I'm having some trouble with the following code. I'm attempting to set a Mat as a QLabel pixmap. When I call QLabel::setPixmap(), nothing happens! The label in the dialog box stays exactly the same, showing placeholder text. It has been properly promoted to MyLabel.
//include stuff above
MyLabel::MyLabel(QWidget *parent): QLabel(parent)
{
boats = cv::imread("C:/boats.jpg");
setPixmap(boats);
}
void MyLabel::setPixmap(cv::Mat image){
cv::Mat converted;
cv::cvtColor(image, converted, CV_BGR2RGB);
QImage result = QImage((const unsigned char*)(converted.data),
converted.cols, converted.rows, QImage::Format_RGB888);
QLabel::setPixmap(QPixmap::fromImage(result));
}
I have also tried setting the pixmap in the following way:
QLabel::setPixmap(QPixmap("C:/boats.jpg"));
But this produces the same effect. Any ideas?
You should set image to the interface. For instance, you can set like this way:
ui->label_15->setPixmap(QPixmap::fromImage(result));
Related
I want to set a background image to my QTableView.
Inside the function i create a test QWidget and apply the image and it works perfectly.
The fp_widget i pass in is QTableView and here comes the problem.
The image is not shown / applied to the QTableView.
void setBackgroundImage(QWidget *fp_widget, const QPixmap &image)
{
QPalette palette;
palette.setBrush(QPalette::Background, image);
fp_widget->setPalette(palette);
QWidget *test = new QWidget;
test->setPalette(palette);
test->resize(800,800);
test->show();
}
I need to change the alpha of a QImage I have so it blends with the other QImages behind and infront of it. This needs to be toggled quickly on and off.
Previously I've had to recreate every single image and give them new colors with just a different alpha value. But now I want to retain that same original image instead of redrawing and painting it.
I'm trying to do it like this now:
QImage image;
unsigned int rgb;
for(int y=0;y<image.height();y++){
for(int x=0;x<image.width();x++){
rgb=image.pixel(x,y);
image.setPixel(x,y,qRgba(qRed(rgb),qGreen(rgb),qRed(rgb),120));
}
}
I'm getting some fairly unpredictable behavior. When I toggle the image sometimes I lose colors or the alpha isn't changed. And if the alpha did get changed when I toggle back (I hardcode the alpha 255 elsewhere instead of 120) it doesn't go back to normal.
This doesn't seem like the right way to do this anyways, it shouldn't be this difficult. It seems like there should be a single function call on an image to change the alpha but I haven't found one yet.
If you are using the QImage in QGraphicsView or in some other QWidget, you should look into this QGraphicsEffect:
http://qt-project.org/doc/qt-4.8/qgraphicsopacityeffect.html
http://doc-snapshot.qt-project.org/4.8/qwidget.html#setGraphicsEffect
http://doc-snapshot.qt-project.org/4.8/qgraphicsitem.html#setGraphicsEffect
If you are using a QLabel, I would try this out:
#include <QLabel>
#include <QPainter>
class TransparentQLabel : public QLabel
{
Q_OBJECT
public:
explicit TransparentQLabel() : QLabel() {}
~TransparentQLabel(){}
void setOpacity(const qreal & val)
{
if (this->pixmap() == null || this->pixmap().isNull())
return;
QPixmap result(this->pixmap()->size());
result.fill(Qt::transparent);
QPainter painter;
painter.begin(&result);
painter.setOpacity(val);
painter.drawPixmap(0, 0, *(this->pixmap()));
painter.end();
QLabel::setPixmap(result);
}
};
This next bit is only slightly related to your question, but it is nice to know. If you are layering outside of your QApplication onto the operating system, you need some things like this:
this->setWindowFlags( Qt::WindowStaysOnTopHint |
Qt::FramelessWindowHint | Qt::Tool);
this->setAttribute(Qt::WA_TranslucentBackground, true);
this->setAttribute (Qt::WA_TransparentForMouseEvents, true);
Here is an example of this stuff in action:
http://qt-project.org/wiki/QSplashScreen-Replacement-for-Semitransparent-Images
Hope that helps.
I'm using a QTextBrowser to display rich text including a number of images, each of them specified with a HTML <img> tag and added as resources using QTextDocument::addResource().
What I'd like to be able to do is, in a context menu handler (i.e. with a mouse click position available), identify the image that the click was over. It's possible to tell whether the click is over an image, because cursorForPosition(event->pos()).block().text() returns a string starting with Unicode 0xFFFC. Unfortunately the same string is returned for every image in the view.
It's possible to get all of the formats in use with QTextDocument::allFormats(), identify which of those are image formats, and get their image resource name. Unfortunately there seems to be no way to get their actual display position or bounding rectangle.
From the documentation:
Inline images are represented by an object replacement character (0xFFFC in Unicode) which has an associated QTextImageFormat. The image format specifies a name with setName() that is used to locate the image.
You can use charFormat().toImageFormat().name() on the cursor to extract the image's URL. Below is a self-contained example. There are two noteworthy details:
The cursor will sometimes point one character prior to the image. Thus the workaround; it seems necessary for both Qt 4.8.5 and 5.1.1.
The pop-up menus should be shown asynchronously so as not to block the rest of the application. The example code provided in the documentation is a source of bad user experience and should be considered an evil abomination. All widgets can automatically delete themselves when they get closed, so the menus won't leak. A QPointer is used only to demonstrate this fact. It tracks the menu's lifetime and nulls itself when the menu deletes itself.
