【ARTOOlkit】openGL的glVertex()函数的用法
本篇文章算是对OpenGL内容的一些补充，这章内容是教会大家如何在模型外面用函数构建其他模型，继上篇文章的一个小发现，上篇内容是发现一个标识可以通过函数构建多个模型。
这次我们利用OpenGL中的模式GL_LINE_LOOP和模式GL_LINES来在茶壶模型外面画一个长方体。OpenGL中定义的定点放在函数glBegin和glEnd之间，由函数glBegin 的参数指定绘制图元的类型。
在glBegin()和glEnd()之间可调用的函数
函数 函数意义
glVertex*() 设置顶点坐标
glColor*() 设置当前颜色
glIndex*() 设置当前颜色表
glNormal*() 设置法向坐标
glEvalCoord*() 产生坐标
glCallList(),glCallLists() 执行显示列表
glTexCoord*() 设置纹理坐标
glEdgeFlag*() 控制边界绘制
glMaterial*() 设置材质
首先，我们给大家介绍一下这两个函数，这两个函数是glBegin 可支持的OpenGL图元
GL_LINES： 将指定的顶点用于创建线段。每两个顶点指定一条单独的线段。如果顶点的个数是奇数，则忽略最后一个。
GL_LINE_LOOP ： 特性和GL_LINE_STRIP相似，只不过最后一条线段是在指定的最后一个和第一个顶点之间绘制。典型情况下，这用于绘制哪些可能违反了GL_POLYGON用法规则的封闭区域。
表示方法：
glBegin(GL_LINE_LOOP);
glVertex3f( 90.0f, 60.0f, 0.0f );
glVertex3f( 90.0f, 60.0f, 0.0f );
glEnd();
glVertex3f(x, y, z),这个函数是在空间中确定点的函数。我们这里X,Y,Z的值都是通过标识卡的坐标系来确定的。如下图所示，。
我们用这个函数在茶壶模型外面构建了长方体，并把他写到我们自己写的static void drawCuboid()函数中，然后在draw（）函数里面执行，具体代码如下，我们的代码是在simple2的基础上添加了代码，添加的部分我用红色标记。
#ifdef _WIN32
#include
#endif
#include
#include
#ifndef __APPLE__
#include
#include
#else
#include
#include
#endif
#include
#include
#include
#include
/* set up the video format globals */
#ifdef _WIN32
char *vconf = "Data\\WDM_camera_flipV.xml";
#else
char *vconf = "";
#endif
int xsize, ysize;
int thresh = 100;
int count = 0;
int mode = 1;//标识位
char *cparam_name = "Data/camera_para.dat";
ARParam cparam;
char *patt_name = "Data/patt.hiro";
int patt_id;
int patt_width = 80.0;
double patt_center[2] = {0.0, 0.0};
double patt_trans[3][4];
static void init(void);
static void cleanup(void);
static void keyEvent( unsigned char key, int x, int y);
static void mainLoop(void);
static void draw( double trans[3][4] );
int main(int argc, char **argv)
{
glutInit(&argc, argv);
init();
arVideoCapStart();
argMainLoop( NULL, keyEvent, mainLoop );
return (0);
}
static void keyEvent( unsigned char key, int x, int y)
{
/* quit if the ESC key is pressed */
if( key == 0x1b ) {
printf("*** %f (frame/sec)\n", (double)count/arUtilTimer());
cleanup();
exit(0);
}
//如果键盘输入c
if( key == 'c' ) {
printf("*** %f (frame/sec)\n", (double)count/arUtilTimer());
count = 0;
mode = 1 - mode;//让每次键盘输入c都让mode变化
//此处mode转换为布尔型，如果mode=0，则为假arGetTransMatCont
if( mode ) printf("Continuous mode: Using arGetTransMatCont.\n");
//如果mode不为假，输出arGetTransMat
else printf("One shot mode: Using arGetTransMat.\n");
}
}
/* main loop */
static void mainLoop(void)
{
static int contF = 0;//静态变量
ARUint8 *dataPtr;
ARMarkerInfo *marker_info;
int marker_num;
int j, k;
/* grab a vide frame */
