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本章来学习下漫游相机。

路径动画与相机漫游

本届内容比较简单，其实就是实现物体的运动和相机的运动

当然这两个要一起执行。

贝塞尔曲线

贝塞尔曲线（Bézier curve）是一种在计算机图形学、动画制作、工业设计等领域广泛应用的参数曲线，它由法国工程师皮埃尔・贝塞尔（Pierre Bézier）在 20 世纪 60 年代为汽车工业设计而提出。

大致类似这样：

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通过控制一些点来定义整个曲线。

实战

使用OpenSceneGraph（OSG）实现沿贝塞尔曲线移动模型以及录制相机路径的示例代码。

代码实现了在OSG中创建一个模型，并让它沿着贝塞尔曲线移动，同时也记录相机的路径。

#include <osg/Group>
#include <osg/Node>
#include <osg/Geometry>
#include <osg/Geode>
#include <osgViewer/Viewer>
#include <osgGA/TrackballManipulator>
#include <osg/MatrixTransform>
#include <osg/AnimationPath>
#include <osg/Quat>
#include <iostream>
#include <vector>// 计算贝塞尔曲线上的点
osg::Vec3 bezierPoint(const std::vector<osg::Vec3>& controlPoints, double t) {int n = controlPoints.size() - 1;osg::Vec3 result(0.0, 0.0, 0.0);for (int i = 0; i <= n; ++i) {double binomial = 1.0;for (int j = 0; j < i; ++j) {binomial *= (n - j) / (i - j);}binomial *= pow(1 - t, n - i) * pow(t, i);result += binomial * controlPoints[i];}return result;
}int main() {// 创建一个场景组osg::ref_ptr<osg::Group> root = new osg::Group;// 创建一个简单的模型（这里以一个立方体为例）osg::ref_ptr<osg::Geometry> geom = osg::createTexturedCubeGeometry(osg::Vec3(0, 0, 0), 1.0);osg::ref_ptr<osg::Geode> geode = new osg::Geode;geode->addDrawable(geom);root->addChild(geode);// 贝塞尔曲线的控制点std::vector<osg::Vec3> controlPoints = {osg::Vec3(-5, 0, 0),osg::Vec3(-2, 5, 0),osg::Vec3(2, -5, 0),osg::Vec3(5, 0, 0)};// 创建动画路径osg::ref_ptr<osg::AnimationPath> animationPath = new osg::AnimationPath;animationPath->setLoopMode(osg::AnimationPath::LOOP);// 采样贝塞尔曲线生成动画路径的关键帧const int numSamples = 100;for (int i = 0; i < numSamples; ++i) {double t = static_cast<double>(i) / (numSamples - 1);osg::Vec3 position = bezierPoint(controlPoints, t);osg::Quat orientation; // 这里简单设置为无旋转osg::Vec3 scale(1, 1, 1);osg::AnimationPath::ControlPoint cp(static_cast<double>(i) * 0.1, position, orientation, scale);animationPath->insert(cp);}// 创建一个矩阵变换节点来应用动画路径osg::ref_ptr<osg::MatrixTransform> mt = new osg::MatrixTransform;mt->addChild(geode);osg::ref_ptr<osg::AnimationPathCallback> callback = new osg::AnimationPathCallback(animationPath);mt->setUpdateCallback(callback);root->addChild(mt);// 创建相机路径记录器osg::ref_ptr<osg::Group> cameraPathGroup = new osg::Group;osg::ref_ptr<osg::Vec3Array> cameraPathVertices = new osg::Vec3Array;osg::ref_ptr<osg::Geometry> cameraPathGeom = new osg::Geometry;cameraPathGeom->setVertexArray(cameraPathVertices);osg::ref_ptr<osg::Geode> cameraPathGeode = new osg::Geode;cameraPathGeode->addDrawable(cameraPathGeom);cameraPathGroup->addChild(cameraPathGeode);root->addChild(cameraPathGroup);// 创建查看器osgViewer::Viewer viewer;viewer.setSceneData(root);viewer.setCameraManipulator(new osgGA::TrackballManipulator);// 记录相机路径bool recording = false;osg::Vec3 lastCameraPosition;viewer.setCameraManipulator(new osgGA::TrackballManipulator);viewer.realize();while (!viewer.done()) {osg::Matrix cameraMatrix = viewer.getCamera()->getViewMatrix();osg::Vec3 cameraPosition = osg::Vec3(cameraMatrix.getTrans());if (recording) {cameraPathVertices->push_back(cameraPosition);osg::ref_ptr<osg::DrawArrays> drawArrays = new osg::DrawArrays(osg::PrimitiveSet::LINE_STRIP, 0, cameraPathVertices->size());cameraPathGeom->setDrawArray(drawArrays);}// 简单的按键控制记录开始和结束const osgGA::GUIEventAdapter& ea = viewer.getEventQueue()->getCurrentEvent();if (ea.getEventType() == osgGA::GUIEventAdapter::KEYDOWN && ea.getKey() == osgGA::GUIEventAdapter::KEY_R) {recording =!recording;if (recording) {lastCameraPosition = cameraPosition;}}viewer.frame();}return 0;
}