I'm new to OpenGL and Glut. There is a project implemented by Glut. I googled and found that there is an OpenGL implementation in Qt, called QGLWidget. However, it's hard for me converting the old Glut code to new Qt code since I don't know how to find equivalent function for Glut functions in Qt. Part of the code look like this:
glutInit(&argc,argv);
glutInitDisplayMode(GLUT_DOUBLE|GLUT_RGB);
glutInitWindowSize(gray1->width,gray1->height);
glutInitWindowPosition(100,100);
glutCreateWindow("hello");
init();
glutDisplayFunc(&display);
glutReshapeFunc(reshape);
glutMouseFunc(mouse);
glutMotionFunc(mouse_move);
glutMainLoop();
The glut* functions above don't exist in Qt's document. So my problem is how can I find equivalent glut functions in functions of QGLWidget?
You need to implement your own class inherited from QGLWidget, for example:
class GLWidget : public QGLWidget
{
Q_OBJECT
public:
GLWidget(QWidget *parent = 0);
protected:
void initializeGL();
void resizeGL(int w, int h);
void paintGL();
void mousePressEvent(QMouseEvent *event);
void mouseMoveEvent(QMouseEvent *event);
void mouseReleaseEvent(QMouseEvent *event);
};
You also need to override three important functions, initializeGL() where you're preparing your OpenGL. resizeGL() where you update the viewport and projection matrix if your panel is resized, and paintGL() the actual rendering.
The window initialization, of course, is handled by Qt.
For mouse events, there are three functions you can override: mousePressEvent(), mouseMoveEvent(), and mouseReleaseEvent()
void GLWidget::initializeGL()
{
glClearColor(0.5, 0.5, 0.5, 1.0);
}
void GLWidget::resizeGL(int width, int height)
{
glViewport(0, 0, width(), height());
glMatrixMode(GL_PROJECTION);
glLoadIdentity();
gluOrtho2D(0, width(), 0, height());
glMatrixMode(GL_MODELVIEW);
glLoadIdentity();
}
void GLWidget::paintGL()
{
glClear(GL_COLOR_BUFFER_BIT);
// draw a red triangle
glColor3f(1,0,0);
glBegin(GL_POLYGON);
glVertex2f(10,10);
glVertex2f(10,600);
glVertex2f(300,10);
glEnd();
}
OK. Have you looked at the HelloGL sample?
So there you'll learn how to display a QGLWidget and process mouse input. I think this is what you are looking for.
Since Qt provides SIGNAL and SLOTS input processing is kind of different but also very intuitive. So you have to connect mouse SIGNALS to your SLOTS. Those SLOTS will then process the mouse event.
But look at the sample, it's quite intuitive.
Related
I am working on my project from programming and I need to draw, for example, a circle every time the pushButton is pressed using QPainter. This is the first problem, and the second one here is that I need some information to be sent to the drawing function too, for example, int vector, and being able to draw so many circles, as there are elements in the vector with radii of the elements itself. I have found some code based on signals and slots.
The sender:
public:
Listener(QObject *p = 0) : QObject(p) {
QTimer * t = new QTimer(this);
t->setInterval(200);
connect(t, SIGNAL(timeout()), this, SLOT(sendData()));
t->start();
}
signals:
void dataAvaiable(int, int);
public slots:
void sendData() {
emit dataAvaiable(qrand() % 200, qrand() % 200);
}
The reciever:
void receiveData(int x, int y) {
QPainter painter(this);
QPen pen(Qt::white, 5);
painter.setRenderHint(QPainter::HighQualityAntialiasing);
painter.setPen(pen);
QPoint point(x, y);
painter.drawEllipse(x, y, 100, 100);
data.append(point);
}
The connection itself in main.cpp
QObject::connect(&l, SIGNAL(dataAvaiable(int,int)), &w, SLOT(receiveData(int,int)));
But the code doesn't suit for my exact task with buttons and doesn't even want to draw anythig, just any circle at all. Howewer, in debugger the code executes properly, and I am relatively new to Qt and C++ so I can't figure out by myself, where the problem is and how to solve my task.Can someone please do a minimal of code or simply explain to me, where exactly the problem is? Need to solve the problem as soon as possible. Thank you.
Upd: any possible solution with or without QPainter would be good now.
Qt Forum users gave me an answer.
Quote:
From the QPainter class description:
Warning: When the paintdevice is a widget, QPainter can only be used inside a
paintEvent() function or in a function called by paintEvent().
You can force calling paintEvent() by invoking update(), so you must connect the onclicked() signal of your button to the update() slot of the widget you're drawing on.
For your second problem, the data can be a member variable.
