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"""Transliteration of https://open.gl/feedback into Python"""
from __future__ import print_function
import pygamegltest
from OpenGL.GL import *
from OpenGL.GL import shaders
vertex_shader = """#version 150 core
in float inValue;
out float outValue;
void main() {
outValue = sqrt(inValue);
}
"""
@pygamegltest.pygametest(name="Geometry Shader Test")
def main():
program = shaders.compileProgram(
shaders.compileShader([vertex_shader], GL_VERTEX_SHADER),
)
buff = ctypes.c_char_p(b"outValue")
c_text = ctypes.cast(ctypes.pointer(buff), ctypes.POINTER(ctypes.POINTER(GLchar)))
# modifies the state in the linking of the program
glTransformFeedbackVaryings(program, 1, c_text, GL_INTERLEAVED_ATTRIBS)
# so have to re-link
glLinkProgram(program)
glUseProgram(program)
vao = glGenVertexArrays(1)
glBindVertexArray(vao)
data = (GLfloat * 5)(1.0, 2.0, 3.0, 4.0, 5.0)
vbo = glGenBuffers(1)
glBindBuffer(GL_ARRAY_BUFFER, vbo)
glBufferData(GL_ARRAY_BUFFER, ctypes.sizeof(data), data, GL_STATIC_DRAW)
inputAttrib = glGetAttribLocation(program, "inValue")
glEnableVertexAttribArray(inputAttrib)
# Note the need to cast 0 to a GLvoidp here!
glVertexAttribPointer(inputAttrib, 1, GL_FLOAT, GL_FALSE, 0, GLvoidp(0))
tbo = glGenBuffers(1)
glBindBuffer(GL_ARRAY_BUFFER, tbo)
glBufferData(GL_ARRAY_BUFFER, ctypes.sizeof(data), None, GL_STATIC_READ)
glEnable(GL_RASTERIZER_DISCARD)
glBindBufferBase(GL_TRANSFORM_FEEDBACK_BUFFER, 0, tbo)
glBeginTransformFeedback(GL_POINTS)
glDrawArrays(GL_POINTS, 0, len(data))
glEndTransformFeedback()
glDisable(GL_RASTERIZER_DISCARD)
glFlush()
feedback = (GLfloat * len(data))()
glGetBufferSubData(
GL_TRANSFORM_FEEDBACK_BUFFER, 0, ctypes.sizeof(feedback), feedback
)
for value in feedback:
print(value)
print('OK')
if __name__ == "__main__":
main()
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