QOpenGLWidget: Porting code from GLUT showing a webcam feed

dboth

Hello,

I am writing an application that shows the user's webcam video feed in a PyQT5 window. Using a QLabel and updating the label's pixmap for every frame is to slow due to the target device's performance.

I therefore tried to gain some speed by using OpenGL to display the video frames as 2D texture on a rectangle. I found this example on Stackoverflow that works using GLUT. However, I fail to port the code from using GLUT to a QOpenGLWidget.

For the init and reshape functions in GLUT it seems logical to me that they correspond to the initializeGL and resizeGL functions in QT. But where in the QOpenGLWidget lifecycle do the display and idle functions belong? Executing them inside paintGL shows no effect. The current code does not crash, but the widget stays black.

What is the right way to do this?

I am glad for any help or suggestion.

#!/usr/bin/env python
import sys, time
import cv2
import numpy as np
from PyQt5.QtCore import *
from PyQt5.QtGui import *
from PyQt5.QtWidgets import *


class GLWidget(QOpenGLWidget):
    def __init__(self, parent=None, width=1280, height=720):
        self.parent = parent
        self.width = width
        self.height = height
        QOpenGLWidget.__init__(self, parent)

    def sizeHint(self):
        return QSize(self.width,self.height)

    def setImage(self,image):
        self.image = np.flipud(image).tobytes()
        self._idle()

    def initializeGL(self):
        version_profile = QOpenGLVersionProfile()
        version_profile.setVersion(2,0)
        self.gl = self.context().versionFunctions(version_profile)
        self.gl.glClearColor(0.0, 0.0, 0.0, 1.0) 
        self.setImage(np.zeros((self.width, self.height,3)))

    def _idle(self):
        self.gl.glTexImage2D(self.gl.GL_TEXTURE_2D, 
            0, 
            self.gl.GL_RGB, 
            self.width,self.height,
            0,
            self.gl.GL_RGB, 
            self.gl.GL_UNSIGNED_BYTE, 
            self.image)
        self.update()

    def _display(self):
        self.gl.glClear(self.gl.GL_COLOR_BUFFER_BIT | self.gl.GL_DEPTH_BUFFER_BIT)
        self.gl.glEnable(self.gl.GL_TEXTURE_2D)
        self.gl.glTexParameterf(self.gl.GL_TEXTURE_2D, self.gl.GL_TEXTURE_MIN_FILTER, self.gl.GL_NEAREST)
        
        self.gl.glMatrixMode(self.gl.GL_PROJECTION)
        self.gl.glLoadIdentity()
        self.gl.glOrtho(0, self.width, 0, self.height,-1,1)
        
        self.gl.glMatrixMode(self.gl.GL_MODELVIEW)
        self.gl.glLoadIdentity()    

        self.gl.glBegin(self.gl.GL_QUADS)
        self.gl.glTexCoord2f(0.0, 0.0)
        self.gl.glVertex2f(0.0, 0.0)
        self.gl.glTexCoord2f(1.0, 0.0)
        self.gl.glVertex2f(self.width, 0.0)
        self.gl.glTexCoord2f(1.0, 1.0)
        self.gl.glVertex2f(self.width, self.height)
        self.gl.glTexCoord2f(0.0, 1.0)
        self.gl.glVertex2f(0.0, self.height)
        self.gl.glEnd()
        self.gl.glFlush()

    def resizeGL(self, w, h):
        if h == 0:
            h = 1

        self.gl.glViewport(0, 0, w, h)
        self.gl.glMatrixMode(self.gl.GL_PROJECTION)

        self.gl.glLoadIdentity()
        
        if w <= h:
            self.gl.glOrtho(-1, 1, -1*h/w, h/w, -1, 1)
        else:
            self.gl.glOrtho(-1*w/h, w/h, -1, 1, -1, 1)

        self.gl.glMatrixMode(self.gl.GL_MODELVIEW)
        self.gl.glLoadIdentity()

    def paintGL(self):
        self._display()
      

class VideoThread(QThread):
    change_image_signal = pyqtSignal(np.ndarray)

    def __init__(self):
        super().__init__()
        self._run_flag = True

    def run(self):
        capture = cv2.VideoCapture(0)
        capture.set(cv2.CAP_PROP_BUFFERSIZE,3)
        while self._run_flag:
            _, frame = capture.read()
            frame = cv2.cvtColor(frame, cv2.COLOR_BGR2RGB)
            self.change_image_signal.emit(frame)
            time.sleep(0.4)
        capture.release()

    def stop(self):
        self._run_flag = False
        self.wait()


class MainUI(QWidget):

    def __init__(self):
        QWidget.__init__(self)
        self.video_size = QSize(394,292)
        self.setup_ui()
        self.setup_camera()

    def setup_ui(self):
        self.video_widget = GLWidget(self,self.video_size.width(),self.video_size.height())
        self.main_layout = QGridLayout()
        self.main_layout.addWidget(self.video_widget,0,0)
        self.setLayout(self.main_layout)

    def closeEvent(self, event):
        self.thread.stop()
        event.accept()

    def setup_camera(self):
        self.thread = VideoThread()
        self.thread.change_image_signal.connect(self.display_video_stream)
        self.thread.start()

    @pyqtSlot(np.ndarray)
    def display_video_stream(self,image):
        self.video_widget.setImage(image)

if __name__ == "__main__":
    app = QApplication(sys.argv)
    win = MainUI()
    win.show()
    sys.exit(app.exec())

SGaist

Hi and welcome to devnet,

First, out of curiosity, any reasons for not using Qt Multimedia's camera support ?