Here's an example:
// mywidget.h
#include <QVector>
#include <QPoint>
// other includes and the constructor...
protected:
virtual void paintEvent(QPaintEvent *event);
private slots:
void onButtonClicked();
private:
QPushButton* mButton;
QVector<QPoint> mCirclesData;
// mywidget.cpp
MyWidget::MyWidget(QWidget *parent) : QWidget(parent)
{
mButton = new QPushButton(this);
// customise your button...
connect(mButton, &QPushButton::clicked, this, &MyWidget::onButtonClicked);
}
//...
void MyWidget::onButtonClicked(){
int x = qrand() % 200, y = x;
mCirclesData << QPoint(x,y);
update(); // force calling paintEvent
}
void MyWidget::paintEvent(QPaintEvent *event)
{
QPainter painter(this);
QPen pen(Qt::white, 5);
painter.setRenderHint(QPainter::HighQualityAntialiasing);
painter.setPen(pen);
painter.drawEllipse(mCirclesData.last().x(), mCirclesData.last().y(), 100, 100);
}
``
I have the following class inheriting from QOpenGLWidget and QOpenGLFunctions:
class OpenGLWidget : public QOpenGLWidget, protected QOpenGLFunctions
{
Q_OBJECT
public:
OpenGLWidget();
virtual ~OpenGLWidget();
void initializeGL();
void paintGL()
{
QPainter painter(this);
painter.beginNativePainting();
glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
// Calls OpenGL draw functions with VBOs
m_viewport.render(m_shader, m_entities);
painter.endNativePainting();
painter.drawText(0, 0, width(), height(), Qt::AlignCenter, "Hello World!");
}
void resizeGL(int width, int height);
[...]
}
"Hello World" is drawn as intended, but the 3D scene is broken. I should have 3D axis in the center and in the top-right of the screen:
To me, it seems that the vertex and fragment shaders I'm using are the source of the problem. Otherwise, given the simplicity of the code and the examples I've found, it should work.
A good output would be:
with the "Hello World" at the center. This is what I get when I comment the QPainter calls.
It seems that your shader program is released when you use QPainter. Bind the shader program before OpenGL calls and release it afterwards. It should fix it.
painter.beginNativePainting();
// Bind shader program
glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
// Calls OpenGL draw functions with VBOs
m_viewport.render(m_shader, m_entities);
// Release shader program
painter.endNativePainting();
I am pretty new to Qt so sorry if this is a straight forward question.
I am using Qt 5.5 and trying to visualize a point cloud in QOpenGLWidget.
This is my header:
class PointCloudWindow : public QOpenGLWidget
{
public:
void setDepthMap(DepthMapGrabber* grabber);
protected:
void initializeGL();
void paintGL();
private:
QMatrix4x4 m_projection;
DepthMapGrabber* m_grabber;
};
and here is the corresponding cpp:
void PointCloudWindow::setDepthMap(DepthMapGrabber* grabber) {
m_grabber = grabber;
QTimer* updatePointCloud = new QTimer(this);
connect(updatePointCloud, SIGNAL(timeout()), SLOT(update()));
updatePointCloud->start();
}
void PointCloudWindow::initializeGL() {
glewInit(); // TODO: check for return value if error occured
glEnable(GL_DEPTH_TEST);
glClearColor(0.0f, 0.0f, 0.0f, 1.0f);
glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
}
void PointCloudWindow::paintGL() {
m_grabber->getNextDepthFrame(); // TODO: check for return value if error occured
m_projection.setToIdentity();
m_projection.perspective(45.0f, width() / (float)height(), 0.01f, 100.0f);
if (m_grabber->getDepthMap()->cloud) {
glBegin(GL_POINTS);
glColor3f(0.8f, 0.8f, 0.8f);
for (UINT i = 0; i < m_grabber->getDepthMap()->size; ++i)
{
glVertex3f(m_grabber->getDepthMap()->cloud[i].X, m_grabber->getDepthMap()->cloud[i].Y, m_grabber->getDepthMap()->cloud[i].Z);
}
glEnd();
}
}
This is how my point cloud looks like after visualization:
My problem is that as you can see (monitor is cut in half for example) if a point has a z value, which is bigger, then 1.0 then it gets clipped of. I tried to set the near and far plane, but no effect. I searched through Google and tried several things, but was unable to figure out how this works in Qt. I manged to visualize this point cloud with OpenGL and GLUT before. Any help or explanation how to do this in Qt would be much appreciated!
m_projection is just a member variable in your class. It's not going to automatically "jump" into the OpenGL context. You've to explicitly load it into OpenGL. Normally you'd load a matrix like that into a uniform for use in a shader. But since you're not using shaders (booo! ;-) ) and use old, ugly and slow immediate mode (don't do that) you'll have to load it into the fixed function projection matrix.
glMatrixMode(GL_PROJECTION);
glLoadMatrixd(m_projection.constData());
I have small problem with QOpenGLWidget and its background color.
