透視投影與正視投影圖：
正視投影正上方觀察牛的代碼：
#include <osg/Camera> #include <osgDB/ReadFile> #include <osgViewer/Viewer> osg::Camera* createBirdsEye( const osg::BoundingSphere& bs ) { osg::ref_ptr<osg::Camera> camera = new osg::Camera; camera->setClearMask( GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT ); camera->setReferenceFrame( osg::Transform::ABSOLUTE_RF ); double viewDistance = 2.0 * bs.radius(); double znear = viewDistance - bs.radius(); double zfar = viewDistance + bs.radius(); float top = bs.radius(); float right = bs.radius(); float bottom = top; float left = right; //osg左手系坐標(z+向上，x+向右，y+向里) camera->setProjectionMatrixAsOrtho( -left, right, -bottom, top, znear, zfar );//設置正投影 //牛的身長變短了（在視口大小沒有變化的情況下，加大left和right(原本是6.3),牛的左右相對於裁剪區域來說，就縮小了,我是這么理解。） //camera->setProjectionMatrixAsOrtho( -10, 10, -bottom, top, znear, zfar ); //牛的身長變窄了（同上理） //camera->setProjectionMatrixAsOrtho( -left, right, -20, 20, znear, zfar ); //改變了znear和zfar，好像沒什么變化，為什么呢，待找答案。**** //camera->setProjectionMatrixAsOrtho( -left, right, -bottom, top, 1, 1 ); /********* openGL解釋*************************************************************************** setProjectionMatrixAsOrtho(left,right,bottom,top,zNear,zFar); left和right表示最小和最大x值，top和bottom是最小和最大的y值，near和far是最小和最大的z值。 left：裁剪區域最左邊的坐標。 right:裁剪區域最右邊的坐標。 bottom：最底部的坐標。 top:最頂部的坐標。 near：從原點距離觀察者的最小位置。 far：從原點距離觀察者的最大位置。 **************************************************************************************************/ osg::Vec3d upDirection( 0.0,1.0,0.0 ); osg::Vec3d viewDirection( 0.0,0.0,1.0 ); osg::Vec3d center = bs.center(); osg::Vec3d eyePoint = center + viewDirection * viewDistance; //從前面看牛 //eyePoint.set(0.77,-10,0.5); //從牛頭看牛 //upDirection.set(0.0,0.0,1.0); //eyePoint.set(10,-0.4,0.5); //從牛下巴看牛 //upDirection.set(1.0,0.0,-1.0); //eyePoint.set(100,-0.4,-100); camera->setViewMatrixAsLookAt( eyePoint, center, upDirection );//相機位置（眼睛位置，眼睛看到的場景中心位置，視點向上的量） //eyePoint（0.77，-0.4，12.7） center(0.77,-0.4,0.0) upDirection(0,1,0) zfar = 19,redius = 6.3 return camera.release(); } int main( int argc, char** argv ) { osg::ArgumentParser arguments( &argc, argv ); osg::Node* model = osgDB::readNodeFiles( arguments ); if ( !model ) model = osgDB::readNodeFile( "cow.osg" ); osg::Camera* camera = createBirdsEye( model->getBound() ); camera->addChild( model ); osgViewer::Viewer viewer; viewer.setSceneData( camera ); viewer.setUpViewInWindow(40,40,800,600); return viewer.run(); }
代碼執行效果：
放開代碼中相應的注釋，可以看到下面的效果：
從前面看牛
從牛頭看牛：
從牛下巴看牛：
再加入一頭牛，使兩頭牛的坐標分別為(0.0,-10.0,0.0)、(0.0,-30.0,0.0),改用透視投影，視點的坐標為(0.0,-50.0,5)。代碼如下：
1 #include <osg/Camera> 2 #include <osgDB/ReadFile> 3 #include <osgViewer/Viewer> 4 #include <osg/PositionAttitudeTransform> 5 6 osg::Camera* createBirdsEye( const osg::BoundingSphere& bs ) 7 { 8 osg::ref_ptr<osg::Camera> camera = new osg::Camera; 9 camera->setClearMask( GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT ); 10 camera->setReferenceFrame( osg::Transform::ABSOLUTE_RF ); 11 12 double viewDistance = 2.0 * bs.radius(); 13 double znear = viewDistance - bs.radius(); 14 double zfar = viewDistance + bs.radius(); 15 float top = bs.radius(); 16 float right = bs.radius(); 17 float bottom = top; 18 float left = right; 19 //osg左手系坐標(z+向上，x+向右，y+向里) 20 21 //透視投影 22 camera->setProjectionMatrixAsFrustum( -left, right, -bottom, top, 18, 39.2 ); 23 24 osg::Vec3d upDirection( 0.0,1.0,0.0 ); 25 osg::Vec3d viewDirection( 0.0,0.0,1.0 ); 26 osg::Vec3d center = bs.center(); 27 osg::Vec3d eyePoint = center + viewDirection * viewDistance; 28 //從前面看牛（視點） 29 eyePoint.set(0.0,-50.0,5.0); 30 31 //camera->setComputeNearFarMode(osg::CullSettings::DO_NOT_COMPUTE_NEAR_FAR); 