex_shader='''
#version 330
in vec3 in_vert;
void main() {
gl_Position = vec4(in_vert, 1.0);
}
''',
fragment_shader='''
#version 330
out vec4 f_color;
void main() {
f_color = vec4(1.0);
}
''',
)
# Transform program with geo shader
self.transform_prog = self.ctx.program(
vertex_shader='''
#version 330
void main() {
gl_Position = vec4(gl_VertexID/5.0 - 0.9, 0.0, 0.0, 1.0);
}
''',
geometry_shader="""
#version 330
layout(points) in;
layout(triangle_strip, max_vertices = 6) out;
out vec3 pos;
const float SIZE = 0.05;
void main() {
vec3 center = gl_in[0].gl_Position.xyz;
// First triangle
pos = center + vec3(-SIZE, SIZE, 0.0);
EmitVertex();
pos = center + vec3(-SIZE, -SIZE, 0.0);
EmitVertex();
pos = center + vec3(SIZE, SIZE, 0.0);
EmitVertex();
EndPrimitive();
// Second triangle
pos = center + vec3(SIZE, SIZE, 0.0);
EmitVertex();
pos = center + vec3(-SIZE, -SIZE, 0.0);
EmitVertex();
pos = center + vec3(SIZE, -SIZE, 0.0);
EmitVertex();
EndPrimitive();
}
""",
varyings=['pos'],
)
N = 10
self.buffer = self.ctx.buffer(reserve=N * 12 * 6) # N * 6 x vec3
self.transform_vao = self.ctx.vertex_array(self.transform_prog, [])
self.transform_vao.transform(self.buffer, mode=moderngl.POINTS, vertices=N)
self.vao = self.ctx.vertex_array(
self.prog,
[(self.buffer, '3f', 'in_vert')]
)
def render(self, time, frame_time):
self.wnd.clear()
self.vao.render(mode=moderngl.TRIANGLES)
if __name__ == '__main__':
GenerateData.run()
|
