How I can find a particular item in the scene and remove it .
I have declared a graphicsitem and added it to the scene. Now in certain case I have to remove the item from the scene but before removing the item from the scene I want to know the item is added to scene or not. If I try to remove the item which is not added to the scene, I get the below error:
"QGraphicsScene::removeItem: item 0x121c520's scene (0x0) is different from this scene (0x1143850)"
the item is not selected so I can not use the scene()->selectedItem() list.
You can check the pointer returned from calling QGraphicsItem::scene(). It will either return the scene, or NULL if it is not present in a scene.
// assuming item is a class derived from QGraphicsItem
if(item->scene() != nullptr) // nullptr from C++ 11, else use NULL
{
// item is in a scene
}
Related
I have a function that draws triangles through OpenGL
I draw two triangles by pressing a button (function on_drawMapPushButton_clicked()).
Then i draw a sphere that placed above these triangles. And now i see, that sphere is drawed correctly over first triangle, but second triangle drawed over the sphere and not vice versa.
If i press the button second time, then spehere is drawed correctly over first and second triangles.
When i press the button third time, then second triangle drawed over the sphere again.
When i press the button fourth time, then spehere is drawed correctly over first and second triangles and so on.
If i use in sphereMesh QPhongMaterial instead of QPhongAlphaMaterial, then spehere is drawed correctly over first and second triangles always. Like it must to be.
I can't understand what i do wrong to get my sphere is drawed always over the triangles.
Code, that draws transparent sphere:
selectModel_ = new Qt3DExtras::QSphereMesh(selectEntity_);
selectModel_->setRadius(75);
selectModel_->setSlices(150);
selectMaterial_ = new Qt3DExtras::QPhongAlphaMaterial(selectEntity_);
selectMaterial_->setAmbient(QColor(28, 61, 136));
selectMaterial_->setDiffuse(QColor(11, 56, 159));
selectMaterial_->setSpecular(QColor(10, 67, 199));
selectMaterial_->setShininess(0.8f);
selectEntity_->addComponent(selectModel_);
selectEntity_->addComponent(selectMaterial_);
Function drawTriangles:
void drawTriangles(QPolygonF triangles, QColor color){
int numOfVertices = triangles.size();
// Create and fill vertex buffer
QByteArray bufferBytes;
bufferBytes.resize(3 * numOfVertices * static_cast<int>(sizeof(float)));
float *positions = reinterpret_cast<float*>(bufferBytes.data());
for(auto point : triangles){
*positions++ = static_cast<float>(point.x());
*positions++ = 0.0f; //We need to drow only on the surface
*positions++ = static_cast<float>(point.y());
}
geometry_ = new Qt3DRender::QGeometry(mapEntity_);
auto *buf = new Qt3DRender::QBuffer(geometry_);
buf->setData(bufferBytes);
positionAttribute_ = new Qt3DRender::QAttribute(mapEntity_);
positionAttribute_->setName(Qt3DRender::QAttribute::defaultPositionAttributeName());
positionAttribute_->setVertexBaseType(Qt3DRender::QAttribute::Float); //In our buffer we will have only floats
positionAttribute_->setVertexSize(3); // Size of a vertex
positionAttribute_->setAttributeType(Qt3DRender::QAttribute::VertexAttribute); // Attribute type
positionAttribute_->setByteStride(3 * sizeof(float));
positionAttribute_->setBuffer(buf);
geometry_->addAttribute(positionAttribute_); // Add attribute to ours Qt3DRender::QGeometry
// Create and fill an index buffer
QByteArray indexBytes;
indexBytes.resize(numOfVertices * static_cast<int>(sizeof(unsigned int))); // start to end
unsigned int *indices = reinterpret_cast<unsigned int*>(indexBytes.data());
for(unsigned int i = 0; i < static_cast<unsigned int>(numOfVertices); ++i) {
*indices++ = i;
}
auto *indexBuffer = new Qt3DRender::QBuffer(geometry_);
indexBuffer->setData(indexBytes);
indexAttribute_ = new Qt3DRender::QAttribute(geometry_);
indexAttribute_->setVertexBaseType(Qt3DRender::QAttribute::UnsignedInt); //In our buffer we will have only unsigned ints
indexAttribute_->setAttributeType(Qt3DRender::QAttribute::IndexAttribute); // Attribute type
indexAttribute_->setBuffer(indexBuffer);
indexAttribute_->setCount(static_cast<unsigned int>(numOfVertices)); // Set count of our vertices
