用OpenInventor实现的NeHe OpenGL教程－第二十五课_openinvertor如何在场景中画线条-优快云博客

本文链接：https://blog.youkuaiyun.com/RobinHao/article/details/2229537

本文介绍如何使用OpenInventor实现3D模型从一种形态平滑过渡到另一种形态的技术。通过加载不同的3D模型并计算顶点变化，实现动态变换效果。

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用OpenInventor实现的NeHe OpenGL教程－第二十五课

NeHe教程在这节课中向我们介绍了如何从文件加载3D模型，并且平滑的从一个模型变换为另一个模型。两个模型之间平滑过渡的算法其实是很简单的，首先我们要保证两个模型要有相同数目的顶点，然后我们分别计算每个点从一个模型移动到另外一个模型时，中间的位置数据。我们将这个过程显示出来就会产生模型平滑过渡的效果。

因为我们的程序采用NeHe提供的3D模型数据，所以我们就直接使用NeHe的代码来读取3D模型数据的代码。本节课程采用的技术都是前面的课程已经介绍过的。我们就不再详细介绍了。

下面的代码都是拷贝自NeHe教程，主要是用来读取3D模型数据，具体的解释请查阅NeHe教程。

typedef struct // Structure For 3D Points

{

float x, y, z; // X, Y & Z Points

} VERTEX; // Called VERTEX

typedef struct // Structure For An Object

{

int verts; // Number Of Vertices For The Object

VERTEX *points; // One Vertice (Vertex x,y & z)

} OBJECT; // Called OBJECT

int key = 1;

int maxver; // Will Eventually Hold The Maximum Number Of Vertices

OBJECT morph1,morph2,morph3,morph4,// Our 4 Morphable Objects (morph1,2,3 & 4)

helper,*sour,*dest;// Helper Object, Source Object, Destination Object

float xrot = 0,yrot = 0,zrot = 0, // X, Y & Z Rotation

xspeed = 0,yspeed = 0,zspeed = 0,// X, Y & Z Spin Speed

cx = 0,cy = 0,cz = -15; // X, Y & Z Position

int step = 0,steps = 100; // Step Counter And Maximum Number Of Steps

bool morph = FALSE; // Default morph To False (Not Morphing)

void objallocate(OBJECT *k,int n) // Allocate Memory For Each Object

{

// And Defines points

k->points = (VERTEX*)malloc(sizeof(VERTEX) * n);

}

// (3 Points For Each Vertice)

void objfree(OBJECT *k) // Frees The Object (Releasing The Memory)

{

free(k->points); // Frees Points

}

void readstr(FILE *f,char *string) // Reads A String From File (f)

{

fgets(string, 255, f); // Gets A String Of 255 Chars Max From f (File)

} while ((string[0] == '/') || (string[0] == '/n'));// Until End Of Line Is Reached

}

void objload(char *name,OBJECT *k) // Loads Object From File (name)

{

int ver; // Will Hold Vertice Count

float rx,ry,rz; // Hold Vertex X, Y & Z Position

FILE *filein; // Filename To Open

char oneline[255]; // Holds One Line Of Text (255 Chars Max)

filein = fopen(name, "rt"); // Opens The File For Reading Text In Translated Mode

// CTRL Z Symbolizes End Of File In Translated Mode

readstr(filein,oneline); // Jumps To Code That Reads One Line Of Text From The File

sscanf(oneline, "Vertices: %d/n", &ver);

k->verts = ver; // Sets Objects verts Variable To Equal The Value Of ver

objallocate(k,ver); // Jumps To Code That Allocates Ram To Hold The Object

for (int i = 0;i < ver;i++) // Loops Through The Vertices

{

readstr(filein,oneline); // Reads In The Next Line Of Text

sscanf(oneline, "%f %f %f", &rx, &ry, &rz);

k->points[i].x = rx; // Sets Objects (k) points.x Value To rx

k->points[i].y = ry; // Sets Objects (k) points.y Value To ry

k->points[i].z = rz; // Sets Objects (k) points.z Value To rz

}

fclose(filein); // Close The File

if(ver>maxver)

maxver = ver; // If ver Is Greater Than maxver Set maxver Equal To ver

} // Keeps Track Of Highest Number Of Vertices Used In Any Of The

//这个函数是关键，用来计算平滑移动时，中间位置数据。

VERTEX calculate(int i) // Calculates Movement Of Points During Morphing

{

VERTEX a; // Temporary Vertex Called a

// a.x Value Equals Source x - Destination x Divided By Steps

a.x = (sour->points[i].x - dest->points[i].x) / steps;

// a.y Value Equals Source y - Destination y Divided By Steps

a.y = (sour->points[i].y - dest->points[i].y) / steps;

// a.z Value Equals Source z - Destination z Divided By Steps

a.z = (sour->points[i].z - dest->points[i].z) / steps;

return a;

}

我们将在函数BuildScene中创建场景数据。

void BuildScene(void)

{

//定义事件回调节点，用来响应键盘消息

SoEventCallback* pEventCallback = new SoEventCallback;

pEventCallback->addEventCallback(SoKeyboardEvent::getClassTypeId(),

KeyboardEventCB,

g_pOivSceneRoot);

g_pOivSceneRoot->addChild(pEventCallback);

