OpenGL--模板测试

• 理论基础
  模板测试：通俗点讲就是为屏幕每个像素设置了一个模板值，然后拿一个参考值与之比较，满足条件就通过，则对应像素就会绘制，否则不绘制。类似深度测试一样，只是服务情形不同，深度测试主要用来消除背面的，而模板测试主要可以实现裁剪，指明哪里可以绘制，哪里不绘制。(比较规则:glStencilFunc，修改模板缓冲区的值:glStencilOp)

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• 代码示例

1，模板实现裁剪实例

#include "GLTools.h"#ifdef __APPLE__#include <glut/glut.h>#else#define FREEGLUT_STATIC#include <GL/glut.h>#endif#define YELLOWMAT   1#define BLUEMAT 2void init (void){    GLfloat yellow_diffuse[] = { 0.7, 0.7, 0.0, 1.0 };    GLfloat yellow_specular[] = { 1.0, 1.0, 1.0, 1.0 };    GLfloat blue_diffuse[] = { 0.1, 0.1, 0.7, 1.0 };    GLfloat blue_specular[] = { 0.1, 1.0, 1.0, 1.0 };    GLfloat position_one[] = { 1.0, 1.0, 1.0, 0.0 };    glNewList(YELLOWMAT, GL_COMPILE);    glMaterialfv(GL_FRONT, GL_DIFFUSE, yellow_diffuse);    glMaterialfv(GL_FRONT, GL_SPECULAR, yellow_specular);    glMaterialf(GL_FRONT, GL_SHININESS, 64.0);    glEndList();    glNewList(BLUEMAT, GL_COMPILE);    glMaterialfv(GL_FRONT, GL_DIFFUSE, blue_diffuse);    glMaterialfv(GL_FRONT, GL_SPECULAR, blue_specular);    glMaterialf(GL_FRONT, GL_SHININESS, 45.0);    glEndList();    glLightfv(GL_LIGHT0, GL_POSITION, position_one);    glEnable(GL_LIGHT0);    glEnable(GL_LIGHTING);    glEnable(GL_DEPTH_TEST);    glClearStencil(0x0);//设置以 0 来重置模板缓冲区的值    glEnable(GL_STENCIL_TEST);//激活模板测试}void display(void){    glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);    /* 绘制圆 */    /*模板控制的像素筛选方式*/    glStencilFunc (GL_EQUAL, 0x1, 0x1);//模板缓冲区值=1对应的像素才绘制    /*模板缓冲区中的值修改方式(3个参数对应3种情况下的操作：1，模板测试失败 2，模板测试通过，深度测试失败 3，模板深度测试都通过)*/    glStencilOp (GL_KEEP, GL_KEEP, GL_KEEP);//模板缓冲区的值保存不变    glCallList (BLUEMAT);    glutSolidSphere (0.5, 15, 15);    /* 绘制两个圆环 */    glStencilFunc (GL_NOTEQUAL, 0x1, 0x1);//不等于1才绘制    glPushMatrix();    glRotatef (45.0, 0.0, 0.0, 1.0);    glRotatef (45.0, 0.0, 1.0, 0.0);    glCallList (YELLOWMAT);    glutSolidTorus (0.275, 0.85, 15, 15);    glPushMatrix();    glRotatef (90.0, 1.0, 0.0, 0.0);    glutSolidTorus (0.275, 0.85, 15, 15);    glPopMatrix();    glPopMatrix();    glFlush();}void reshape(int w, int h){    glViewport(0, 0, (GLsizei) w, (GLsizei) h);    glMatrixMode(GL_PROJECTION);    glLoadIdentity();    if (w <= h)        gluOrtho2D(-3.0, 3.0, -3.0*(GLfloat)h/(GLfloat)w,                   3.0*(GLfloat)h/(GLfloat)w);    else        gluOrtho2D(-3.0*(GLfloat)w/(GLfloat)h,                   3.0*(GLfloat)w/(GLfloat)h, -3.0, 3.0);    glMatrixMode(GL_MODELVIEW);    glLoadIdentity();    glClear(GL_STENCIL_BUFFER_BIT);//清除模板缓冲区    glStencilFunc (GL_ALWAYS, 0x1, 0x1);//总是通过    glStencilOp (GL_REPLACE, GL_REPLACE, GL_REPLACE);//用上面设置的参考值0x1替换模板缓冲区的值    glBegin(GL_QUADS);//绘制方形    glVertex2f (-1.0, 0.0);    glVertex2f (0.0, 1.0);    glVertex2f (1.0, 0.0);    glVertex2f (0.0, -1.0);    glEnd();    glMatrixMode(GL_PROJECTION);    glLoadIdentity();    gluPerspective(45.0, (GLfloat) w/(GLfloat) h, 3.0, 7.0);    glMatrixMode(GL_MODELVIEW);    glLoadIdentity();    glTranslatef(0.0, 0.0, -5.0);}void keyboard(unsigned char key, int x, int y){    switch (key) {        case 27:            exit(0);            break;    }}int main(int argc, char** argv){    glutInit(&argc, argv);    glutInitDisplayMode (GLUT_SINGLE | GLUT_RGB                         | GLUT_DEPTH | GLUT_STENCIL);    glutInitWindowSize (400, 400);    glutInitWindowPosition (100, 100);    glutCreateWindow (argv[0]);    init ();    glutReshapeFunc(reshape);    glutDisplayFunc(display);    glutKeyboardFunc(keyboard);    glutMainLoop();    return 0;}

