Can't enable depth test with OpenGL in QWIndow (Qt5) - c++

Question

I'm trying to write a simple OpenGL application in Qt 5.2 using a QWindow. I can't seem to enable depth testing. I've simplified the QWindow OpenGL example heavily: I'm drawing a triangle with coloured vertices, followed by a triangle with white vertices. The white triangle has larger Z coordinates, so should appear behind the coloured triangle. It doesn't.
I'm explicitly setting the QWindow's surface format's depth buffer size to 24, but when I check with the QWindow::format() function, the depth buffer size is 0. With QGLFormat, I know there's a setDepth() function that you can use to turn on the depth buffer, but there's no similar function in QSurfaceFormat.
What am I doing wrong?
My code...
testWindow.cpp:
#include <QApplication>
#include <QDialog>
#include <QLabel>
#include <QResizeEvent>
#include <QSurfaceFormat>
#include <QWidget>
#include <QWindow>
#include <QVBoxLayout>
#include "SphereWindow.h"
class GLDialog : public QDialog
{
public:
GLDialog(QWidget *parent = 0, Qt::WindowFlags f = 0) : QDialog(parent, f)
{
QVBoxLayout *layout = new QVBoxLayout(this);
QSurfaceFormat format;
format.setSamples(16);
format.setDepthBufferSize(24);
qDebug() << "requested format:" << format;
window = new SphereWindow;
window->setFormat(format);
qDebug() << "actual format:" << window->format();
window->render();
QWidget *glWidget = QWidget::createWindowContainer(window, this);
layout->addWidget(glWidget);
}
~GLDialog()
{
delete window;
}
protected:
void resizeEvent(QResizeEvent *event)
{
window->resize(event->size());
window->render();
}
private:
SphereWindow *window;
};
int main(int argc, char **argv)
{
QApplication app(argc, argv);
QDialog *dlg = new GLDialog;
dlg->resize(640,480);
dlg->show();
return app.exec();
}
SphereWindow.h:
#include <QColor>
#include <QEvent>
#include <QExposeEvent>
#include <QOpenGLContext>
#include <QOpenGLFunctions>
#include <QOpenGLPaintDevice>
#include <QOpenGLShaderProgram>
#include <QPainter>
#include <QResizeEvent>
#include <QSize>
#include <QWindow>
class SphereWindow : public QWindow, protected QOpenGLFunctions
{
Q_OBJECT
public:
SphereWindow(QWindow * = 0);
virtual ~SphereWindow();
virtual void render();
virtual void initialize();
public slots:
void resizeViewport(const QSize &);
protected:
virtual void resizeEvent(QResizeEvent *);
private:
bool _initialized;
QOpenGLContext *_context;
QOpenGLPaintDevice *_device;
QOpenGLShaderProgram *_program;
QColor _backgroundColour;
GLuint _posAttr;
GLuint _colAttr;
};
SphereWindow.cpp:
#include <QCoreApplication>
#include <QMatrix4x4>
#include <QOpenGLShader>
#include <QScreen>
#include <QSurfaceFormat>
#include <QDebug>
#include "SphereWindow.h"
SphereWindow::SphereWindow(QWindow *parent)
: QWindow(parent),
_initialized(0),
_program(0),
_backgroundColour(Qt::black)
{
setSurfaceType(QWindow::OpenGLSurface);
create();
_context = new QOpenGLContext(this);
_context->setFormat(requestedFormat());
_context->create();
}
SphereWindow::~SphereWindow()
{ }
void SphereWindow::resizeEvent(QResizeEvent *event)
{
resizeViewport(event->size());
}
void SphereWindow::resizeViewport(const QSize &size)
{
int width = size.width();
int height = size.height();
int side = qMin(width, height);
int hoffset = (int)((width - side) / 2.0 + 0.5);
int voffset = (int)((height - side) / 2.0 + 0.5);
glViewport(hoffset, voffset, side, side);
}
void SphereWindow::render()
{
if (! _initialized)
initialize();
if (! isExposed()) return;
glEnable(GL_DEPTH_TEST);
_context->makeCurrent(this);
glClearColor(_backgroundColour.redF(), _backgroundColour.greenF(), _backgroundColour.blueF(), 1.0);
glClear(GL_COLOR_BUFFER_BIT|GL_DEPTH_BUFFER_BIT);
_program->bind();
GLfloat vertices[] = {
-0.75f, 0.75f, 0.0f,
-0.75f, -0.75f, 0.0f,
0.75f, -0.75f, 0.0f,
0.75f, 0.75f, 0.5f,
0.75f, -0.75f, 0.5f,
-0.75f, -0.75f, 0.5f,
};
GLfloat colors[] = {
1.0f, 0.0f, 0.0f,
0.0f, 1.0f, 0.0f,
0.0f, 0.0f, 1.0f,
1.0f, 1.0f, 1.0f,
1.0f, 1.0f, 1.0f,
1.0f, 1.0f, 1.0f,
};
glVertexAttribPointer(_posAttr, 3, GL_FLOAT, GL_FALSE, 0, vertices);
glVertexAttribPointer(_colAttr, 3, GL_FLOAT, GL_FALSE, 0, colors);
glEnableVertexAttribArray(0);
glEnableVertexAttribArray(1);
glDrawArrays(GL_TRIANGLES, 0, 6);
glDisableVertexAttribArray(1);
glDisableVertexAttribArray(0);
_program->release();
_context->swapBuffers(this);
_context->doneCurrent();
}
static const char *vertexShaderSource =
"attribute highp vec4 posAttr;\n"
"attribute lowp vec4 colAttr;\n"
"varying lowp vec4 col;\n"
"void main() {\n"
" col = colAttr;\n"
" gl_Position = posAttr;\n"
"}\n";
static const char *fragmentShaderSource =
"varying lowp vec4 col;\n"
"void main() {\n"
" gl_FragColor = col;\n"
"}\n";
void SphereWindow::initialize()
{
_context->makeCurrent(this);
_program = new QOpenGLShaderProgram(this);
_program->addShaderFromSourceCode(QOpenGLShader::Vertex, vertexShaderSource);
_program->addShaderFromSourceCode(QOpenGLShader::Fragment, fragmentShaderSource);
_program->link();
_program->bind();
_posAttr = _program->attributeLocation("posAttr");
_colAttr = _program->attributeLocation("colAttr");
_program->release();
initializeOpenGLFunctions();
}
testqwindow.pro:
######################################################################
# Automatically generated by qmake (3.0) Sat May 3 05:01:55 2014
######################################################################
TEMPLATE = app
TARGET = testqwindow
INCLUDEPATH += .
QT += widgets
CONFIG += debug
# Input
HEADERS += SphereWindow.h
SOURCES += SphereWindow.cpp testWindow.cpp

