qml 3d模型运动，绘制轨迹图

要在QML中绘制3D模型的运动轨迹，可以使用Qt3D模块。以下是一个简单的示例，其中包含一个3D模型和其轨迹图：

import Qt3D.Core 2.12
import Qt3D.Render 2.12
import Qt3D.Input 2.12
import Qt3D.Extras 2.12

Entity {
    id: sceneRoot

    // 3D model
    Entity {
        id: modelEntity

        components: [
            // transform component to move the model
            Transform {
                id: modelTransform
                translation: Qt.vector3d(0, 0, -5)
            },
            // mesh component with a 3D model file
            Mesh {
                source: "models/myModel.obj"
            }
        ]
    }

    // trajectory line
    Entity {
        id: trajectoryEntity

        // array of points for the line
        property vector3d[] points: [
            Qt.vector3d(0, 0, -5),
            Qt.vector3d(1, 2, -7),
            Qt.vector3d(-3, 1, -9),
            Qt.vector3d(2, -1, -11)
        ]

        // component to draw the line
        LineRenderer {
            id: lineRenderer
            material: DefaultMaterial { lineWidth: 3 }
            primitiveType: LineRenderer.Lines
            geometry: Geometry {
                id: lineGeometry
                attributes: [
                    // position attribute
                    Attribute {
                        name: defaultAttributeNames.positionAttributeName
                        attributeType: Attribute.VertexAttribute
                        vertexBaseType: Attribute.Float
                        vertexSize: 3
                        byteOffset: 0
                        byteStride: 12
                        count: trajectoryEntity.points.length
                        buffer: Buffer {
                            id: lineVertexBuffer
                            type: Buffer.VertexBuffer
                            data: trajectoryEntity.points
                        }
                    }
                ]
            }
        }
    }

    // animation to move the model along the trajectory
    SequentialAnimation {
        id: animation

        NumberAnimation {
            target: modelTransform
            property: "translation.x"
            from: 0
            to: trajectoryEntity.points[0].x
            duration: 1000
        }
        NumberAnimation {
            target: modelTransform
            property: "translation.y"
            from: 0
            to: trajectoryEntity.points[0].y
            duration: 1000
        }
        NumberAnimation {
            target: modelTransform
            property: "translation.z"
            from: 0
            to: trajectoryEntity.points[0].z
            duration: 1000
        }

        // loop the animation through all the trajectory points
        onStopped: {
            var nextPoint = (animation.current + 1) % trajectoryEntity.points.length;
            animation.to = Qt.vector3d(
                trajectoryEntity.points[nextPoint].x,
                trajectoryEntity.points[nextPoint].y,
                trajectoryEntity.points[nextPoint].z
            );
            animation.start();
        }
    }

    // start the animation
    Component.onCompleted: {
        animation.to = Qt.vector3d(
            trajectoryEntity.points[1].x,
            trajectoryEntity.points[1].y,
            trajectoryEntity.points[1].z
        );
        animation.start();
    }
}

在此示例中，我们定义了一个3D场景，其中包含一个3D模型和一个轨迹图线。我们还创建了一个动画，该动画将模型沿着轨迹线移动，并在达到每个点时更新目标位置以循环动画。要绘制轨迹，我们使用了LineRenderer组件，该组件根据一组点在3D场景中绘制线条。