Qt-interest Archive, January 2007
[Qt 4.2.1] QPainter, QWidget, QGLWidget and transparency
Message 1 in thread
Hi All!
I've met a trouble with translucent widgets in Qt4. I have the following code:
TestChildWidget.hpp
#ifndef __TEST_CHILD_WIDGET_HPP
#define __TEST_CHILD_WIDGET_HPP
#include <QWidget>
class TestChildWidget : public QWidget
{
Q_OBJECT
public:
TestChildWidget(QWidget * parent = NULL);
~TestChildWidget() {};
};
#endif
TestChildWidget.cpp
#include <TestChildWidget.hpp>
#include <QPalette>
TestChildWidget::TestChildWidget(QWidget * parent/* = NULL*/)
: QWidget(parent)
{
QPalette pal(palette());
pal.setColor(QPalette::Window, QColor(255, 0, 0, 120));
setPalette(pal);
setAutoFillBackground(true);
};
TestWidget.hpp
#ifndef __TEST_WIDGET_HPP
#define __TEST_WIDGET_HPP
#include <QWidget>
class QPaintEvent;
class TestWidget : public QWidget
{
Q_OBJECT
public:
TestWidget(QWidget * parent = NULL);
~TestWidget() {};
protected:
void paintEvent(QPaintEvent * event);
};
#endif
TestWidget.cpp
#include <TestWidget.hpp>
#include <QPainter>
#include <QPaintEvent>
#include <QPalette>
TestWidget::TestWidget(QWidget * parent/* = NULL*/)
: QWidget(parent)
{
QPalette pal(palette());
pal.setColor(QPalette::Window, QColor(255, 255, 255, 255));
setPalette(pal);
setAutoFillBackground(true);
};
void TestWidget::paintEvent(QPaintEvent * event)
{
QPainter painter;
painter.begin(this);
painter.setRenderHint(QPainter::TextAntialiasing);
painter.drawText(30, 30, "TEST STRING!!!!");
painter.end();
};
main.cpp
#include <TestWidget.hpp>
#include <TestChildWidget.hpp>
#include <QApplication>
int main(int argc, char ** argv)
{
QApplication app(argc, argv);
TestWidget * parent = new TestWidget();
TestChildWidget * child = new TestChildWidget(parent);
TestChildWidget * child2 = new TestChildWidget(parent);
parent->resize(200, 100);
child->resize(50, 50);
child2->resize(50, 50);
child->move(10, 10);
child2->move(20, 20);
parent->show();
return app.exec();
};
This code works well: it creates the window, outputs the test string to it and
paints to translucent widgets over it. Everything looks nice. But when I
tried to change base class of TestWidget and TestChildWidget from QWidget to
QGLWidget (so i try to use OpenGL to speed up the rendering) i receive bad
result. There is a window, but instead of translucent widgets i get two black
rectangles.
Does anybody have any ideas to solve this issue?...
WBR, Gleb.
PS. Sorry for not-so-well English...
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Message 2 in thread
Hi,
Sectoid wrote:
> Hi All!
>
> I've met a trouble with translucent widgets in Qt4. I have the following code:
> TestChildWidget.hpp
[snip]
> This code works well: it creates the window, outputs the test string to it and
> paints to translucent widgets over it. Everything looks nice. But when I
> tried to change base class of TestWidget and TestChildWidget from QWidget to
> QGLWidget (so i try to use OpenGL to speed up the rendering) i receive bad
> result. There is a window, but instead of translucent widgets i get two black
> rectangles.
>
> Does anybody have any ideas to solve this issue?...
>
> WBR, Gleb.
>
> PS. Sorry for not-so-well English...
QGLWidgets are always considered to be opaque internally in Qt, and
can't have a semi-transparent background because of several reasons. In
short, the QGLWidgets do not participate in the compositing process that
takes place inside the internal Qt backingstore, which we use for
blending semi-transparent child widgets.
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