如何在OpenGL中使用triangle_strip创建圆柱体纹理

对于中心：将i除以2 * PI，得到一个在0.0和1.0之间变化的数字，并将其用作纹理坐标：

for (i = 0; i <= 2 * PI; i += resolution)
{
    const float tc = ( i / (float)( 2 * PI ) );
    glTexCoord2f( tc, 0.0 );
    glVertex3f(radius * cos(i), 0, radius * sin(i));
    glTexCoord2f( tc, 1.0 );
    glVertex3f(radius * cos(i), height, radius * sin(i));
}
/* close the loop back to zero degrees */
glTexCoord2f( 0.0, 0.0 );
glVertex3f(radius, 0, 0);
glTexCoord2f( 0.0, 1.0 );
glVertex3f(radius, height, 0);

对于端盖：您可以（几乎）直接使用sin()/cos()输出：

glTexCoord2f( 0.5, 0.5 );
glVertex3f(0, height, 0);  /* center */
for (i = 0; i <= 2 * PI; i += resolution)
{
    // scale sin/cos range (-1 to 1) by 0.5 to get -0.5 to 0.5
    // then shift that range up/right by 0.5 to get 0 to 1:
    glTexCoord2f( 0.5f * cos(i) + 0.5f, 0.5f * sin(i) + 0.5f );
    glVertex3f(radius * cos(i), height, radius * sin(i));
}

完整示例：

#include <GL/glew.h>
#include <GL/glut.h>
#include <cmath>
void cylinder()
{
    const double PI = 3.14159;
    /* top triangle */
    double i, resolution  = 0.1;
    double height = 1;
    double radius = 0.5;
    glPushMatrix();
    glTranslatef(0, -0.5, 0);
    glBegin(GL_TRIANGLE_FAN);
        glTexCoord2f( 0.5, 0.5 );
        glVertex3f(0, height, 0);  /* center */
        for (i = 2 * PI; i >= 0; i -= resolution)
        {
            glTexCoord2f( 0.5f * cos(i) + 0.5f, 0.5f * sin(i) + 0.5f );
            glVertex3f(radius * cos(i), height, radius * sin(i));
        }
        /* close the loop back to 0 degrees */
        glTexCoord2f( 0.5, 0.5 );
        glVertex3f(radius, height, 0);
    glEnd();
    /* bottom triangle: note: for is in reverse order */
    glBegin(GL_TRIANGLE_FAN);
        glTexCoord2f( 0.5, 0.5 );
        glVertex3f(0, 0, 0);  /* center */
        for (i = 0; i <= 2 * PI; i += resolution)
        {
            glTexCoord2f( 0.5f * cos(i) + 0.5f, 0.5f * sin(i) + 0.5f );
            glVertex3f(radius * cos(i), 0, radius * sin(i));
        }
    glEnd();
    /* middle tube */
    glBegin(GL_QUAD_STRIP);
        for (i = 0; i <= 2 * PI; i += resolution)
        {
            const float tc = ( i / (float)( 2 * PI ) );
            glTexCoord2f( tc, 0.0 );
            glVertex3f(radius * cos(i), 0, radius * sin(i));
            glTexCoord2f( tc, 1.0 );
            glVertex3f(radius * cos(i), height, radius * sin(i));
        }
        /* close the loop back to zero degrees */
        glTexCoord2f( 0.0, 0.0 );
        glVertex3f(radius, 0, 0);
        glTexCoord2f( 0.0, 1.0 );
        glVertex3f(radius, height, 0);
    glEnd();
    glPopMatrix();
}
GLuint tex;
void init()
{
    unsigned char data[] =
    {
        128, 128, 128, 255,
        255, 0, 0, 255,
        0, 255, 0, 255,
        0, 0, 255, 255,
    };
    glGenTextures( 1, &tex );
    glBindTexture( GL_TEXTURE_2D, tex );
    glTexParameteri( GL_TEXTURE_2D, GL_TEXTURE_WRAP_S, GL_CLAMP_TO_EDGE );
    glTexParameteri( GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, GL_CLAMP_TO_EDGE );
    glTexParameteri( GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_NEAREST );
    glTexParameteri( GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_NEAREST );
    glTexImage2D( GL_TEXTURE_2D, 0,GL_RGBA, 2, 2, 0, GL_RGBA, GL_UNSIGNED_BYTE, data );
}
float angle = 0;
void timer( int value )
{
    angle += 6;
    glutPostRedisplay();
    glutTimerFunc( 16, timer, 0 );
}
void display()
{
    glClearColor( 0, 0, 0, 1 );
    glClear( GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT );
    glMatrixMode( GL_PROJECTION );
    glLoadIdentity();
    gluPerspective( 60, 1.0, 0.1, 100.0 );
    glMatrixMode( GL_MODELVIEW );
    glLoadIdentity();
    glTranslatef( 0, 0, -5 );
    glEnable( GL_CULL_FACE );
    glEnable( GL_DEPTH_TEST );
    glRotatef( angle, 0.2, 0.3, 0.1 );
    glEnable( GL_TEXTURE_2D );
    glBindTexture( GL_TEXTURE_2D, tex );
    cylinder();
    glutSwapBuffers();
}
int main(int argc, char **argv)
{
    glutInit( &argc, argv );
    glutInitDisplayMode( GLUT_RGBA | GLUT_DEPTH | GLUT_DOUBLE );
    glutInitWindowSize( 600, 600 );
    glutCreateWindow( "GLUT" );
    init();
    glutDisplayFunc( display );
    glutTimerFunc( 0, timer, 0 );
    glutMainLoop();
    return 0;
}

