ModernGL with QOpenGLWidget isn't rendering

? Offline

Hi all. I am so stumped on why the triangle is not rendering. My shaders are correct, I set up the VBO and VAOs correctly, its just not rendering anything for some reason.

import sys
import moderngl as GL
import numpy
from PyQt6.QtGui import *
from PyQt6.QtWidgets import *
from PyQt6.QtCore import *
from PyQt6.QtOpenGLWidgets import *


class Main(QOpenGLWidget):
    def __init__(self, parent=None):
        super().__init__(parent)

    def initializeGL(self):
        # Set up the OpenGL context using moderngl
        self.ctx = GL.create_context()
        self.ctx.clear(0, 0, 0)

        # Define shaders with error checking
        vertex_shader_code = '''
        #version 330 core

        in vec3 in_vert;

        void main() {
            gl_Position = vec4(in_vert, 1.0);
        }
        '''
        fragment_shader_code = '''
        #version 330 core

        out vec4 fragColor;

        uniform vec4 color;

        void main() {
            fragColor = color;
        }
        '''

        # Compile shaders and program
        self.program = self.ctx.program(
            vertex_shader=vertex_shader_code,
            fragment_shader=fragment_shader_code
        )

        # Check for any shader compilation issues
        if not self.program:
            print("Shader program failed to compile.")
            return

        # Define triangle vertices (in normalized device coordinates)
        self.vertices = numpy.array([
            0.0, 0.5, 0.0,  # Top vertex
            -0.5, -0.5, 0.0,  # Bottom-left vertex
            0.5, -0.5, 0.0  # Bottom-right vertex
        ], dtype='f4')

        # Create the buffer for the vertices
        self.vbo = self.ctx.buffer(self.vertices)

        # Create vertex array object (VAO)
        self.vao = self.ctx.simple_vertex_array(self.program, self.vbo, 'in_vert')

        # Set the uniform color (Red in this case)
        self.program['color'].value = (1.0, 1.0, 1.0, 1.0)  # Red

    def resizeGL(self, w, h):
        self.ctx.viewport = (0, 0, w, h)
        self.update()

    def paintGL(self):
        # Clear the screen
        self.ctx.clear(0.0, 0.0, 0.0)

        # Draw the triangle
        self.vao.render()


if __name__ == '__main__':
    app = QApplication([])

    win = Main()
    win.resize(800, 600)
    win.show()

    sys.exit(app.exec())

I would like to add that if I remove self.ctx.clear(0.0, 0.0, 0.0) from the paintGL() method, it renders the vertices correctly. I can't do this though (obviously because I need to clear each frame before rendering)

SGaist

From a quick look at the code of QOpenGLWidget, I don't think you can.

Do you really need QOpenGLWidget ? Maybe QWindow might do what you want.

SGaist

Hi,

The thing that is strange here is your context creation. AFAIK, QOpenGLWidget already has a context that will be made current when paintGL is called.

? Offline

@SGaist How could I prevent QOpenGLWidget from creating its own context? Or is there another widget that can render an OpenGL context in PyQt6?

All of this works in PyQt5 with QGLWidget.

SGaist

From a quick look at the code of QOpenGLWidget, I don't think you can.

Do you really need QOpenGLWidget ? Maybe QWindow might do what you want.

? Offline

@SGaist said in ModernGL with QOpenGLWidget isn't rendering:

Do you really need QOpenGLWidget ? Maybe QWindow might do what you want.

Any examples for QWindow OpenGL rendering? I don’t absolutely need QOpenGLWidget

jsulm

@ktechhydle If you enter "qt6 QWindow OpenGL" in Google first result is: https://doc.qt.io/qt-6/qtopengl-openglwindow-example.html

Hexplivyus

Hi,

For those looking for a functional answer:

import sys
import moderngl as GL
import numpy
from PyQt6.QtWidgets import QApplication
from PyQt6.QtOpenGLWidgets import QOpenGLWidget


class Main(QOpenGLWidget):
    def __init__(self, parent=None):
        super().__init__(parent)

    def initializeGL(self):
        # Set up the OpenGL context using moderngl
        self.ctx = GL.create_context()
        self.ctx.clear(0, 0, 0)

        # Define shaders with error checking
        vertex_shader_code = '''
        #version 330 core

        in vec3 in_vert;

        void main() {
            gl_Position = vec4(in_vert, 1.0);
        }
        '''
        fragment_shader_code = '''
        #version 330 core

        out vec4 fragColor;

        uniform vec4 color;

        void main() {
            fragColor = color;
        }
        '''

        # Compile shaders and program
        self.program = self.ctx.program(
            vertex_shader=vertex_shader_code,
            fragment_shader=fragment_shader_code
        )

        # Check for any shader compilation issues
        if not self.program:
            print("Shader program failed to compile.")
            return

        # Define triangle vertices (in normalized device coordinates)
        self.vertices = numpy.array([
            0.0, 0.5, 0.0,  # Top vertex
            -0.5, -0.5, 0.0,  # Bottom-left vertex
            0.5, -0.5, 0.0  # Bottom-right vertex
        ], dtype='f4')

        # Create the buffer for the vertices
        self.vbo = self.ctx.buffer(self.vertices)

        # Create vertex array object (VAO)
        self.vao = self.ctx.simple_vertex_array(self.program, self.vbo, 'in_vert')

        # Set the uniform color (Red in this case)
        self.program['color'].value = (1.0, 0.0, 0.0, 1.0)  # Red # EDITED: 1.0, 1.0, 1.0 is white.

    def resizeGL(self, w, h):
        # EDITED: Detect framebuffer again after resize.
        # To be fair: Claude AI gave me this solution.
        fbo = self.ctx.detect_framebuffer()
        fbo.use()
        self.ctx.viewport = (0, 0, w, h)

    def paintGL(self):
        # Clear the screen
        self.ctx.clear(0.0, 0.0, 0.0)

        # Draw the triangle
        self.vao.render()


if __name__ == '__main__':
    app = QApplication([])

    win = Main()
    win.resize(800, 600)
    win.show()

    sys.exit(app.exec())

webhan

dont use self.ctx.clear in paintGL because its can make your shader into black fill, so you just write ctx.clear in initializeGL

like this

    def initializeGL(self):
        self.ctx = moderngl.create_context()
        self.ctx.clear(0,0,0,0)