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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)
if __name__ == "__main__":
main()
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