I have a QGraphicScene object that I can save to a PNG file just fine as long as I haven't made any modifications like a scroll or a zoom on the item. After performing a scroll or a zoom, the saved image becomes small with a lot of transparent pixels filling in the desired dimensions. I'm thinking it has to do with needing to render the visible region of the QGraphicsView to the QImage that gets saved but I'm having trouble figuring this out.
Below is some of my code:
void myClass::saveSceneAsPNGImage(QString path, int width)
{
Scene->clearSelection();
double scaleFactor = (width / Scene->sceneRect().size().width());
QImage image(Scene->sceneRect().size().width() * scaleFactor,
Scene->sceneRect().size().height() * scaleFactor,
QImage::Format_ARGB32);
QPainter painter(&image);
painter.setRenderHint(QPainter::Antialiasing);
Scene->render(&painter);
image.save(path);
}
Related
I have overriden updatePaintNode in the following way to draw an OpenGL texture on a QQuickItem derived class called MyQQuickItem here.
QSGNode *MyQQuickItem::updatePaintNode(QSGNode * oldNode, QQuickItem::UpdatePaintNodeData * /*updatePaintNodeData*/)
{
QSGSimpleTextureNode * textureNode = static_cast<QSGSimpleTextureNode *>(oldNode);
if (!textureNode) {
textureNode = new QSGSimpleTextureNode();
}
QSize size(800, 800);
// myTextureId is a GLuint here
textureNode.reset(window()->createTextureFromId(myTextureId, size));
textureNode->setTexture(my_texture);
textureNode->markDirty(QSGBasicGeometryNode::DirtyMaterial);
QSizeF myiewport = boundingRect().size();
qreal xOffset = 0;
qreal yOffset = 10;
textureNode->setRect(xOffset, yOffset, myViewport.width(), myViewport.height());
return textureNode;
}
This renders the texture content well but covers the whole of my MyQQuickItem UI.
How can reduce the bottom margin of the texture to say fit 80% of the height of MyQQuickItem.
I want to render the texture to a portion of MyQQuickItem & leave the rest blank or black? Is that possible within updatePaintNode.
Note that the texture size is not the UI window size here. My texture size is 800 by 800. Whereas the UI window size is different and depends on the screen.
I found the answer to this:
Changing myViewport.height() gives the required end in Y direction one wishes to set. Similarly, changing myViewport.width() gives the required end in X direction one wishes to set.
4 parameters in TextureNode's setRect can stretch & fit the texture in the way one wishes within a portion of the QQuickItem.
I am creating some images rendering the contents of a QGraphicsScene.
My project requirement is that it should handle a canvas size of 10 ft by 8 inches. On screen, and scene size, that is 8640 x 576 pixels.
I can render it fine.
The thing is, the output images need to have 300 resolution.
That means, the rendered image will have a width of 36000, which is over 2^15 - 1 = 32767 pixels.....
The output is clipped - in the code below, I would get a QImage of correct expected size (36000) but the QGraphicsScene only renders to 32767 pixels.
That is confusing... I cannot explain the outcome - if the QImage limitations were 32767 pixels, then I should not be able to create one in the first place. But I checked and the QImage "sanity check" is much higher.
Once the image is created, I do not see anything in the code for rendering QGraphicsScene that would clip at any value....
This is a simple code that is trying to expose my problem.
It creates a QImage of required size, and fills with yellow (for control).
Then it renders a QGraphicsScene with blue background brush and a red rectangle close to the right margin.
If it works correctly, the result should be: an image of width 36000, blue with a tiny red rectangle at the far right.
But... as it is, the result is an image of width 36000, blue for the first 32766 pixels then yellow for the rest, no red rectangle.
#include <QApplication>
#include <QGraphicsView>
#include <QGraphicsRectItem>
#include <QPainter>
void printScene(QGraphicsScene* s, qreal ratio) {
qreal w = s->width() * ratio;
qreal h = s->height() * ratio;
QRectF target(0, 0, w, h);
QImage image = QImage(w, h, QImage::Format_ARGB32_Premultiplied);
image.fill(QColor(Qt::yellow).rgb());
QPainter painter;
painter.begin(&image);
s->render(&painter, target);
painter.end();
image.save("image.png");
}
int main(int argc, char *argv[]) {
QApplication app(argc, argv);
QGraphicsScene s;
s.setSceneRect(0, 0, 8640, 576);
s.setBackgroundBrush(Qt::blue);
QGraphicsView view(&s);
view.show();
QGraphicsRectItem* r = s.addRect(8530, 250, 100, 100);
r->setBrush(Qt::red);
qreal ratio = 300/72.;
printScene(&s, ratio);
return app.exec();
}
As seen in sample images, the QImage is created successfully, QGraphicsScene though only renders to 2^15 - 1... But I stepped through their code and I didn't see it stop....
(I also tried creating the original scene 36000 x something (and setting the ratio to 1), and it displays fine... it just won't render to QImage anything beyond 32767 pixels)
Am I missing some setting ? What could be the cause of the QGraphicsScene::render() to not render more ?
I would love to find out how I can render the size I want - width of 36000 pixels - or a reason why this is not possible.
I am running this in Windows 7, 32 bit Qt 5.5.1 or 4.7.4
I have found the reason for the clipping - and imagined 2 workarounds.