if( (dataPtr = (ARUint8 *)arVideoGetImage()) == NULL ) {
arUtilSleep(2);
return;
}
if( count == 0 ) arUtilTimerReset();
count++;
argDrawMode2D();
argDispImage( dataPtr, 0,0 );
/* detect the markers in the video frame */
if( arDetectMarker(dataPtr, thresh, &marker_info, &marker_num) < 0 ) {
cleanup();
exit(0);
}
arVideoCapNext();
/* check for object visibility */
k = -1;
for( j = 0; j < marker_num; j++ ) {
if( patt_id == marker_info[j].id ) {
if( k == -1 ) k = j;
else if( marker_info[k].cf < marker_info[j].cf ) k = j;
}
}
if( k == -1 ) {
contF = 0;
argSwapBuffers();
return;
}
/*计算摄像头的转移矩阵，标识卡和摄像机之间的转移信息通过使用函数*/
//mode为0
if( mode == 0 || contF == 0 ) {
arGetTransMat(&marker_info[k], patt_center, patt_width, patt_trans);
}
else {
//mode为1
arGetTransMatCont(&marker_info[k], patt_trans, patt_center, patt_width, patt_trans);
}
contF = 1;
draw( patt_trans );
argSwapBuffers();
}
static void init( void )
{
ARParam wparam;
/* open the video path */
if( arVideoOpen( vconf ) < 0 ) exit(0);
/* find the size of the window */
if( arVideoInqSize(&xsize, &ysize) < 0 ) exit(0);
printf("Image size (x,y) = (%d,%d)\n", xsize, ysize);
/* set the initial camera parameters */
if( arParamLoad(cparam_name, 1, &wparam) < 0 ) {
printf("Camera parameter load error !!\n");
exit(0);
}
arParamChangeSize( &wparam, xsize, ysize, &cparam );
arInitCparam( &cparam );
printf("*** Camera Parameter ***\n");
arParamDisp( &cparam );
if( (patt_id=arLoadPatt(patt_name)) < 0 ) {
printf("pattern load error !!\n");
exit(0);
}
/* open the graphics window */
argInit( &cparam, 1.0, 0, 0, 0, 0 );
}
/* cleanup function called when program exits */
static void cleanup(void)
{
arVideoCapStop();
arVideoClose();
argCleanup();
}
//利用GL_LINE_LOOP和GL_LINES画长方体，在茶壶外面画长方体
static void drawCuboid()//画长方体
{
glBegin(GL_LINE_LOOP);
glVertex3f( 90.0f, 60.0f, 0.0f );
glVertex3f( -90.0f, 60.0f, 0.0f );
glVertex3f( -90.0f, 60.f, 50.0f );
glVertex3f( 90.0f, 60.0f, 50.0f );
glVertex3f( 90.0f, -60.0f,50.0f );
glVertex3f( -90.0f, -60.0f, 50.0f );
glVertex3f( -90.0f, -60.f, 0.0f );
glVertex3f( 90.0f, -60.0f, 0.0f );
glVertex3f( 90.0f, 40.0f, 0.0f );
glVertex3f( -90.0f, 40.0f, 0.0f );
glVertex3f( -90.0f, 40.0f, 50.0f );
glVertex3f( 90.0f, 40.0f, 50.0f );
glVertex3f( 90.0f, -40.0f, 50.0f );
glVertex3f( -90.0f, -40.0f, 50.0f );
glVertex3f( -90.0f, -40.0f, 0.0f );
glVertex3f( 90.0f, -40.0f, 0.0f );
glVertex3f( 90.0f, 20.0f, 0.0f );
glVertex3f( -90.0f, 20.0f, 0.0f );
glVertex3f( -90.0f, 20.0f, 50.0f );
glVertex3f( 90.0f, 20.0f, 50.0f );