geometry_->addAttribute(indexAttribute_); // Add the attribute to ours Qt3DRender::QGeometry
shape_ = new Qt3DRender::QGeometryRenderer(mapEntity_);
shape_->setPrimitiveType(Qt3DRender::QGeometryRenderer::Triangles);
shape_->setGeometry(geometry_);
//Create material
material_ = new Qt3DExtras::QPhongMaterial(mapEntity_);
material_->setAmbient(color);
trianglesEntity_ = new Qt3DCore::QEntity(mapEntity_);
trianglesEntity_->addComponent(shape_);
trianglesEntity_->addComponent(material_);
}
Press button handler on_drawMapPushButton_clicked():
void on_drawMapPushButton_clicked()
{
clearMap(); //Implementation is above
QPolygonF triangle1;
triangle1 << QPointF( 0 ,-1000) << QPointF(0 ,1000) << QPointF(1000, -1000);
drawTriangles(triangle1, Qt::black);
QPolygonF triangle2;
triangle2 << QPointF(-1000,-1000) << QPointF(-100,1000) << QPointF(-100,-1000);
drawTriangles(triangle2, Qt::red);
}
Map clearing function clearMap():
void clearMap()
{
if(mapEntity_){
delete mapEntity_;
mapEntity_ = nullptr;
mapEntity_ = new Qt3DCore::QEntity(view3dRootEntity_);
}
}
Ok here comes the extend answer.
The reason why this sometimes happens and sometimes not depends on the order of your entities. If you experiment with two simple spheres, one transparent and one not, you will see that when the sphere that is transparent is added later it will be drawn above the opaque object - just like you want it to.
This happens because the opaque object will be drawn first (it comes first in the scene graph) and the transparent object later which will give you the result you want. In the other case where the transparent object gets drawn first, the opaque object is drawn above because the QPhongAlphaMaterial has a QNoDepthMask render state which tells it not to write to the depth buffer. Thus, the opaque object always passes the depth test, where the transparent object actually already drew to. You have to do some more work to properly draw transparent objects for arbitrary scene graphs and camera positions.
The Qt3D Rendering Graph
To understand what you have to do you should understand how the Qt3D rendering graph is laid out. If you know this already you can skip this part.
Italic words reference items in the graph image in the following text.
If you use a Qt3DWindow, you can't access the root node of rendering graph. It is maintained by the window. You can access the QRenderSettings and root node of your framegraph through the functions activeFramegraph() and renderSettings() which you can both call on the window. You can also set the root node of scene graph through the setRootEntity() function of Qt3DWindow. The window internally has a QAspectEngine, where it sets the root node of the whole graph, which is the root node of the rendering graph in the graph image above.
If you want to insert a framegraph node to the existing framegraph of the 3D window, you have to add it as the parent of the active framegraph which I will explain in the next section. If you have your own custom framegraph which you set on the window through setActiveFramegraph() then just append it to the end, this should suffice.
Using QSortPolicy
As you already found out according to you other questions, you can use QSortPolicy in your framegraph to sort the entities by distance to camera. You can add a sort policy as follows (assuming that view is your Qt3DWindow and scene is your root entity of the scene graph, although I don't understand why it has to be):
Qt3DRender::QFrameGraphNode *framegraph = view.activeFrameGraph();
Qt3DRender::QSortPolicy *sortPolicy = new Qt3DRender::QSortPolicy(scene);
framegraph->setParent(sortPolicy);
QVector<Qt3DRender::QSortPolicy::SortType> sortTypes =
QVector<Qt3DRender::QSortPolicy::SortType>() << Qt3DRender::QSortPolicy::BackToFront;
sortPolicy->setSortTypes(sortTypes);
view.setActiveFrameGraph(framegraph);
The issue with this code is that this sort policy sorts the entities by the distance of their centers to the camera. If one of the opaque objects is closer to the camera than the transparent object it gets drawn later anyways and occludes the transparent object. See the images below for a graphical explanation.
