PyOpenGl Validation failure

Question

I am trying to create a simple scene with pyopengl, but I keep getting runtime error. I am using glfw for displaying opengl scene.

I am using python because I would like to include opengl in some other python projects.

I am on a macOS Mojave (10.14), Python 3.7

Error:

Traceback (most recent call last):
File "main.py", line 109, in <module>
main()
File "main.py", line 64, in main
shader = OpenGL.GL.shaders.compileProgram(s.vertex(), s.fragment())
File "slib/python3.7/site-packages/OpenGL/GL/shaders.py", line 196, in         
compileProgram
program.check_validate()
File "lib/python3.7/site-packages/OpenGL/GL/shaders.py", line 108, in 
check_validate
glGetProgramInfoLog( self ),
RuntimeError: Validation failure (0): b'Validation Failed: No vertex 
array object bound.\n'

Code:

import glfw
from OpenGL.GL import *
import OpenGL.GL.shaders
import numpy as np


def trikotnik():
    trikotnik = np.array([
        -0.5, -0.5, 0.0,
        0.5, -0.5, 0.0,
        0.0, 0.5, 0.0
    ], dtype=np.float32)
    return trikotnik


class Shaders:
    def __init__(self):
        pass

    def vertex(self):
        v = """
        #version 330
        in vec4 position; 
        void main() { 
            gl_Position = position; 
        } 
        """
        return OpenGL.GL.shaders.compileShader(v, GL_VERTEX_SHADER)

    def fragment(self):
        f = """
        #version 330
        out vec4 fragColor;
        void main() { 
            fragColor = vec4( 0, 1, 0, 1 );
        } 
        """
        return OpenGL.GL.shaders.compileShader(f, GL_FRAGMENT_SHADER)


def main():
    # Initialize the library
    if not glfw.init():
        return
    glfw.window_hint(glfw.CONTEXT_VERSION_MAJOR, 3)
    glfw.window_hint(glfw.CONTEXT_VERSION_MINOR, 2)
    glfw.window_hint(glfw.OPENGL_PROFILE, glfw.OPENGL_CORE_PROFILE)
    glfw.window_hint(glfw.OPENGL_FORWARD_COMPAT, GL_TRUE)

    # Create a windowed mode window and its OpenGL context
    window = glfw.create_window(640, 480, "Hello World", None, None)
    if not window:
        glfw.terminate()
        return

    # Make the window's context current
    glfw.make_context_current(window)

    # Creating shaders
    s = Shaders()
    shader = OpenGL.GL.shaders.compileProgram(s.vertex(), s.fragment())

    # Creating vertex buffer object on gpu
    VBO = glGenBuffers(1)
    glBindBuffer(GL_ARRAY_BUFFER, VBO)
    # Load data on array buffer...32 = size in bytes 9x4
    # GL_STATIC_DRAW: The vertex data will be uploaded once and drawn many times.
    glBufferData(GL_ARRAY_BUFFER, 32, trikotnik(), GL_STATIC_DRAW)
    glBindBuffer(GL_ARRAY_BUFFER, VBO)

    position = glGetAttribLocation(shader, "position")
    glVertexAttribPointer(
        position,  # attribute 0. No particular reason for 0, but must match the layout in the shader.
        3,  # size
        GL_FLOAT,  # type
        GL_FALSE,  # normalized
        0,  # stride
        None  # array buffer offset
    )
    glEnableVertexAttribArray(position)

    glUseProgram(shader)

    glClearColor(0, 107, 179, 1.0)

    # Loop until the user closes the window
    while not glfw.window_should_close(window):
        # Render here, e.g. using pyOpenGL

        # Clear color buffer
        glClear(GL_COLOR_BUFFER_BIT)

        # Draw
        glDrawArrays(GL_TRIANGLES, 0, 3)

        # Swap front and back buffers
        glfw.swap_buffers(window)
        # Poll for and process events
        glfw.poll_events()

    glfw.terminate()


if __name__ == "__main__":
    main()

I found this in source code:

validate (keyword only) -- if False, suppress automatic validation against current GL state. In advanced usage the validation can produce spurious errors. Note: this function is not really intended for advanced usage, if you're finding yourself specifying this flag you likely should be using your own shader management code.

I try to set it to False but I am still getting an error.

Answer 1

Either you use a Vertex Array Object or you switch to a compatibility profile context glfw.window_hint(glfw.OPENGL_PROFILE, glfw.OPENGL_COMPAT_PROFILE). In core profile you must have a named VAO, it is not optional.

Create and bind a VAO before specifying the array of vertex array data:

VAO = glGenVertexArrays(1)
glBindVertexArray(VAO)

glVertexAttribPointer(
    position,  # attribute 0. No particular reason for 0, but must match the layout in the shader.
    3,  # size
    GL_FLOAT,  # type
    GL_FALSE,  # normalized
    0,  # stride
    None  # array buffer offset
)
glEnableVertexAttribArray(position)