Answer 1

The problem was this: I was setting the surface format after calling my SphereWindow constructor, but creating a QOpenGLContext and setting its format inside the constructor. The result was that the context wasn't getting a depth buffer. I've moved the calls to QOpenGLContext::setFormat() and QOpenGLContext::create() to my SphereWindow::initialize() function, and depth buffering is working for me now.
SphereWindow::SphereWindow(QWindow *parent)
: QWindow(parent),
_initialized(0),
_program(0),
_backgroundColour(Qt::black)
{
setSurfaceType(QWindow::OpenGLSurface);
create();
qDebug() << "format:" << format();
_context = new QOpenGLContext(this);
/* Move these lines into initialize() */
// _context->setFormat(requestedFormat());
// _context->create();
}
...
void SphereWindow::initialize()
{
_context->setFormat(requestedFormat());
_context->create();
_context->makeCurrent(this);
_program = new QOpenGLShaderProgram(this);
_program->addShaderFromSourceCode(QOpenGLShader::Vertex, vertexShaderSource);
_program->addShaderFromSourceCode(QOpenGLShader::Fragment, fragmentShaderSource);
_program->link();
_program->bind();
_posAttr = _program->attributeLocation("posAttr");
_colAttr = _program->attributeLocation("colAttr");
_program->release();
initializeOpenGLFunctions();
}
As I mentioned in a comment above, I had pretty much identical code in a QGLWidget-based setup, and depth buffering worked "out of the box". I guess QGLWidget (or QGLFormat?) must have a depth buffer turned on by default, and QWindow (or QSurfaceFormat?) doesn't.