The red and black sphere are further away from the camera than the torus, that's why they get drawn first and they don't occlude the torus.
No the center of the red sphere is closer to the camera than the center of the torus. It gets rendered later than the torus and occludes it.
Using Two Framegraph Branches
You can tackle the issue above if you use two framegraph branches. One which draws all opaque entities and one which draws all transparent ones. To achieve this you have to make use of QLayer and QLayerFilter. You can attach layers to entities and then add layer filters to your framegraph. This way you can exclude entities from entering a certain branch of your framegraph.
Let's say you create two layers, one for opaque objects and one for transparents ones:
Qt3DRender::QLayer *transparentLayer = new Qt3DRender::QLayer;
Qt3DRender::QLayer *opaqueLayer = new Qt3DRender::QLayer;
You have to attach the transparent layer to each transparent object and the opaque layer to each opaque object as a component (using addComponent()).
Unfortunately, you need a special framegraph tree to include the two corresponding layer filters (again, assuming that view is your Qt3DWindow):
Qt3DRender::QRenderSurfaceSelector *renderSurfaceSelector
= new Qt3DRender::QRenderSurfaceSelector();
renderSurfaceSelector->setSurface(&view);
Qt3DRender::QClearBuffers *clearBuffers
= new Qt3DRender::QClearBuffers(renderSurfaceSelector);
clearBuffers->setBuffers(Qt3DRender::QClearBuffers::AllBuffers);
clearBuffers->setClearColor(Qt::white);
This is the first branch to clear the buffers. Now you add the following code:
Qt3DRender::QViewport *viewport = new Qt3DRender::QViewport(renderSurfaceSelector);
Qt3DRender::QCameraSelector *cameraSelector = new Qt3DRender::QCameraSelector(viewport);
Qt3DRender::QCamera *camera = new Qt3DRender::QCamera(cameraSelector);
// set your camera parameters here
cameraSelector->setCamera(camera);
Since you create the QViewport as a child of the QRenderSurfaceSelector it is now a sibling in your framegraph with respect to the QClearBuffers. You can see an illustration of the example framegraphs here.
Now you have to create the two leaf nodes that contain the layer filters. The Qt3D engine always executes a whole branch when it reaches a leaf. This means that first the opaque objects are drawn and then the transparent ones.
// not entirely sure why transparent filter has to go first
// I would have expected the reversed order of the filters but this works...
Qt3DRender::QLayerFilter *transparentFilter = new Qt3DRender::QLayerFilter(camera);
transparentFilter->addLayer(transparentLayer);
Qt3DRender::QLayerFilter *opaqueFilter = new Qt3DRender::QLayerFilter(camera);
opaqueFilter->addLayer(opaqueLayer);
The two layer filters are now leaf nodes in your framegraph branch and Qt3D will first draw the opaque objects and then afterwards, since it uses the same viewport and everything, will draw the transparent objects above. It will draw them correctly (i.e. not in front of parts of opaque objects that the transparent object actually lies behind, because we did not clear the depth buffers again -> Splitting the framegraph happens only on the camera node).
Now set the new framegaph on your Qt3DWindow:
view.setActiveFrameGraph(renderSurfaceSelector);
Result:
Edit (26.03.21): As Patrick B. pointed out correctly, using the suggested solution with two layers you will have to add both layers as components to any lights in the scene. You can get around this by setting the filter mode on the QLayerFilters to QLayerFilter::FilterMode::DiscardAnyMatching and then reverse the order of the filters. This way, the transparentFilter discards any entities with the transparentLayer attached - but not the lights because they don't have the transparentLayer. Vice versa for the opaqueFilter.