//读取3D模型数据，初始化顶点信息

maxver = 0; // Sets Max Vertices To 0 By Default

objload("../data/sphere.txt",&morph1);

objload("../data/torus.txt",&morph2);

objload("../data/tube.txt",&morph3);

objallocate(&morph4,486); // Manually Reserver Ram For A 4th 468 Vertice Object (morph4)

for(int i = 0;i < 486;i++) // Loop Through All 468 Vertices

{

// morph4 x Point Becomes A Random Float Value From -7 to 7

morph4.points[i].x = ((float)(rand()%14000) / 1000) - 7;

// morph4 y Point Becomes A Random Float Value From -7 to 7

morph4.points[i].y = ((float)(rand()%14000) / 1000) - 7;

// morph4 z Point Becomes A Random Float Value From -7 to 7

morph4.points[i].z = ((float)(rand()%14000) / 1000) - 7;

}

// Load sphere.txt Object Into Helper (Used As Starting Point)

objload("../data/sphere.txt",&helper);

sour = dest = &morph1; // Source & Destination Are Set To Equal First Object (morph1)

//构造位置节点

g_pPosTrans = new SoTranslation;

g_pOivSceneRoot->addChild(g_pPosTrans);

g_pPosTrans->translation.setValue(cx,cy,cz);

g_pXRotation = new SoRotation;

g_pOivSceneRoot->addChild(g_pXRotation);

g_pXRotation->rotation.setValue(SbVec 3f (1,0,0),xrot);

g_pYRotation = new SoRotation;

g_pOivSceneRoot->addChild(g_pYRotation);

g_pYRotation->rotation.setValue(SbVec 3f (0,1,0),yrot);

g_pZRotation = new SoRotation;

g_pOivSceneRoot->addChild(g_pZRotation);

g_pZRotation->rotation.setValue(SbVec 3f (0,0,1),zrot);

g_pPointColor = new SoBaseColor;

g_pOivSceneRoot->addChild(g_pPointColor);

g_pPointColor->rgb.setValue(0,0,1);

g_pPointCoord = new SoCoordinate3;

g_pOivSceneRoot->addChild(g_pPointCoord);

g_pPointCoord->point.setValuesPointer(helper.verts,(float *)helper.points);

SoPointSet *pPointSet = new SoPointSet;

pPointSet->numPoints = helper.verts;

g_pOivSceneRoot->addChild(pPointSet);

SoTimerSensor * texttimer = new SoTimerSensor(TimerSensorCB, NULL);

texttimer->setInterval(0.001);

texttimer->schedule();

}

下面的函数是定时时间回调函数，我们在这个函数中进行过渡计算。

void TimerSensorCB(void * data, SoSensor *)

{

if(morph && step <= steps)

{

VERTEX q; // Holds Returned Calculated Values For One Vertex

step++;

for(int i = 0;i < helper.verts; i++)

{ // The Same Amount Of Verts For Simplicity, Could Use maxver Also)

q = calculate(i); //这里开始计算中间位置

helper.points[i].x -= q.x;

helper.points[i].y -= q.y;

helper.points[i].z -= q.z;

g_pPointCoord->point.setValuesPointer(helper.verts,

(float *)helper.points);

}

else

{

if(step != 0)

g_pPointColor->rgb.setValue(0,0,1);

morph = FALSE;

sour = dest;

step = 0;

}

if(xspeed != 0)

{

xrot += xspeed;

g_pXRotation->rotation.setValue(SbVec 3f (1,0,0),xrot);

}

if(yspeed != 0)

{

yrot += yspeed;

g_pYRotation->rotation.setValue(SbVec 3f (0,1,0),yrot);

}

if(zspeed != 0)

{

zrot += zspeed;

g_pZRotation->rotation.setValue(SbVec 3f (0,0,1),zrot);

}

现在编译运行我们程序，屏幕会显示出一个由点组成的球体。按下2键，图形变形到圆环体，按下3键，图形变形到圆柱体，按下4键，图形变成空间随机离散点。按下1键，图形重新变回球体。按下上下左右箭头可以旋转物体。PageDown/PageUP放大缩小物体。W/S/A/D键用来平移物体。效果和NeHe第二十五是相同的。

本课的完整代码下载。（VC 2003 ＋ Coin2.5）

后记

OpenInventor是一种基于OpenGL的面向对象的三维图形软件开发包。使用这个开发包，程序员可以快速、简洁地开发出各种类型的交互式三维图形软件。这里不对OpenInventor做详细的介绍，读者如果感兴趣，可以阅读我的blog中的这篇文章《OpenInventor 简介》。

NeHe教程是目前针对初学者来说最好的OpenGL教程，它可以带领读者由浅入深，循序渐进地掌握OpenGL编程技巧。到目前为止（2007年11月），NeHe教程一共有48节。我的计划是使用OpenInventor来实现所有48节课程同样的效果。目的是复习和巩固OpenGL的知识，同时与各位读者交流OpenInventor的使用技巧。

因为篇幅的限制，我不会介绍NeHe教程中OpenGL的实现过程，因为NeHe的教程已经讲解的很清楚了，目前网络中也有NeHe的中文版本。我将使用VC 2003作为主要的编译器。程序框架采用和NeHe一样的Win32程序框架，不使用MFC。程序也可以在VC Express，VC 2005/2008中编译。我采用的OpenInventor开发环境是Coin，这是一个免费开源的OpenInventor开发库。文章《OpenInventor－Coin3D开发环境》介绍了如何在VC中使用Coin。我使用的Coin版本是2.5。读者可以到 www.coin3d.org 中免费下载。