32 camera->setViewMatrixAsLookAt( eyePoint, center, upDirection );//相機位置（眼睛位置，眼睛看到的場景中心位置，視點向上的量） 33 // center(0.77,-0.4,0.0) upDirection(0,1,0) zfar = 19,redius = 6.3 34 35 return camera.release(); 36 } 37 38 int main( int argc, char** argv ) 39 { 40 osg::ArgumentParser arguments( &argc, argv ); 41 osg::Node* model = osgDB::readNodeFiles( arguments ); 42 if ( !model ) model = osgDB::readNodeFile( "cow.osg" ); 43 44 45 osg::Camera* camera = createBirdsEye( model->getBound() ); 46 47 //牛1 48 osg::ref_ptr<osg::PositionAttitudeTransform> pat = new osg::PositionAttitudeTransform; 49 pat->setPosition(osg::Vec3(0.0,-30.0,0.0)); 50 pat->addChild(model); 51 52 //牛2 53 osg::ref_ptr<osg::PositionAttitudeTransform> pat2 = new osg::PositionAttitudeTransform; 54 pat2->setPosition(osg::Vec3(0.0,-10.0,0.0)); 55 pat2->addChild(model); 56 57 58 59 camera->addChild(pat); 60 camera->addChild(pat2); 61 62 osgViewer::Viewer viewer; 63 viewer.setSceneData( camera ); 64 viewer.setUpViewInWindow(40,40,800,600); 65 return viewer.run(); 66 }
運行效果：
如果打開31行的注釋（如果不打開這個注釋，osg默認對near、far不做裁剪），其運行效果如下：
可以看到后邊的牛只顯示了半個，另外半個被裁剪掉了，圖解如下：
黃色區域為near、far所表示的裁剪區域，牛2被裁剪了。
（有五個窗口）單個視景器多個從相機看一頭牛：
上述效果實現代碼：
#include <osg/Group> #include <osgDB/ReadFile> #include <osgViewer/Viewer> #include <osg/PositionAttitudeTransform> //為相機設置圖形設備對象並返回相機 osg::Camera* createCamera( int x, int y, int w, int h ) { osg::ref_ptr<osg::GraphicsContext::Traits> traits = new osg::GraphicsContext::Traits; traits->windowDecoration = false;//是否設置標題欄，這里設定為否，有標題欄的話，中間會被標題難割開。 traits->x = x;//左上角坐標x traits->y = y;//左上角坐標y traits->width = w; traits->height = h; traits->doubleBuffer = true; osg::DisplaySettings* ds = osg::DisplaySettings::instance(); traits->alpha = ds->getMinimumNumAlphaBits(); traits->stencil = ds->getMinimumNumStencilBits(); //模板緩存 traits->sampleBuffers = ds->getMultiSamples();//重采樣緩存 traits->samples = ds->getNumMultiSamples();//重采樣數 //構建圖形設備對象 osg::ref_ptr<osg::GraphicsContext> gc =osg::GraphicsContext::createGraphicsContext( traits.get() ); osg::ref_ptr<osg::Camera> camera = new osg::Camera; camera->setGraphicsContext( gc.get() );//設置相機的圖形設備對象 camera->setViewport( new osg::Viewport(0,0, traits->width, traits->height) ); return camera.release(); } int main( int argc, char** argv ) { osg::ArgumentParser arguments( &argc, argv ); osg::Node* model = osgDB::readNodeFiles( arguments ); if ( !model ) model = osgDB::readNodeFile( "cow.osg" ); osgViewer::Viewer viewer; //不做投影偏移的牛 viewer.addSlave( createCamera(900,300,600,450), osg::Matrixd::translate( 0.0,0,0.0), osg::Matrixd() ); viewer.addSlave( createCamera(50,50,400,300), osg::Matrixd::translate( 1.0,-1.0,0.0), osg::Matrixd() ); viewer.addSlave( createCamera(455,50,400,300), osg::Matrixd::translate(-1.0,-1.0,0.0), osg::Matrixd() ); viewer.addSlave( createCamera(50,355,400,300), osg::Matrixd::translate( 1.0,1.0,0.0), osg::Matrixd() ); viewer.addSlave( createCamera(455,355,400,300), osg::Matrixd::translate(-1.0, 1.0,0.0), osg::Matrixd() ); viewer.setSceneData( model ); osg::Vec3d center = model ->getBound().center(); return viewer.run(); }
總結：一頭牛，添加了五個從相機去觀察，每個相機對應一個圖像設備窗口。
（有兩窗口）用多視景器多方位觀察一頭牛：
實現代碼：