My mistake was that i did wrong order of creating and deletion of Triangles and Sphere entities.
In pseudo code right order is as follows:
clearTriangles();
clearSphere();
drawTriangles();
drawSphere();
If you are using Qt3d with QML and want to control the order elements are drawn you can control it by the order of layers in your QML file.
Something like:
{
objectName: "firstLayer"
id : firstLayer
}
Layer {
objectName: "secondLayer"
id: secondLayer
}
The order you add them to layer filters will then control which is drawn first:
RenderSurfaceSelector {
CameraSelector {
id : cameraSelector
camera: mainCamera
FrustumCulling {
ClearBuffers {
buffers : ClearBuffers.AllBuffers
clearColor: "#04151c"
NoDraw {}
}
LayerFilter
{
objectName: "firstLayerFilter"
id: firstLayerFilter
layers: [firstLayer]
}
LayerFilter
{
id: secondLayerFilter
objectName: "secondLayerFilter"
layers: [secondLayer]
}
Then anything you add to the secondLayer will get drawn over-top of the first layer. I used this to make sure text always showed up in front of shapes, but it can be used similarly with transparencies.
I have a function that draws triangles through OpenGL
I draw two triangles by pressing a button (function on_drawMapPushButton_clicked()).
Then i draw a sphere that placed above these triangles. And now i see, that sphere is drawed correctly over first triangle, but second triangle drawed over the sphere and not vice versa.
If i press the button second time, then spehere is drawed correctly over first and second triangles.
When i press the button third time, then second triangle drawed over the sphere again.
When i press the button fourth time, then spehere is drawed correctly over first and second triangles and so on.
If i use in sphereMesh QPhongMaterial instead of QPhongAlphaMaterial, then spehere is drawed correctly over first and second triangles always. Like it must to be.
I can't understand what i do wrong to get my sphere is drawed always over the triangles.
Code, that draws transparent sphere:
selectModel_ = new Qt3DExtras::QSphereMesh(selectEntity_);
selectModel_->setRadius(75);
selectModel_->setSlices(150);
selectMaterial_ = new Qt3DExtras::QPhongAlphaMaterial(selectEntity_);
selectMaterial_->setAmbient(QColor(28, 61, 136));
selectMaterial_->setDiffuse(QColor(11, 56, 159));
selectMaterial_->setSpecular(QColor(10, 67, 199));
selectMaterial_->setShininess(0.8f);
selectEntity_->addComponent(selectModel_);
selectEntity_->addComponent(selectMaterial_);
Function drawTriangles:
void drawTriangles(QPolygonF triangles, QColor color){
int numOfVertices = triangles.size();
// Create and fill vertex buffer
QByteArray bufferBytes;
bufferBytes.resize(3 * numOfVertices * static_cast<int>(sizeof(float)));
float *positions = reinterpret_cast<float*>(bufferBytes.data());
for(auto point : triangles){
*positions++ = static_cast<float>(point.x());
*positions++ = 0.0f; //We need to drow only on the surface
*positions++ = static_cast<float>(point.y());
}
geometry_ = new Qt3DRender::QGeometry(mapEntity_);
auto *buf = new Qt3DRender::QBuffer(geometry_);
buf->setData(bufferBytes);
positionAttribute_ = new Qt3DRender::QAttribute(mapEntity_);
positionAttribute_->setName(Qt3DRender::QAttribute::defaultPositionAttributeName());
positionAttribute_->setVertexBaseType(Qt3DRender::QAttribute::Float); //In our buffer we will have only floats
positionAttribute_->setVertexSize(3); // Size of a vertex
positionAttribute_->setAttributeType(Qt3DRender::QAttribute::VertexAttribute); // Attribute type
positionAttribute_->setByteStride(3 * sizeof(float));
positionAttribute_->setBuffer(buf);
geometry_->addAttribute(positionAttribute_); // Add attribute to ours Qt3DRender::QGeometry
// Create and fill an index buffer
QByteArray indexBytes;
indexBytes.resize(numOfVertices * static_cast<int>(sizeof(unsigned int))); // start to end