Why:
Stepping through the rendering code, the clip rect gets limited to 32767:
bool QRasterPaintEngine::setClipRectInDeviceCoords(const QRect &r, Qt::ClipOperation op)
{
Q_D(QRasterPaintEngine);
QRect clipRect = r & d->deviceRect;
...
}
Where deviceRect is set by
void QRasterPaintEnginePrivate::systemStateChanged()
{
deviceRectUnclipped = QRect(0, 0,
qMin(QT_RASTER_COORD_LIMIT, device->width()),
qMin(QT_RASTER_COORD_LIMIT, device->height()));
QRegion clippedDeviceRgn = systemClip & deviceRectUnclipped;
deviceRect = clippedDeviceRgn.boundingRect();
baseClip->setClipRegion(clippedDeviceRgn);
...
}
and
// This limitations comes from qgrayraster.c. Any higher and
// rasterization of shapes will produce incorrect results.
const int QT_RASTER_COORD_LIMIT = 32767;
Options:
1) Render to a max of 32767 and, if the target must be bigger, scale result. (should give slightly lower quality)
2) Create 2 images and combine them (I still need to figure that out but I think it is the better fix)
I'm implementing an image viewer on an embedded platform. The hardware is a sort of tablet and has a touch screen as input device. The Qt version I'm using is 5.4.3.
The QGraphicsView is used to display a QGraphicsScene which contains a QGraphicsPixmapItem. The QGraphicsPixmapItem containts the pixmap to display.
The relevant part of the code is the following:
void MyGraphicsView::pinchTriggered(QPinchGesture *gesture)
{
QPinchGesture::ChangeFlags changeFlags = gesture->changeFlags();
if (changeFlags & QPinchGesture::ScaleFactorChanged) {
currentStepScaleFactor = gesture->totalScaleFactor();
}
if (gesture->state() == Qt::GestureFinished) {
scaleFactor *= currentStepScaleFactor;
currentStepScaleFactor = 1;
return;
}
// Compute the scale factor based on the current pinch level
qreal sxy = scaleFactor * currentStepScaleFactor;
// Get the pointer to the currently displayed picture
QList<QGraphicsItem *> listOfItems = items();
QGraphicsItem* item = listOfItems.at(0);
// Scale the picture
item.setScale(sxy);
// Adapt the scene to the scaled picture
setSceneRect(scene()->itemsBoundingRect());
}
As result of the pinch, the pixmap is scaled starting from the top-left corner of the view.
How to scale the pixmap respect to the center of the QPinchGesture?
From The Docs
The item is scaled around its transform origin point, which by default is (0, 0). You can select a different transformation origin by calling setTransformOriginPoint().
That function takes in a QPoint so you would need to find out your centre point first then set the origin point.
void QGraphicsItem::setTransformOriginPoint(const QPointF & origin)
I want to creat a image that contain the QTextEdit.
And I write the following code to create the image.
QSize s = textEdit->frameSize();
QPixmap p(s);
textEdit->render(&p);
p.save("textContent.png", "PNG");
But it can not contain the invisible contents.(while the contents is too long in QTextEdit)
I wander if there is a way to create a image which contain all the content in QTextEidt. And how.
Thanks.
i think, you can do it like via QTextDocument * QTextEdit::document () to receive QTextDocument * of your QTextEdit, and then draw it to QImage via void QTextDocument::drawContents ( QPainter * p, const QRectF & rect = QRectF() )
It draws the content of the document with painter p, clipped to rect. If rect is a null rectangle (default) then the document is painted unclipped.
check man here - http://harmattan-dev.nokia.com/docs/library/html/qt4/qtextdocument.html#drawContents
Or - the other way - take all the text from TextEdit via toPlainHtml() or toPlainText() - what's more suitable for your needs and draw it to QImage via QPainter's method QPainter::DrawText()
I need to do something similar to QPainter::drawImage, but drawing a triangle part of the given picture (into a triangular region of my widget) instead of working with rectangles.
Any idea how I could do that, besides painfully trying to redraw every pixel?
Thanks for your insights!
If it is feasible for you to use a QPixmap instead of a QImage, you can set a bitmap mask for the QPixmap which defines which of the pixels are shown and which are transparent:
myPixmap->setMask(myTriangleMask);
painter->drawPixmap(myPixmap);
Here is another solution based on QImage:
MaskWidget::MaskWidget(QWidget* parent) : QWidget(parent) {
img = QImage("Sample.jpg"); // The image to paint
mask = QImage("Mask.png"); // An indexed 2-bit colormap image
QPainter imgPainter(&img);
imgPainter.drawImage(0, 0, mask); // Paint the mask onto the image
}
void MaskWidget::paintEvent ( QPaintEvent * event ) {
QPainter painter(this);
painter.drawImage(10, 10, img);
}
Mask.png is an image file with the same size as Sample.jpg. It contains an alpha channel to support transparency. You can create this file easily with The GIMP, for example. I added an alpha channel, changed all areas I want to have painted to transparent and all other areas to white. To reduce the size, I finally converted it to an indexed 2-bit image.
You could even create the mask image programmatically with Qt, if you need your triangle be computed based on various parameters.