How to create Undo/Redo operations in Qt3D? - qt

Question

I created some entities using qt3d in QML. For example, this code shows a Scene3D element that declares RootEntity which is another QML element that contains the scene graph:
Scene3D
{
id : scene3d
anchors.fill: parent
focus: true
aspects: ["render", "logic", "input"]
hoverEnabled: true
cameraAspectRatioMode: Scene3D.AutomaticAspectRatio
antialiasing: true
RootEntity
{
id:root
}
}
RootEntity.qml:
Entity {
id:root
property double x : 0.0
Camera {
id: mainCamera
projectionType: CameraLens.PerspectiveProjection
fieldOfView: 45
aspectRatio: 16/9
nearPlane : 0.1
farPlane : 1000.0
position: Qt.vector3d(0.0, 4.49373, -3.78577)
upVector: Qt.vector3d( 0.0, 1.0, 0.0 )
viewCenter: Qt.vector3d(0.0, 0.5, 0.0)
}
OrbitCameraController
{
id: mainCameraController
camera: mainCamera
}
components: [
RenderSettings {
Viewport {
normalizedRect: Qt.rect(0.0, 0.0, 1.0, 1.0)
RenderSurfaceSelector {
CameraSelector {
id: cameraSelector
camera: mainCamera
FrustumCulling {
ClearBuffers {
buffers: ClearBuffers.AllBuffers
clearColor: "#444449"
NoDraw {}
}
LayerFilter {
filterMode: LayerFilter.DiscardAnyMatchingLayers
layers: [topLayer]
}
LayerFilter {
filterMode: LayerFilter.AcceptAnyMatchingLayers
layers: [topLayer]
ClearBuffers {
buffers: ClearBuffers.DepthBuffer
}
}
}
}
}
}
},
InputSettings {}
]
Layer {
id: topLayer
recursive: true
}
ListModel {
id: entityModel
ListElement { x:0;y:0;z:0 }
}
NodeInstantiator
{
id:instance
model: entityModel
delegate: Entity {
id: sphereEntity
components: [
SphereMesh
{
id:sphereMesh
radius: 0.3
},
PhongMaterial
{
id: materialSphere
ambient:"red"
},
Transform {
id: transform
translation:Qt.vector3d(x, y, z)
}
]
}
}
MouseDevice
{
id: mouseDev
}
MouseHandler
{
id: mouseHandler
sourceDevice: mouseDev
onPressed:
{
x++;
entityModel.append({"x":x,"y":0.0,"z": Math.random()})
}
}
}
When the mouse is clicked in my Scene3D, one sphere is displayed.
I don't know how to delete a specific Entity or create undo/redo effect by hitting Ctrl+Z and Ctrl+Shift+Z in Qt3d.
Thanks.

Answer 1

One approach is to maintain a global list of Qt.vector3d elements and use it to record the position of the spheres that are removed with the "Undo" operation:
When the user hits CTRL+Z, create a new Qt.vector3d object to store the position of the last sphere rendered (that is, the one that was last appended to entityModel) and add that position to the global list of 3d vectors;
Then, to remove a sphere from the screen, call entityModel.remove() with the index of the sphere that needs to be erased;
The "Redo" operation simply does the opposite:
When the user hits CTRL+Y, the last element of the global list of 3d vectors holds the location of the lastest sphere removed: append this position to entityModel so the sphere can be rendered again;
Then, remember to erase this position from the global list so the next Undo operation can render a different sphere;
RootEntity.qml:
import QtQuick 2.0
import QtQml.Models 2.15
import Qt3D.Core 2.12
import Qt3D.Render 2.12
import Qt3D.Extras 2.12
import Qt3D.Input 2.12
Entity {
id: root
// global list of Qt.vector3d elements that store the location of the spheres that are removed
property variant removedSpheres : []
// x-coordinate of the next sphere that will be added
property double x : 0.0
Camera {
id: mainCamera
projectionType: CameraLens.PerspectiveProjection
fieldOfView: 45
aspectRatio: 16/9
nearPlane : 0.1
farPlane : 1000.0
position: Qt.vector3d(0.0, 4.49373, -3.78577)
upVector: Qt.vector3d( 0.0, 1.0, 0.0 )
viewCenter: Qt.vector3d(0.0, 0.5, 0.0)
}
OrbitCameraController {
id: mainCameraController
camera: mainCamera
}
components: [
RenderSettings {
Viewport {
normalizedRect: Qt.rect(0.0, 0.0, 1.0, 1.0)
RenderSurfaceSelector {
CameraSelector {
id: cameraSelector
camera: mainCamera
FrustumCulling {
ClearBuffers {
buffers: ClearBuffers.AllBuffers
clearColor: "#444449"
NoDraw {}
}
LayerFilter {
filterMode: LayerFilter.DiscardAnyMatchingLayers
layers: [topLayer]
}
LayerFilter {
filterMode: LayerFilter.AcceptAnyMatchingLayers
layers: [topLayer]
ClearBuffers {
buffers: ClearBuffers.DepthBuffer
}
}
}
}
}
}
},
InputSettings {}
]
Layer {
id: topLayer
recursive: true
}
ListModel {
id: entityModel
ListElement { x: 0; y: 0; z: 0 }
}
NodeInstantiator {
id: instance
model: entityModel
delegate: Entity {
id: sphereEntity
components: [
SphereMesh { id:sphereMesh; radius: 0.3 },
PhongMaterial { id: materialSphere; ambient:"red" },
Transform { id: transform; translation:Qt.vector3d(x, y, z) }
]
}
}
MouseDevice {
id: mouseDev
}
MouseHandler {
id: mouseHandler
sourceDevice: mouseDev
onPressed:
{
if (mouse.button === Qt.LeftButton)
{
console.log("LeftButton: new sphere")
// add new sphere
entityModel.append( {"x" : ++root.x, "y" : 0.0, "z" : Math.random()} )
}
if (mouse.button === Qt.MiddleButton)
{
console.log("MiddleButton: clear spheres")
// removes all spheres (can't be undone)
root.x = 0;
entityModel.clear();
removedSpheres.length = 0;
}
}
}
KeyboardDevice {
id: keyboardDev
}
KeyboardHandler {
id: keyboardHandler
sourceDevice: keyboardDev
focus: true
onPressed: {
// handle CTRL+Z: undo
if (event.key === Qt.Key_Z && (event.modifiers & Qt.ControlModifier))
{
console.log("CTRL+Z")
// remove the last sphere added to the screen
let lastIdx = entityModel.count - 1;
if (lastIdx >= 0)
{
// save sphere position before removal
removedSpheres.push(Qt.vector3d(entityModel.get(lastIdx).x, entityModel.get(lastIdx).y, entityModel.get(lastIdx).z));
// remove sphere from the model
entityModel.remove(lastIdx);
}
}
// handle CTRL+Y: redo
if (event.key === Qt.Key_Y && (event.modifiers & Qt.ControlModifier))
{
console.log("CTRL+Y")
// add the last sphere removed back into the model
if (removedSpheres.length > 0)
{
// add the sphere
let lastIdx = removedSpheres.length - 1;
entityModel.append( {"x" : removedSpheres[lastIdx].x, "y" : removedSpheres[lastIdx].y, "z" : removedSpheres[lastIdx].z} )
// erase the last item added to removedSpheres
removedSpheres.pop()
}
}
}
}
}