unsigned int *indices = reinterpret_cast<unsigned int*>(indexBytes.data());
for(unsigned int i = 0; i < static_cast<unsigned int>(numOfVertices); ++i) {
*indices++ = i;
}
auto *indexBuffer = new Qt3DRender::QBuffer(geometry_);
indexBuffer->setData(indexBytes);
indexAttribute_ = new Qt3DRender::QAttribute(geometry_);
indexAttribute_->setVertexBaseType(Qt3DRender::QAttribute::UnsignedInt); //In our buffer we will have only unsigned ints
indexAttribute_->setAttributeType(Qt3DRender::QAttribute::IndexAttribute); // Attribute type
indexAttribute_->setBuffer(indexBuffer);
indexAttribute_->setCount(static_cast<unsigned int>(numOfVertices)); // Set count of our vertices
geometry_->addAttribute(indexAttribute_); // Add the attribute to ours Qt3DRender::QGeometry
shape_ = new Qt3DRender::QGeometryRenderer(mapEntity_);
shape_->setPrimitiveType(Qt3DRender::QGeometryRenderer::Triangles);
shape_->setGeometry(geometry_);
//Create material
material_ = new Qt3DExtras::QPhongMaterial(mapEntity_);
material_->setAmbient(color);
trianglesEntity_ = new Qt3DCore::QEntity(mapEntity_);
trianglesEntity_->addComponent(shape_);
trianglesEntity_->addComponent(material_);
}
Press button handler on_drawMapPushButton_clicked():
void on_drawMapPushButton_clicked()
{
clearMap(); //Implementation is above
QPolygonF triangle1;
triangle1 << QPointF( 0 ,-1000) << QPointF(0 ,1000) << QPointF(1000, -1000);
drawTriangles(triangle1, Qt::black);
QPolygonF triangle2;
triangle2 << QPointF(-1000,-1000) << QPointF(-100,1000) << QPointF(-100,-1000);
drawTriangles(triangle2, Qt::red);
}
Map clearing function clearMap():
void clearMap()
{
if(mapEntity_){
delete mapEntity_;
mapEntity_ = nullptr;
mapEntity_ = new Qt3DCore::QEntity(view3dRootEntity_);
}
}
Ok here comes the extend answer.
The reason why this sometimes happens and sometimes not depends on the order of your entities. If you experiment with two simple spheres, one transparent and one not, you will see that when the sphere that is transparent is added later it will be drawn above the opaque object - just like you want it to.
This happens because the opaque object will be drawn first (it comes first in the scene graph) and the transparent object later which will give you the result you want. In the other case where the transparent object gets drawn first, the opaque object is drawn above because the QPhongAlphaMaterial has a QNoDepthMask render state which tells it not to write to the depth buffer. Thus, the opaque object always passes the depth test, where the transparent object actually already drew to. You have to do some more work to properly draw transparent objects for arbitrary scene graphs and camera positions.
The Qt3D Rendering Graph
To understand what you have to do you should understand how the Qt3D rendering graph is laid out. If you know this already you can skip this part.
Italic words reference items in the graph image in the following text.
If you use a Qt3DWindow, you can't access the root node of rendering graph. It is maintained by the window. You can access the QRenderSettings and root node of your framegraph through the functions activeFramegraph() and renderSettings() which you can both call on the window. You can also set the root node of scene graph through the setRootEntity() function of Qt3DWindow. The window internally has a QAspectEngine, where it sets the root node of the whole graph, which is the root node of the rendering graph in the graph image above.
If you want to insert a framegraph node to the existing framegraph of the 3D window, you have to add it as the parent of the active framegraph which I will explain in the next section. If you have your own custom framegraph which you set on the window through setActiveFramegraph() then just append it to the end, this should suffice.