#include <osg/Group> #include <osgDB/ReadFile> #include <osgViewer/CompositeViewer> #include <osg/PositionAttitudeTransform> //回調函數，讓其不斷的旋轉 class RotateCallback : public osg::NodeCallback { public: RotateCallback() : _rotateZ(0.0) {} virtual void operator()( osg::Node* node, osg::NodeVisitor* nv ) { osg::PositionAttitudeTransform* pat = dynamic_cast<osg::PositionAttitudeTransform*>( node ); if ( pat ) { osg::Quat quat( osg::DegreesToRadians(_rotateZ), osg::Z_AXIS ); pat->setAttitude( quat ); _rotateZ += 1.0; } traverse( node, nv );//訪問器的下一個節點 } protected: double _rotateZ; }; osg::Camera* createCamera( const osg::BoundingSphere& bs ) { osg::ref_ptr<osg::Camera> camera = new osg::Camera; camera->setClearMask( GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT ); camera->setReferenceFrame( osg::Transform::ABSOLUTE_RF ); double viewDistance = 2.0 * bs.radius(); double znear = viewDistance - bs.radius(); double zfar = viewDistance + bs.radius(); float top = bs.radius(); float right = bs.radius(); float bottom = top; float left = right; //osg左手系坐標(z+向上，x+向右，y+向里) //透視投影 camera->setProjectionMatrixAsFrustum( -left, right, -bottom, top, znear, zfar ); osg::Vec3d upDirection( 0.0,0.0,1.0 ); osg::Vec3d center = bs.center(); osg::Vec3d eyePoint ; eyePoint.set(0.0,0.0,10.0); camera->setComputeNearFarMode(osg::CullSettings::DO_NOT_COMPUTE_NEAR_FAR); camera->setViewMatrixAsLookAt( eyePoint, center, upDirection );//相機位置（眼睛位置，眼睛看到的場景中心位置，視點向上的量） return camera.release(); } int main( int argc, char** argv ) { //讀牛 osg::ArgumentParser arguments( &argc, argv ); osg::Node* model = osgDB::readNodeFiles( arguments ); if ( !model ) model = osgDB::readNodeFile( "cow.osg" ); //創建投影相機 osg::Camera* camera = createCamera( model->getBound() ); //給牛模型設置回調，讓其自動旋轉 osg::ref_ptr<osg::PositionAttitudeTransform> pat = new osg::PositionAttitudeTransform; pat->addChild( model ); pat->setUpdateCallback( new RotateCallback ); camera->addChild(pat.get()); //視景器1顯示第一個有設置特定相機的牛 osg::ref_ptr<osgViewer::View> view1 = new osgViewer::View; view1->setUpViewInWindow( 0, 50, 320, 240 ); view1->setSceneData( camera ); //視景器2顯示第二個默認相機的牛 osg::ref_ptr<osgViewer::View> view2 = new osgViewer::View; view2->setUpViewInWindow( 340, 50, 320, 240 ); view2->setSceneData( pat.get() ); //多視景器進行管理並渲染 osgViewer::CompositeViewer compositeViewer; compositeViewer.addView( view1.get() ); compositeViewer.addView( view2.get() ); return compositeViewer.run(); }
總結：一個圖像設備，多視景器管理着兩個視景器，每個視景器對應一個相機（camera本身也是一個矩陣）。
單窗口顯示兩頭牛：
實現代碼：
#include <osg/Group> #include <osgDB/ReadFile> #include <osgViewer/Viewer> #include <osg/PositionAttitudeTransform> #include <osgViewer/CompositeViewer> int main( int argc, char** argv ) { osg::ArgumentParser arguments( &argc, argv ); osg::Node* model = osgDB::readNodeFiles( arguments ); if ( !model ) model = osgDB::readNodeFile( "cow.osg" ); osg::ref_ptr<osg::GraphicsContext::Traits> traits = new osg::GraphicsContext::Traits; traits->windowDecoration = false;//是否設置標題欄，這里設定為否，有標題欄的話，中間會被標題難割開。 traits->x = 0;//左上角坐標x traits->y = 0;//左上角坐標y traits->width = 800; traits->height = 800; traits->doubleBuffer = true; osg::DisplaySettings* ds = osg::DisplaySettings::instance(); traits->alpha = ds->getMinimumNumAlphaBits(); traits->stencil = ds->getMinimumNumStencilBits(); //模板緩存 traits->sampleBuffers = ds->getMultiSamples();//重采樣緩存 traits->samples = ds->getNumMultiSamples();//重采樣數 //構建圖形設備對象 osg::ref_ptr<osg::GraphicsContext> gc =osg::GraphicsContext::createGraphicsContext( traits.get() ); osgViewer::CompositeViewer *v = new osgViewer::CompositeViewer(); osg::ref_ptr<osg::Group> g = new osg::Group; osg::ref_ptr<osg::Group> g2 = new osg::Group; osgViewer::View *v1 = new osgViewer::View(); osgViewer::View *v2 = new osgViewer::View(); v->addView(v1); v->addView(v2); v1->setSceneData(model); v2->setSceneData(model); v1->getCamera()->setViewport(new osg::Viewport(0,0,400,600)); v1->getCamera()->setGraphicsContext(gc.get()); v2->getCamera()->setViewport(new osg::Viewport(410,0,400,600)); v2->getCamera()->setGraphicsContext(gc.get()); return v->run(); }