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I would like to use Qt and PyOpenGL to do some real time plotting and learn a bit about OpenGL, but am having trouble even getting my initail test data to show up.
The idea is to store the x-coordinates and y-coordinates in different buffers since the x-coordinates will rarely change while the y-coordintates will change nearly every render. Unfortunately, having them in different buffers is giving me problems.
Right now I have no errors and nothing is showing up so I'm not sure where to go.
Here is what I have so far for the plotting class:
class GLWidget(QtOpenGL.QGLWidget):
def __init__(self, parent=None):
self.parent = parent
QtOpenGL.QGLWidget.__init__(self, parent)
self.current_position = 0
def initializeGL(self):
self.initGeometry()
self.vertex_code = """
#version 120
attribute vec4 color;
attribute float x_position;
attribute float y_position;
varying vec4 v_color;
void main()
{
gl_Position = vec4(x_position, y_position, 0.0, 1.0);
v_color = color;
} """
self.fragment_code = """
#version 120
varying vec4 v_color;
void main()
{
//gl_FragColor = v_color;
gl_FragColor = vec4(1,1,1,1);
} """
## Build and activate program
# Request program and shader slots from GPU
self.program = GL.glCreateProgram()
self.vertex = GL.glCreateShader(GL.GL_VERTEX_SHADER)
self.fragment = GL.glCreateShader(GL.GL_FRAGMENT_SHADER)
# Set shaders source
GL.glShaderSource(self.vertex, self.vertex_code)
GL.glShaderSource(self.fragment, self.fragment_code)
# Compile shaders
GL.glCompileShader(self.vertex)
GL.glCompileShader(self.fragment)
# Attach shader objects to the program
GL.glAttachShader(self.program, self.vertex)
GL.glAttachShader(self.program, self.fragment)
# Build program
GL.glLinkProgram(self.program)
# Get rid of shaders (not needed anymore)
GL.glDetachShader(self.program, self.vertex)
GL.glDetachShader(self.program, self.fragment)
# Make program the default program
GL.glUseProgram(self.program)
# Create array object
self.vao = GL.glGenVertexArrays(1)
GL.glBindVertexArray(self.vao)
# Request buffer slot from GPU
self.x_data_buffer = GL.glGenBuffers(1)
GL.glBindBuffer(GL.GL_ARRAY_BUFFER, self.x_data_buffer)
GL.glBufferData(GL.GL_ARRAY_BUFFER, ArrayDatatype.arrayByteCount(self.x), self.x, GL.GL_DYNAMIC_DRAW)
self.y_data_buffer = GL.glGenBuffers(1)
GL.glBindBuffer(GL.GL_ARRAY_BUFFER, self.y_data_buffer)
GL.glBufferData(GL.GL_ARRAY_BUFFER, ArrayDatatype.arrayByteCount(self.y), self.y, GL.GL_DYNAMIC_DRAW)
## Bind attributes
#self.stride = self.x.strides[0]
#self.offset = ctypes.c_void_p(0)
self.loc = GL.glGetAttribLocation(self.program, "x_position".encode('utf-8'))
GL.glEnableVertexAttribArray(self.loc)
GL.glBindBuffer(GL.GL_ARRAY_BUFFER, self.x_data_buffer)
GL.glVertexAttribPointer(self.loc, 1, GL.GL_FLOAT, GL.GL_FALSE, 0, 0)
#self.stride = self.y.strides[0]
#self.offset = ctypes.c_void_p(0)
self.loc = GL.glGetAttribLocation(self.program, "y_position".encode('utf-8'))
GL.glEnableVertexAttribArray(self.loc)
GL.glBindBuffer(GL.GL_ARRAY_BUFFER, self.y_data_buffer)
GL.glVertexAttribPointer(self.loc, 1, GL.GL_FLOAT, GL.GL_FALSE, 0, 0)
def resizeGL(self, width, height):
if height == 0: height = 1
GL.glViewport(0, 0, width, height)
GL.glMatrixMode(GL.GL_PROJECTION)
GL.glLoadIdentity()
aspect = width / float(height)
GLU.gluPerspective(45.0, aspect, 1.0, 100.0)
GL.glMatrixMode(GL.GL_MODELVIEW)
def paintGL(self):
GL.glClear(GL.GL_COLOR_BUFFER_BIT | GL.GL_DEPTH_BUFFER_BIT)
GL.glDrawArrays(GL.GL_LINE_STRIP, 0, self.bins)
def initGeometry(self):
self.bins = 1000
self.x = np.linspace(-0.5,0.5,self.bins)