Using QSortPolicy
As you already found out according to you other questions, you can use QSortPolicy in your framegraph to sort the entities by distance to camera. You can add a sort policy as follows (assuming that view is your Qt3DWindow and scene is your root entity of the scene graph, although I don't understand why it has to be):
Qt3DRender::QFrameGraphNode *framegraph = view.activeFrameGraph();
Qt3DRender::QSortPolicy *sortPolicy = new Qt3DRender::QSortPolicy(scene);
framegraph->setParent(sortPolicy);
QVector<Qt3DRender::QSortPolicy::SortType> sortTypes =
QVector<Qt3DRender::QSortPolicy::SortType>() << Qt3DRender::QSortPolicy::BackToFront;
sortPolicy->setSortTypes(sortTypes);
view.setActiveFrameGraph(framegraph);
The issue with this code is that this sort policy sorts the entities by the distance of their centers to the camera. If one of the opaque objects is closer to the camera than the transparent object it gets drawn later anyways and occludes the transparent object. See the images below for a graphical explanation.
The red and black sphere are further away from the camera than the torus, that's why they get drawn first and they don't occlude the torus.
No the center of the red sphere is closer to the camera than the center of the torus. It gets rendered later than the torus and occludes it.
Using Two Framegraph Branches
You can tackle the issue above if you use two framegraph branches. One which draws all opaque entities and one which draws all transparent ones. To achieve this you have to make use of QLayer and QLayerFilter. You can attach layers to entities and then add layer filters to your framegraph. This way you can exclude entities from entering a certain branch of your framegraph.
Let's say you create two layers, one for opaque objects and one for transparents ones:
Qt3DRender::QLayer *transparentLayer = new Qt3DRender::QLayer;
Qt3DRender::QLayer *opaqueLayer = new Qt3DRender::QLayer;
You have to attach the transparent layer to each transparent object and the opaque layer to each opaque object as a component (using addComponent()).
Unfortunately, you need a special framegraph tree to include the two corresponding layer filters (again, assuming that view is your Qt3DWindow):
Qt3DRender::QRenderSurfaceSelector *renderSurfaceSelector
= new Qt3DRender::QRenderSurfaceSelector();
renderSurfaceSelector->setSurface(&view);
Qt3DRender::QClearBuffers *clearBuffers
= new Qt3DRender::QClearBuffers(renderSurfaceSelector);
clearBuffers->setBuffers(Qt3DRender::QClearBuffers::AllBuffers);
clearBuffers->setClearColor(Qt::white);
This is the first branch to clear the buffers. Now you add the following code:
Qt3DRender::QViewport *viewport = new Qt3DRender::QViewport(renderSurfaceSelector);
Qt3DRender::QCameraSelector *cameraSelector = new Qt3DRender::QCameraSelector(viewport);
Qt3DRender::QCamera *camera = new Qt3DRender::QCamera(cameraSelector);
// set your camera parameters here
cameraSelector->setCamera(camera);
Since you create the QViewport as a child of the QRenderSurfaceSelector it is now a sibling in your framegraph with respect to the QClearBuffers. You can see an illustration of the example framegraphs here.
Now you have to create the two leaf nodes that contain the layer filters. The Qt3D engine always executes a whole branch when it reaches a leaf. This means that first the opaque objects are drawn and then the transparent ones.
// not entirely sure why transparent filter has to go first
// I would have expected the reversed order of the filters but this works...
Qt3DRender::QLayerFilter *transparentFilter = new Qt3DRender::QLayerFilter(camera);
transparentFilter->addLayer(transparentLayer);
Qt3DRender::QLayerFilter *opaqueFilter = new Qt3DRender::QLayerFilter(camera);
opaqueFilter->addLayer(opaqueLayer);
The two layer filters are now leaf nodes in your framegraph branch and Qt3D will first draw the opaque objects and then afterwards, since it uses the same viewport and everything, will draw the transparent objects above. It will draw them correctly (i.e. not in front of parts of opaque objects that the transparent object actually lies behind, because we did not clear the depth buffers again -> Splitting the framegraph happens only on the camera node).
