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"""Transliteration of https://open.gl/feedback into Python"""
from __future__ import print_function
import pygamegltest
from OpenGL._bytes import as_8_bit
from OpenGL.GL import *
from OpenGL.GL import shaders
vertex_shader = """#version 150 core
in float inValue;
out float geoValue;
uniform float junk; // Just here for the introspection test
void main() {
geoValue = sqrt(inValue) + junk;
}
"""
geometry_shader = """#version 150 core
layout(points) in;
layout(triangle_strip, max_vertices = 3) out;
in float[] geoValue;
out float outValue;
void main() {
for (int i = 0; i < 3; i++) {
outValue = geoValue[0] + i;
EmitVertex();
}
EndPrimitive();
}
"""
@pygamegltest.pygametest(name="Geometry Shader Test")
def main():
program = shaders.compileProgram(
shaders.compileShader([vertex_shader], GL_VERTEX_SHADER),
shaders.compileShader([geometry_shader], GL_GEOMETRY_SHADER),
)
# test that we can describe the attributes in the shader
for i in range(glGetProgramiv(program, GL_ACTIVE_ATTRIBUTES)):
name, size, type = glGetActiveAttrib(program, i)
print('Atribute %s(%i) -> %s %s' % (name, i, size, type))
length, size, type, name = GLsizei(), GLint(), GLenum(), (GLchar * 8)()
glGetActiveAttrib(program, i, None, length, size, type, name)
assert length.value == len(name.value), (length.value, name.value)
assert type.value == 5126, type.value
for i in range(glGetProgramiv(program, GL_ACTIVE_UNIFORMS)):
name, size, type = glGetActiveUniform(program, i)
print('Uniform %s(%i) -> %s %s' % (name, i, size, type))
length, size, type, name = GLsizei(), GLint(), GLenum(), (GLchar * 5)()
glGetActiveUniform(program, i, 5, length, size, type, name)
assert length.value == len(name.value), (length.value, name.value)
assert type.value == 5126, type.value
buff = (ctypes.c_char_p * 1)(as_8_bit("outValue\000"))
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)
glVertexAttribPointer(inputAttrib, 1, GL_FLOAT, GL_FALSE, 0, 0)
tbo = glGenBuffers(1)
glBindBuffer(GL_ARRAY_BUFFER, tbo)
glBufferData(GL_ARRAY_BUFFER, ctypes.sizeof(data) * 3, None, GL_STATIC_READ)
glEnable(GL_RASTERIZER_DISCARD)
glBindBufferBase(GL_TRANSFORM_FEEDBACK_BUFFER, 0, tbo)
glBeginTransformFeedback(GL_TRIANGLES)
glDrawArrays(GL_POINTS, 0, 5)
glEndTransformFeedback()
glDisable(GL_RASTERIZER_DISCARD)
glFlush()
feedback = (GLfloat * 15)(*([0] * 15))
glGetBufferSubData(
GL_TRANSFORM_FEEDBACK_BUFFER, 0, ctypes.sizeof(feedback), feedback
)
for value in feedback:
print(value)
if __name__ == "__main__":
main()
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