What steps are necessary to enable antialiasing when using a QPainter on a QGLWidget?

Question

I am trying to draw basic shapes on a QGLWidget. I am trying to enable antialiasing to smooth out the lines, but it is not working.

This is what I am trying at the m

Answer 1

This question is quite old but I still found it on Google. You shouldn't use QGLWidget any more. Use the newer QOpenGLWidget. This renders the scene off-screen rather than creating a native OpenGL window which causes all sorts of issues with resizing layouts. This code works for me. Put it in your QGraphicsView constructor:

QOpenGLWidget* gl = new QOpenGLWidget;
QSurfaceFormat fmt;
fmt.setSamples(8);
gl->setFormat(fmt);
setViewport(gl);
setRenderHint(QPainter::Antialiasing);

Answer 2

I found the solution. When debugging a different issue, I found messages in my debug output to the effect that you can't set renderhints before the call to begin().

The following works:

QGLWidget *widget = ui->renderWidget;

QPainter painter;

widget->makeCurrent();
glEnable(GL_MULTISAMPLE);
glEnable(GL_LINE_SMOOTH);

painter.begin(widget);

painter.setRenderHint(QPainter::Antialiasing);
painter.setRenderHint(QPainter::HighQualityAntialiasing);

Answer 3

If you work on PyQt5, you will typically subclass QOpenGLWidget() to build your own GPU-powered widget. To turn on anti-aliasing, have a look at the code snippet below:

from PyQt5.QtWidgets import *
from PyQt5.QtGui import *
from PyQt5.QtCore import *

class MyFigureClass(QOpenGLWidget):
    def __init__(self, parent):
        super().__init__(parent)
        fmt = QSurfaceFormat()    # -╷
        fmt.setSamples(8)         #  > anti-aliasing
        self.setFormat(fmt)       # -╵
        [...]

    def paintEvent(self, event):
        qp = QPainter()
        qp.begin(self)
        qp.setRenderHint(QPainter.Antialiasing)
        [...]
        qp.end()

_{Note: Thank you @Timmmm for your answer. I found the PyQt5 solution when looking at your C++ code snippets.}

Answer 4

You can try to enable the antialiasing on the complete Widget :

QGLWidget::setFormat(QGLFormat(QGL::SampleBuffers));