Now set the new framegaph on your Qt3DWindow:
view.setActiveFrameGraph(renderSurfaceSelector);
Result:
Edit (26.03.21): As Patrick B. pointed out correctly, using the suggested solution with two layers you will have to add both layers as components to any lights in the scene. You can get around this by setting the filter mode on the QLayerFilters to QLayerFilter::FilterMode::DiscardAnyMatching and then reverse the order of the filters. This way, the transparentFilter discards any entities with the transparentLayer attached - but not the lights because they don't have the transparentLayer. Vice versa for the opaqueFilter.
My mistake was that i did wrong order of creating and deletion of Triangles and Sphere entities.
In pseudo code right order is as follows:
clearTriangles();
clearSphere();
drawTriangles();
drawSphere();
If you are using Qt3d with QML and want to control the order elements are drawn you can control it by the order of layers in your QML file.
Something like:
{
objectName: "firstLayer"
id : firstLayer
}
Layer {
objectName: "secondLayer"
id: secondLayer
}
The order you add them to layer filters will then control which is drawn first:
RenderSurfaceSelector {
CameraSelector {
id : cameraSelector
camera: mainCamera
FrustumCulling {
ClearBuffers {
buffers : ClearBuffers.AllBuffers
clearColor: "#04151c"
NoDraw {}
}
LayerFilter
{
objectName: "firstLayerFilter"
id: firstLayerFilter
layers: [firstLayer]
}
LayerFilter
{
id: secondLayerFilter
objectName: "secondLayerFilter"
layers: [secondLayer]
}
Then anything you add to the secondLayer will get drawn over-top of the first layer. I used this to make sure text always showed up in front of shapes, but it can be used similarly with transparencies.
I wanted to have an online monitoring system that could tell where the shape is currently, but am getting very weird coordinates of the item, also the dimensions of it get higher by 1 each time I create new one and drag it.
Initial position (map size is 751 by 751, checked by outputting to qDebug(), scene bound to yellow space) :
Dragging it to the left top corner.
As you can see in the beginning it was on (200;200), but after dragging it is on (-201;-196). After deleting it and creating new shape on the same position with the same properties, new shape can't be seen because it is outside of the map, which suggests that edits don't show correct data.
Here is the code of updating the edits:
void CallableGraphicsRectItem::mouseReleaseEvent(QGraphicsSceneMouseEvent* event)
{
QGraphicsRectItem::mouseReleaseEvent(event);
ptr->updateEdits(this);
}
Here is what I managed to cut down into updateEdits():
void MainWindow::updateEdits(QAbstractGraphicsShapeItem* item)
{
//stuff not related to scene
auto posReal = item->scenePos();
auto pos = posReal.toPoint();
//create QString from coordinates
QString coordinate;
coordinate.setNum(pos.x());
ui->leftXEdit->setText(coordinate);
coordinate.setNum(pos.y());
ui->upperYEdit->setText(coordinate);
//get width and height for rect, radius for circle
auto boundingRectReal = item->sceneBoundingRect();
auto boundingRect = boundingRectReal.toRect();
ui->widthEdit->setText(QString::number(boundingRect.width()));
//disables height edit for circles, not really relevant
if (!items[currentShapeIndex].isRect)
{
ui->heightEdit->setDisabled(true);
}
else
{
ui->heightEdit->setDisabled(false);
ui->heightEdit->setText(QString::number(boundingRect.height()));
}
}
Here is how I anchor the QGraphicsScene to the left top corner of the yellow area:
scene->setSceneRect(0, 0, mapSize.width() - 20, mapSize.height() - 20);
ui->graphicsView->setScene(scene);
How can I report the right data to the edits?
You're better off overriding the itemChange method and using the ItemPositionHasChanged notification. You have to set the ItemSendsGeometryChanges flag on the item so that it receives these notifications.
I'm not sure that your item's final position has been set when you're still in the mouseReleaseEvent method. Tracking it in itemChange will ensure that the data is valid, and this kind of thing is what it's for.