2，平面镜反射实例

#include "GLTools.h"#ifdef __APPLE__#include <glut/glut.h>#else#define FREEGLUT_STATIC#include <GL/glut.h>#endifvoid drawSphere(){    // 设置光源    glEnable(GL_LIGHTING);    glEnable(GL_LIGHT0);    {        GLfloat        pos[]      = {5.0f, 5.0f, 0.0f, 1.0f},        ambient[] = {0.0f, 0.0f, 1.0f, 1.0f};        glLightfv(GL_LIGHT0, GL_POSITION, pos);        glLightfv(GL_LIGHT0, GL_AMBIENT, ambient);    }    // 绘制一个球体    glColor3f(1, 0, 0);    glPushMatrix();    glTranslatef(0, 0, 2);    glutSolidSphere(0.5, 20, 20);    glPopMatrix();}void display(void){    // 清除屏幕    glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);    glEnable(GL_DEPTH_TEST);    // 绘制前面球体    glDisable(GL_STENCIL_TEST);    drawSphere();    // 绘制一个平面镜。    // 为了保证平面镜之后的镜像能够正确绘制，在绘制平面镜时需要将深度缓冲区设置为只读的。    // 在绘制时暂时关闭光照效果    glClearStencil(0);    glClear(GL_STENCIL_BUFFER_BIT);    glStencilFunc(GL_ALWAYS, 1, 0xFF);    glStencilOp(GL_KEEP, GL_KEEP, GL_REPLACE);    glEnable(GL_STENCIL_TEST);    glDisable(GL_LIGHTING);    glColor3f(0.5f, 0.5f, 0.5f);    glDepthMask(GL_FALSE);//深度缓冲区不能写入(只读)    glRectf(-1.5f, -1.5f, 1.5f, 1.5f);//即这个绘制不会覆盖以前像素，而是丢弃自己    glDepthMask(GL_TRUE);//恢复写入    // 绘制一个与先前球体关于平面镜对称的球体，注意光源的位置也要发生对称改变    // 因为平面镜是在X轴和Y轴所确定的平面，所以只要Z坐标取反即可实现对称    // 为了保证球体的绘制范围被限制在平面镜内部，使用模板测试    glStencilFunc(GL_EQUAL, 1, 0xFF);    glStencilOp(GL_KEEP, GL_KEEP, GL_REPLACE);    glScalef(1.0f, 1.0f, -1.0f);    drawSphere();    glFlush();}void reshape(int w, int h){    if(h == 0)        h = 1;    glViewport(0, 0, (GLsizei) w, (GLsizei) h);    glMatrixMode(GL_PROJECTION);    glLoadIdentity();    gluPerspective(60, (GLfloat) w/(GLfloat) h, 5, 25);    glMatrixMode(GL_MODELVIEW);    glLoadIdentity();    gluLookAt(5, 0, 6.5, 0, 0, 0, 0, 1, 0);}void keyboard(unsigned char key, int x, int y){    switch (key) {        case 27:            exit(0);            break;    }}int main(int argc, char** argv){    glutInit(&argc, argv);    glutInitDisplayMode (GLUT_SINGLE | GLUT_RGB                         | GLUT_DEPTH | GLUT_STENCIL);    glutInitWindowSize (400, 400);    glutInitWindowPosition (100, 100);    glutCreateWindow (argv[0]);    glutReshapeFunc(reshape);    glutDisplayFunc(display);    glutKeyboardFunc(keyboard);    glutMainLoop();    return 0;}