#include <QApplication>
#include <QTextBrowser>
#include <QImage>
#include <QPainter>
#include <QMenu>
#include <QContextMenuEvent>
#include <QTextBlock>
#include <QPointer>
#include <QDebug>
class Browser : public QTextBrowser
{
QPointer<QMenu> m_menu;
protected:
void contextMenuEvent(QContextMenuEvent *ev) {
Q_ASSERT(m_menu.isNull()); // make sure the menus aren't leaking
m_menu = createStandardContextMenu();
QTextCursor cur = cursorForPosition(ev->pos());
QTextCharFormat fmt = cur.charFormat();
qDebug() << "position in block" << cur.positionInBlock()
<< "object type" << cur.charFormat().objectType();
if (fmt.objectType() == QTextFormat::NoObject) {
// workaround, sometimes the cursor will point one object to the left of the image
cur.movePosition(QTextCursor::NextCharacter);
fmt = cur.charFormat();
}
if (fmt.isImageFormat()) {
QTextImageFormat ifmt = fmt.toImageFormat();
m_menu->addAction(QString("Image URL: %1").arg(ifmt.name()));
}
m_menu->move(ev->globalPos());
m_menu->setAttribute(Qt::WA_DeleteOnClose); // the menu won't leak
m_menu->show(); // show the menu asynchronously so as not to block the application
}
};
void addImage(QTextDocument * doc, const QString & url) {
QImage img(100, 100, QImage::Format_ARGB32_Premultiplied);
img.fill(Qt::white);
QPainter p(&img);
p.drawRect(0, 0, 99, 99);
p.drawText(img.rect(), url);
doc->addResource(QTextDocument::ImageResource, QUrl(url), img);
}
int main(int argc, char *argv[])
{
QApplication a(argc, argv);
QTextDocument doc;
Browser browser;
doc.setHtml("<img src=\"data://image1\"/><br/><img src=\"data://image2\"/>");
addImage(&doc, "data://image1");
addImage(&doc, "data://image2");
browser.show();
browser.setDocument(&doc);
return a.exec();
}
Maybe someone can help me with the following problem:
I want to draw the content of a QImage in a QGLWidget, but the widget is painted in black.
class QGLCanvas {
public:
QGLCanvas(QWidget* parent) : QGLWidget(parent) {
}
void setImage(const QImage* image) {
img = image;
}
void paintEvent(QPaintEvent*) {
// From Painter Documentation Qt
QPainter p(this);
p.setRenderHint(QPainter::SmoothPixmapTransform, 1);
p.drawImage(this->rect(), *img);
p.end();
}
public slots:
void rgb_data(const void *data) {
memcpy((void *)img->bits(), data, img->byteCount()); // data will be copied (sizes are known)
// img.save("text.png"); // saves right image
this->update(); // calls repaint, but does not draw the image.
}
private:
QImage *img;
}
The Bug:
When the slot is called, the memory is copied to the image. If the image is saved, the content is correct. But the repaint method just draws black content to the widget.
The Fix:
If the memcpy line is implemented outside the slot, the image content is drawn to the widget. This fix increased code complexity a lot. Thus, i've got the following question:
The Question:
Why does the memcpy not work within the slot? Is this a general problem with Qt?
There's nothing special about a slot which would stop your code from working.
What's probably the issue is that when you call update(), a repaint is scheduled but happens asynchronously. From the code you've provided the most likely cause is img being modified between the calls to rbg_data and paintEvent
You want to be sure about the format of the QImage. When you call bits and are expecting it to be RGB, you need to check the format.
if( img->format() != QImage::Format_RGB888 )
{
// convert the image format to RGB888
*img = img->convertToFormat(QImage::Format_RGB888);
}
This way, Qt will know the image format when trying to paint it. If you fill it with RGB data but the QImage is "formatted" as ARGB, you will get some painting errors.
I'm trying to animate the change of a QPixmap, inside QLabel.
I have MainWindow which holds several objects that derive from QScrollArea. Each of these holds a QLabel member.
Using mousePressEvent() I am able to replace the picture of each QLabel using setPixmap(). However, that simply switches the image in each QLabel, while what I would like to achieve is an animation where a new image slides over the existing one.
First I tried using a QTimeLine to draw the QPixmap on the QLabel myself (I've created a class that derives from QLabel for that, and wrote my own setPixmap()) but that didn't work. Next I tried using QPropertyAnimation but it can't construct on a Pixmap without me implementing a sub class for that as well.
Any thoughts or ideas are appreciated.
You will need a QObject with a property that can be animated, and generates the intermediate frames for the animation. An incomplete example:
class LabelAnimator : public QObject
{
Q_OBJECT
Q_PROPERTY(float progress READ progress WRITE setProgress)
public:
LabelAnimator(QLabel* label) : mProgress(0.0f),
mLabel(label),
mAnimation(new QPropertyAnimation(this, "progress", this)
{
mAnimation->setStartValue(0.0f);
mAnimation->setEndValue(1.0f);
}
void setProgress(float progress) {
mProgress = progress;
QPixmap pix = mOriginalPixmap;
int offset = - mLabel->width() * (1.0f-progress);
QPainter painter(&pix);
painter.paint(off, 0, mNewPixmap);
painter.end();
mLabel->setPixmap(pix);
}
void setPixmap(const QPixmap& pix) {
mOriginalPixmap = mLabel->pixmap();
mNewPixmap = pix;
mAnimation->start();
}
};
QLabel was never designed for such uses. Draw your QPixmaps inside a QGraphicsView, it is far more focused towards rendering effects and animations.