self.y = np.array([np.sin(val*2*np.pi) for val in self.x])
self.color = np.array([(1,1,1,1) for x in np.arange(self.bins)])
def addPoint(self, point):
#print('ADD POINT')
self.y[self.current_position] = point
if self.current_position < self.bins-1:
self.current_position += 1
else:
self.current_position = 0
return True
def render(self):
#print('RENDER')
self.updateGL()
return True
I also put a full working version of the program here:
import sys
from PyQt5.QtWidgets import QDesktopWidget, QMainWindow, QWidget, QAction, qApp, QApplication, QHBoxLayout, QVBoxLayout, QPushButton
from PyQt5.QtCore import QTimer
from PyQt5.QtGui import QIcon
from PyQt5 import QtOpenGL
from OpenGL import GL
from OpenGL import GLU
from OpenGL.arrays.arraydatatype import ArrayDatatype
import ctypes
import numpy as np
from threading import Timer, Thread, Event
class OxySensor(QMainWindow):
def __init__(self):
super().__init__()
self.initUI()
self.initActions()
self.initMenuBar()
self.initRenderTimer()
self.start()
def initUI(self):
self.resize(800,600)
self.center()
self.setWindowTitle('OxySensor')
okButton = QPushButton("OK")
cancelButton = QPushButton("Cancel")
hbox = QHBoxLayout()
hbox.addStretch(1)
hbox.addWidget(okButton)
hbox.addWidget(cancelButton)
vbox = QVBoxLayout()
#vbox.addStretch(1)
self.gl_widget = GLWidget()
vbox.addWidget(self.gl_widget)
vbox.addLayout(hbox)
mainWidget = QWidget(self)
mainWidget.setLayout(vbox)
self.setCentralWidget(mainWidget)
self.show()
def initActions(self):
self.exitAction = QAction(QIcon('images/close20.png'), '&Exit', self)
self.exitAction.setShortcut('Ctrl+W')
self.exitAction.setStatusTip('Exit application')
self.exitAction.triggered.connect(self.onExit)
def initMenuBar(self):
menubar = self.menuBar()
fileMenu = menubar.addMenu('&File')
fileMenu.addAction(self.exitAction)
return True
def initRenderTimer(self):
self.timer = QTimer()
self.timer.timeout.connect(self.gl_widget.render)
self.timer.start(100)
return True
def start(self):
self.stop_flag = Event()
self.thread = SerialPort(self.onTimerExpired, self.stop_flag)
self.thread.start()
self.statusBar().showMessage('Ready')
def center(self):
qr = self.frameGeometry()
cp = QDesktopWidget().availableGeometry().center()
qr.moveCenter(cp)
self.move(qr.topLeft())
return True
def onTimerExpired(self):
data = np.random.uniform(-1,1)
self.gl_widget.addPoint(data)
return True
def onExit(self):
self.close()
return None
def closeEvent(self,event):
self.stop_flag.set()
event.accept()
return None
class GLWidget(QtOpenGL.QGLWidget):
def __init__(self, parent=None):
self.parent = parent
QtOpenGL.QGLWidget.__init__(self, parent)
self.yRotDeg = 0.0
self.current_position = 0
def initializeGL(self):
self.initGeometry()
self.vertex_code = """
#version 120
attribute vec4 color;
attribute float x_position;
attribute float y_position;
varying vec4 v_color;
void main()
{
gl_Position = vec4(x_position, y_position, 0.0, 1.0);
v_color = color;
} """
self.fragment_code = """
#version 120
varying vec4 v_color;
void main()
{
//gl_FragColor = v_color;
gl_FragColor = vec4(1,1,1,1);
} """
## Build and activate program
# Request program and shader slots from GPU
self.program = GL.glCreateProgram()
self.vertex = GL.glCreateShader(GL.GL_VERTEX_SHADER)
self.fragment = GL.glCreateShader(GL.GL_FRAGMENT_SHADER)
# Set shaders source
GL.glShaderSource(self.vertex, self.vertex_code)
GL.glShaderSource(self.fragment, self.fragment_code)
# Compile shaders
GL.glCompileShader(self.vertex)
GL.glCompileShader(self.fragment)
# Attach shader objects to the program
GL.glAttachShader(self.program, self.vertex)