glVertex3f( 90.0f, -20.0f, 50.0f );
glVertex3f( -90.0f, -20.0f, 50.0f );
glVertex3f( -90.0f, -20.0f, 0.0f );
glVertex3f( 90.0f, -20.0f, 0.0f );
glVertex3f( 90.0f, 0.0f, 0.0f );
glVertex3f( -90.0f, 0.0f, 0.0f );
glVertex3f( -90.0f, 0.0f, 50.0f );
glVertex3f( 90.0f, 0.0f, 50.0f );
glVertex3f( 90.0f, -0.0f, 50.0f );
glVertex3f( -90.0f, -0.0f, 50.0f );
glVertex3f( -90.0f, -0.0f, 0.0f );
glVertex3f( 90.0f, -0.0f, 0.0f );
glEnd();
glBegin(GL_LINES);
glVertex3f( 90.0f, -60.0f, 0.0f );
glVertex3f( 90.0f,-60.0f, 50.0f );
glVertex3f( -90.0f, -60.0f,0.0f );
glVertex3f( -90.0f, 60.0f, 0.0f );
glVertex3f( -90.0f, -60.f, 50.0f );
glVertex3f( -90.0f, 60.0f, 50.0f );
glVertex3f( 90.0f, 60.0f, 0.0f );
glVertex3f( 90.0f, 60.0f, 50.0f );
glVertex3f( 90.0f, -40.0f, 0.0f );
glVertex3f( 90.0f, -40.0f, 50.0f );
glVertex3f( 90.0f, 40.0f, 0.0f );
glVertex3f( 90.0f, 40.0f, 50.0f );
glVertex3f( 90.0f, -20.0f, 0.0f );
glVertex3f( 90.0f, -20.0f, 50.0f );
glVertex3f( 90.0f, 20.0f, 0.0f );
glVertex3f( 90.0f, 20.0f, 50.0f );
glVertex3f( 90.0f, 0.0f, 0.0f );
glVertex3f( 90.0f, 0.0f, 50.0f );
glEnd();
}
static void draw( double trans[3][4] )
{
double gl_para[16];
GLfloat mat_ambient[] = {0.0, 0.0, 1.0, 1.0};
GLfloat mat_flash[] = {0.0, 0.0, 1.0, 1.0};
GLfloat mat_flash_shiny[] = {50.0};
GLfloat light_position[] = {100.0,-200.0,200.0,0.0};
GLfloat ambi[] = {0.1, 0.1, 0.1, 0.1};
GLfloat lightZeroColor[] = {0.9, 0.9, 0.9, 0.1};
argDrawMode3D();
argDraw3dCamera( 0, 0 );
glClearDepth( 1.0 );
glClear(GL_DEPTH_BUFFER_BIT);
glEnable(GL_DEPTH_TEST);
glDepthFunc(GL_LEQUAL);
/* load the camera transformation matrix */
argConvGlpara(trans, gl_para);
glMatrixMode(GL_MODELVIEW);
glLoadMatrixd( gl_para );
glEnable(GL_LIGHTING);
glEnable(GL_LIGHT0);
glLightfv(GL_LIGHT0, GL_POSITION, light_position);
glLightfv(GL_LIGHT0, GL_AMBIENT, ambi);
glLightfv(GL_LIGHT0, GL_DIFFUSE, lightZeroColor);
glMaterialfv(GL_FRONT, GL_SPECULAR, mat_flash);
glMaterialfv(GL_FRONT, GL_SHININESS, mat_flash_shiny);
glMaterialfv(GL_FRONT, GL_AMBIENT, mat_ambient);
glMatrixMode(GL_MODELVIEW);
glRotatef(90,1,0,0);//旋转函数，如果不旋转，茶壶的底座就不在标识卡上
glTranslatef( 25.0, 25.0, 10.0 );//平移函数
glutSolidTeapot(50.0);//茶壶函数
drawCuboid();//画长方体
glLineWidth(10.0);//设置线宽
glDisable( GL_LIGHTING );
glDisable( GL_DEPTH_TEST );
}
结果显示如下
其中我还添加了一个可以改变构建的长方体的线宽，glLineWidth就是这个函数。
这篇文章教了我们OpenGL中的知识，不仅可以考给出的函数模型来显示在标识卡上，也可以自己画出模型，其中用 glVertex3f（）函数时，需要确定函数里面的参数，也就是x,y,z的值，这个需要自己确定出自己已有模型的位置，才好输入到 glVertex3f函数的参数中，这个我认为是比较难确定的部分。这里面x,y,z的值都是通过标识卡的坐标系来决定的。我们要分清，什么时候是摄像机的坐标系，什么时候是标识卡的坐标系。