When I want to create semi-transparent rect on my custom QOpenGLWidget using QPainter there are 2 different results:
If MyCustomWidget have parent - on every update rect's color multiplies (and after few repaints it is opaque, like previous painting result not cleaned)
If MyCustomWidget doesn't have parent - color doesn't repaints each time
Here is code example for QPainter:
class Widget : public QOpenGLWidget
{
Q_OBJECT
public:
Widget(QWidget *parent = 0)
: QOpenGLWidget(parent)
{
resize(800, 600);
Test *test = new Test(this);
}
~Widget(){}
protected:
void paintEvent(QPaintEvent *) {}
protected:
void initializeGL() {
if(paintEngine()->type() != QPaintEngine::OpenGL &&
paintEngine()->type() != QPaintEngine::OpenGL2)
qDebug() << "ERROR. Type is: " << paintEngine()->type();
}
void resizeGL(int, int) {}
void paintGL() {
QPainter p;
p.begin(this);
{
p.fillRect(rect(), Qt::white);
}
p.end();
}
private:
class Test : public QOpenGLWidget
{
public:
Test(QWidget *parent = 0) : QOpenGLWidget(parent) {
resize(100, 100);
}
protected:
void paintEvent(QPaintEvent *) {
QPainter p(this);
p.fillRect(rect(), QColor(125, 125, 125, 255/10));
}
};
};
Also by default it has black background (I don't know how to fix it. setAttribute(Qt::WA_TranslucentBackground) doesn't helps).
Also, when I'm trying to clear color using glClear it ignores alpha (both on QOpenGLWidget with parent and not). Here is Test class from previous code, but now it is using opengl to clear color:
class Test : public QOpenGLWidget
{
public:
Test(QWidget *parent = 0) : QOpenGLWidget(parent) {
resize(100, 100);
}
void initializeGL() {
QOpenGLFunctions *f = context()->functions();
f->glClearColor(0.0f, 1.0f, 0.0f, 0.1f);
}
void paintGL() {
QOpenGLFunctions *f = context()->functions();
f->glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
}
};
How can I fix this problems?
I'm using Qt 5.5.0, Windows 10, MinGW 4.9.2
Xeed is correct when saying the QOpenGLWidget is painted first.
I'm not an expert but I think I found the solution. You need to set a widget attribute to always make the widget stacked on top (think of the widgets as layers on the window). Here is a link to where I got the following information:
P.S. As mentioned in the QQuickWidget post, there is a limitation regarding semi-transparency when using QQuickWidget or QOpenGLWidget as child widgets. For applications that absolutely need this, Qt 5.4 offers a workaround: the newly introduced Qt::WA_AlwaysStackOnTop widget attribute. This, at the expense of breaking the stacking order for other types of layouts, makes it possible to have a semi-transparent QQuickWidget or QOpenGLWidget with other widgets visible underneath. Of course, if the intention is only to make other applications on the desktop visible underneath, then the Qt::WA_TranslucentBackground attribute is sufficient
Solution in Python:
set attribute of OpenGL widget
setAttribute(Qt.WA_AlwaysStackOnTop)
Now the OpenGL widget is considered 'on top' in the window. Use 'glClearColor' function and specify the alpha channel to be zero (0.0).
glClearColor(0.0, 0.0, 0.0, 0.0)
I'm not sure how to write that in other languages but this worked for me. The OpenGL widget no longer has the default black background. It is transparent! Hope this helps.
As far as I know the QOpenGLWidget is always drawn first. Therefore you cannot show any widgets layered below. I'm currently looking into the same issue. I'll report back, when I find any solution.
I've had similar issue with QOpenGLWidget not repainting correctly in transparent areas and decided to switch to QOpenGLWindow wrapped inside QWidget::createWindowContainer()
I'm starting off QT 4.6's example "OpenGL - 2D painting"
It uses a subclass of QGLWidget, and makes painting operations with the class QPainter.
I'd like to know how to do drawing directly with OpenGL functions on the OpenGL Widget.
If you use the widget as described in its manual, you can just use the OpenGL functions as usual. For example (copied from the manual):
class MyGLDrawer : public QGLWidget
{
Q_OBJECT // must include this if you use Qt signals/slots
public:
MyGLDrawer(QWidget *parent)
: QGLWidget(parent) {}
protected:
void initializeGL()
{
// Set up the rendering context, define display lists etc.:
...
glClearColor(0.0, 0.0, 0.0, 0.0);
glEnable(GL_DEPTH_TEST);
...
}
void resizeGL(int w, int h)
{
// setup viewport, projection etc.:
glViewport(0, 0, (GLint)w, (GLint)h);
...
glFrustum(...);
...
}
void paintGL()
{
// draw the scene:
...
glRotatef(...);
glMaterialfv(...);
glBegin(GL_QUADS);
glVertex3f(...);
glVertex3f(...);
...
glEnd();
...
}
};