Also, note that "pos" is in the item's parent coordinates, and "boundingRect" is in the item's coordinate space. You should use "scenePos" and "sceneBoundingRect" if you want to be sure you're using scene coordinates. If the item doesn't have a parent, then "pos" and "scenePos" will return the same values, but "boundingRect" and "sceneBoundingRect" will generally differ.
Does anyone have a better way to constrain a child of a QGraphicsItem to a scene?
I have successfully properly constrained a parent QGraphicsItem to its scene by overriding itemChange, but now I need to do the same for the child QGraphicsItem.
Example Use-case:
This code works... for the most part. The only problem is the QGraphicsItem's velocity when hitting either side will affect its endstop position:
QVariant SizeGripItem::HandleItem::itemChange(GraphicsItemChange change,
const QVariant &value)
{
QPointF newPos = value.toPointF();
if (change == ItemPositionChange)
{
if(scene())
{
newPos.setY(pos().y()); // Y-coordinate is constant.
if(scenePos().x() < 0 ) //If child item is off the left side of the scene,
{
if (newPos.x() < pos().x()) // and is trying to move left,
{
newPos.setX(pos().x()); // then hold its position
}
}
else if( scenePos().x() > scene()->sceneRect().right()) //If child item is off the right side of the scene,
{
if (newPos.x() > pos().x()) //and is trying to move right,
{
newPos.setX(pos().x()); // then hold its position
}
}
}
}
return newPos;
}
For the parent item, I used:
newPos.setX(qMin(scRect.right(), qMax(newPos.x(), scRect.left())));
which worked perfectly, but I'm stumped as to how or if I could use that here.
First, to be specific, scenes effectively have no boundaries. What you're trying to do is constrain the item to the scene rectangle that you've set elsewhere.
The problem I see is in your use of scenePos. This is an ItemPositionChange; the item's scenePos hasn't been updated with the new position yet, so when you check for scenePos being out of the scene rect, you're really checking the result of the last position change, not the current one. Because of that, your item ends up just off the edge of the scene rectangle and then sticks there. How far off the edge depends on how fast you were moving the mouse, which dictates how much distance there is between ItemPositionChange notifications.
Instead, you need to compare the new position to the scene rectangle and then restrict the value that gets returned to be within the scene rectangle. You need the new position in scene coordinates to do the comparison, so you need something like:
QPoint new_scene_pos = mapToScene (new_pos);
if (new_scene_pos.x() < scene()->sceneRect().left())
{
new_scene_pos.setX (scene()->sceneRect().left());
new_pos = mapFromScene (new_scene_pos);
}
This isn't complete code, obviously, but these are the conversions and checks you need to do to keep it in on the left side. The right side is very similar, so just use the new_scene_pos for the comparison there.
Note that I didn't assume that the left edge of sceneRecT is at 0. I'm sure that's what you coded where you set the sceneRect, but using the actual left value rather than assuming it's 0 eliminates any problems if you end up later changing the range of scene coordinates you're planning to work with.
I used "left" instead of "x" on the sceneRect call just because it parallels using "right" for the other side. They're exactly the same, but I think it reads slightly better in this case.
I tried to add several items to QGraphicsScene, but after calling scene->addItem(new Bonus(Bonus::BonusType::coin, randPoint, pixels, parent)); in application output appears this message: QGraphicsScene::addItem: item has already been added to this scene.What I do wrong?
Code:
for(int i = 0; i < coinsCount; ) {
QPoint randPoint(random() % g->getWidth(),
random() % g->getHeight());
if(g->getType(randPoint) != Graph::wall && !usedPoints.contains(randPoint)) {
scene->addItem(new Bonus(Bonus::BonusType::coin, randPoint, pixels, parent));
usedPoints.push_back(randPoint);
i++;
}
}
You are passing a parent item. If the parent item is already added to the scene, setting it as a parent for the new item will add the latter to the scene as well.
The constructor runs before addItem() so by the time the latter is executed, the item is already in the scene.
Note that this implicitly adds this graphics item to the scene of the
parent. You should not add the item to the scene yourself.