看起来您有一个功能性的解决方案。但与原始代码相比，我认为还有一些地方值得改进，所以我仍然想提供一个替代方案。它的地址：

• 它的效率非常低，使用了大量的sin/cos调用以及除法，这些都相当昂贵。下面的代码使用一个sin、一个cos和几个可以在编译时计算的除法。剩下的都是加法和乘法，它们的运算速度要快得多
• 原始代码使用浮点值进行循环控制。由于浮点值本质上是不精确的，这将或多或少地"随机"导致一次或多或少的迭代，这取决于舍入的计算方式
• 原始代码使用float、double和int类型的任意混合。float对坐标来说很好，不需要使用较慢的双精度，也不需要昂贵的类型转换回float

代码（未经测试，但希望足够接近以传达所提出的方法）：

// Number of segments a circle is divided into.
const unsigned DIV_COUNT = 32;
// Calculate angle increment from point to point, and its cos/sin.
float angInc = 2.0f * M_PI / static_cast<float>(DIV_COUNT);
float cosInc = cos(angInc);
float sinInc = sin(angInc);
// Draw top cap.
glBegin(GL_TRIANGLE_FAN);
glTexCoord2f(0.5f, 0.5f);
glVertex3f(0.0f, height, 0.0f);
glTexCoord2f(1.0f, 0.5f);
glVertex3f(radius, height, 0.0f);
float xc = 1.0f;
float yc = 0.0f;
for (unsigned iDiv = 1; iDiv < DIV_COUNT; ++iDiv) {
    float xcNew = cosInc * xc - sinInc * yc;
    yc = sinInc * xc + cosInc * yc;
    xc = xcNew;
    glTexCoord2f(0.5f + 0.5f * xc, 0.5f + 0.5f * yc);
    glVertex3f(radius * xc, height, -radius * yc);
}
glTexCoord2f(1.0f, 0.5f);
glVertex3f(radius, height, 0.0f);
glEnd();
// Draw bottom cap.
glBegin(GL_TRIANGLE_FAN);
glTexCoord2f(0.5f, 0.5f);
glVertex3f(0.0f, 0.0f, 0.0f);
glTexCoord2f(1.0f, 0.5f);
glVertex3f(radius, 0.0f, 0.0f);
xc = 1.0f;
yc = 0.0f;
for (unsigned iDiv = 1; iDiv < DIV_COUNT; ++iDiv) {
    float xcNew = cosInc * xc - sinInc * yc;
    yc = sinInc * xc + cosInc * yc;
    xc = xcNew;
    glTexCoord2f(0.5f + 0.5f * xc, 0.5f + 0.5f * yc);
    glVertex3f(radius * xc, 0.0f, radius * yc);
}
glTexCoord2f(1.0f, 0.5f);
glVertex3f(radius, 0.0f, 0.0f);
glEnd();
float texInc = 1.0f / static_cast<float>(DIV_COUNT);
// Draw cylinder.
glBegin(GL_TRIANGLE_STRIP);
glTexCoord2f(0.0f, 0.0f);
glVertex3f(radius, 0.0f, 0.0f);
glTexCoord2f(0.0f, 1.0f);
glVertex3f(radius, height, 0.0f);
xc = 1.0f;
yc = 0.0f;
float texCoord = 0.0f;
for (unsigned iDiv = 1; iDiv < DIV_COUNT; ++iDiv) {
    float xcNew = cosInc * xc - sinInc * yc;
    yc = sinInc * xc + cosInc * yc;
    xc = xcNew;
    texCoord += texInc;
    glTexCoord2f(texCoord, 0.0f);
    glVertex3f(radius * xc, 0.0f, radius * yc);
    glTexCoord2f(texCoord, 1.0f);
    glVertex3f(radius * xc, height, radius * yc);
}
glTexCoord2f(0.0f, 0.0f);
glVertex3f(radius, 0.0f, 0.0f);
glTexCoord2f(0.0f, 1.0f);
glVertex3f(radius, height, 0.0f);
glEnd();

如果您有兴趣使用现代OpenGL，我对这个问题的回答将展示如何使用VBO绘制圆：如何在ES2.0中使用VBO来绘制圆。