GL.glAttachShader(self.program, self.fragment)
# Build program
GL.glLinkProgram(self.program)
# Get rid of shaders (not needed anymore)
GL.glDetachShader(self.program, self.vertex)
GL.glDetachShader(self.program, self.fragment)
# Make program the default program
GL.glUseProgram(self.program)
# Create array object
self.vao = GL.glGenVertexArrays(1)
GL.glBindVertexArray(self.vao)
# Request buffer slot from GPU
self.x_data_buffer = GL.glGenBuffers(1)
GL.glBindBuffer(GL.GL_ARRAY_BUFFER, self.x_data_buffer)
GL.glBufferData(GL.GL_ARRAY_BUFFER, ArrayDatatype.arrayByteCount(self.x), self.x, GL.GL_DYNAMIC_DRAW)
self.y_data_buffer = GL.glGenBuffers(1)
GL.glBindBuffer(GL.GL_ARRAY_BUFFER, self.y_data_buffer)
GL.glBufferData(GL.GL_ARRAY_BUFFER, ArrayDatatype.arrayByteCount(self.y), self.y, GL.GL_DYNAMIC_DRAW)
## Bind attributes
#self.stride = self.x.strides[0]
#self.offset = ctypes.c_void_p(0)
self.loc = GL.glGetAttribLocation(self.program, "x_position".encode('utf-8'))
GL.glEnableVertexAttribArray(self.loc)
GL.glBindBuffer(GL.GL_ARRAY_BUFFER, self.x_data_buffer)
GL.glVertexAttribPointer(self.loc, 1, GL.GL_FLOAT, GL.GL_FALSE, 0, 0)
#self.stride = self.y.strides[0]
#self.offset = ctypes.c_void_p(0)
self.loc = GL.glGetAttribLocation(self.program, "y_position".encode('utf-8'))
GL.glEnableVertexAttribArray(self.loc)
GL.glBindBuffer(GL.GL_ARRAY_BUFFER, self.y_data_buffer)
GL.glVertexAttribPointer(self.loc, 1, GL.GL_FLOAT, GL.GL_FALSE, 0, 0)
def resizeGL(self, width, height):
if height == 0: height = 1
GL.glViewport(0, 0, width, height)
GL.glMatrixMode(GL.GL_PROJECTION)
GL.glLoadIdentity()
aspect = width / float(height)
GLU.gluPerspective(45.0, aspect, 1.0, 100.0)
GL.glMatrixMode(GL.GL_MODELVIEW)
def paintGL(self):
GL.glClear(GL.GL_COLOR_BUFFER_BIT | GL.GL_DEPTH_BUFFER_BIT)
GL.glDrawArrays(GL.GL_LINE_STRIP, 0, self.bins)
def initGeometry(self):
self.bins = 1000
self.x = np.linspace(-0.5,0.5,self.bins)
self.y = np.array([np.sin(val*2*np.pi) for val in self.x])
self.color = np.array([(1,1,1,1) for x in np.arange(self.bins)])
def addPoint(self, point):
#print('ADD POINT')
self.y[self.current_position] = point
if self.current_position < self.bins-1:
self.current_position += 1
else:
self.current_position = 0
return True
def render(self):
#print('RENDER')
self.updateGL()
return True
class SerialPort(Thread):
def __init__(self, callback, event):
Thread.__init__(self)
self.callback = callback
self.stopped = event
return None
def SetInterval(self, time_in_seconds):
self.delay_period = time_in_seconds
return True
def run(self):
while not self.stopped.wait(0.1):
self.callback()
return True
if __name__ == '__main__':
app = QApplication(sys.argv)
oxy_sensor = OxySensor()
sys.exit(app.exec_())
970
The problem is most likely that call of the 'OpenGL.GL' function:
GL.glVertexAttribPointer(self.loc, 1, GL.GL_FLOAT, GL.GL_FALSE, 0, 0)
Note the last value is 0 (which unfortunately doesn't translate to (void *)0 in the C++ API, but instead to some high address). You most likely mean "offset 0" as opposed to "the address of the 0 object". I. e. use None instead (which does translate to (void *)0):
GL.glVertexAttribPointer(self.loc, 1, GL.GL_FLOAT, GL.GL_FALSE, 0, None)
Yes, it's kinda counterintuitive. It took me half a day to figure out that's what made the output black in my own code.
Also note that if instead of the OpenGL.GL functions you use the Qt ones (that you get via gl = self.context().versionFunctions()), they provide a slightly different API and there you actually pass 0 when you mean "Offset 0".
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