[SOLVED] Drawing a triangle using PyQt5 and OpenGL (rewriting the Qt C++ example)

My current PyQt5 example does not show a window and does not give me any error messages.

This is Qt C++ example that works very good. I want to use QOpenGLBuffer in my PyQt5 code.

main.cpp

Code:

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#include <QApplication>
#include <QOpenGLWidget>
#include <QOpenGLShaderProgram>
#include <QOpenGLBuffer>
 
class Widget : public QOpenGLWidget {
    Q_OBJECT
public:
    Widget(QWidget *parent = nullptr) : QOpenGLWidget(parent) { }
private:
    QOpenGLShaderProgram m_program;
    QOpenGLBuffer m_vertPosBuffer;
 
    void initializeGL() override {
        glClearColor(0.5f, 0.8f, 0.7f, 1.f);
        resize(400, 500);
        const char *vertShaderSrc =
                "attribute vec3 aPosition;"
                "void main()"
                "{"
                "    gl_Position = vec4(aPosition, 1.0);"
                "}";
        const char *fragShaderSrc =
                "void main()"
                "{"
                "    gl_FragColor = vec4(0.5, 0.2, 0.9, 1.0);"
                "}";
        m_program.addShaderFromSourceCode(QOpenGLShader::Vertex, vertShaderSrc);
        m_program.addShaderFromSourceCode(QOpenGLShader::Fragment, fragShaderSrc);
        m_program.link();
        m_program.bind();
        float vertPositions[] = {
            -0.5f, -0.5f, 0.f,
            0.5f, -0.5f, 0.f,
            0.f, 0.5f, 0.f
        };
        m_vertPosBuffer.create();
        m_vertPosBuffer.bind();
        m_vertPosBuffer.allocate(vertPositions, sizeof(vertPositions));
        m_program.bindAttributeLocation("aPosition", 0);
        m_program.setAttributeBuffer(0, GL_FLOAT, 0, 3);
        m_program.enableAttributeArray(0);
    }
    void paintGL() override {
        glClear(GL_COLOR_BUFFER_BIT);
        glDrawArrays(GL_TRIANGLES, 0, 3);
    }
    void resizeGL(int w, int h) override {
        glViewport(0, 0, w, h);
    }
};
 
#include "main.moc"
 
int main(int argc, char *argv[]) {
    QApplication a(argc, argv);
    Widget w;
    w.show();
    return a.exec();
}

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This is my trying to rewrite the code above to PyQt5. As you can see I want to rewrite it very close to Qt C++. I want to have two very similar example. But this code does not show a windows and does not show any error messages.

main.py

Code:

---

import sys
import numpy as np
from OpenGL import GL as gl
from PyQt5.QtWidgets import QOpenGLWidget, QApplication
from PyQt5.QtGui import (QOpenGLBuffer, QOpenGLShaderProgram,
    QOpenGLShader)
from PyQt5.QtCore import Qt
 
class OpenGLWidget(QOpenGLWidget):
    def __init__(self):
        super().__init__()
        self.setWindowTitle("Triangle, PyQt5, OpenGL ES 2.0")
        self.resize(300, 300)
    def initializeGL(self):
        gl.glClearColor(0.5, 0.8, 0.7, 1.0)
        vertShaderSrc = """
            attribute vec3 aPosition;
            void main()
            {
                gl_Position = vec4(aPosition, 1.0);
            }
        """
        fragShaderSrc = """
            void main()
            {
                gl_FragColor = vec4(0.5, 0.2, 0.9, 1.0);
            }
        """
        program = QOpenGLShaderProgram()
        program.addShaderFromSourceCode(QOpenGLShader.Vertex, vertShaderSrc)
        program.addShaderFromSourceCode(QOpenGLShader.Fragment, fragShaderSrc)
        program.link()
        program.bind()
        vertPositions = np.array([
            -0.5, -0.5, 0.0,
            0.5, -0.5, 0.0,
            0.0, 0.5, 0.0], dtype=np.float32)
        vertPosBuffer = QOpenGLBuffer()
        vertPosBuffer.create()
        vertPosBuffer.bind()
        vertPosBuffer.allocate(vertPositions, len(vertPositions) * 4)
        program.bindAttributeLocation("aPosition", 0)
        program.setAttributeBuffer(0, gl.GL_FLOAT, 0, 3)
        program.enableAttributeArray(0)
 
    def paintGL(self):
        gl.glClear(gl.GL_COLOR_BUFFER_BIT)
        gl.glDrawArrays(gl.GL_TRIANGLES, 0, 3)
 
def main():
    QApplication.setAttribute(Qt.AA_UseDesktopOpenGL)
    a = QApplication(sys.argv)
    w = OpenGLWidget()
    w.show()
    sys.exit(a.exec_())
 
if __name__ == "__main__":
    main()

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Added after 1 14 minutes:

eyllanesc solved my problem here: https://stackoverflow.com/questions/...15511#64915511

Quote:

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The problem is that the QOpenGLBuffer is a local variable that is destroyed instantly, whereas in C++ QOpenGLBuffer is an attribute of the class. The solution is to change vertPosBuffer to self.vertPosBuffer

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