纹理坐标不起作用？

Question

说真的，我对这段代码感到生气，因为不行：

switch(particle) {
case 0:
    glBegin(GL_TRIANGLE_STRIP);         // STONE
        glNormal3f(0.0f, 0.0f, 1.0f);
        glTexCoord2d(1, 1); glVertex3f(x+size, y+size, 0.0f); // Top Right
        glTexCoord2d(0.5, 1); glVertex3f(x-size, y+size, 0.0f); // Top Left
        glTexCoord2d(1, 0.5); glVertex3f(x+size, y-size, 0.0f); // Bottom Right
        glTexCoord2d(0.5, 0.5); glVertex3f(x-size, y-size, 0.0f); // Bottom Left
    glEnd();
    break;
case 1:
    glBegin(GL_TRIANGLE_STRIP);         // EARTH
        glNormal3f(0.0f, 0.0f, 1.0f);
        glTexCoord2d(0.5, 0.5); glVertex3f(x+size, y+size, 0.0f); // Top Right
        glTexCoord2d(0, 0.5); glVertex3f(x-size, y+size, 0.0f); // Top Left
        glTexCoord2d(0.5, 0); glVertex3f(x+size, y-size, 0.0f); // Bottom Right
        glTexCoord2d(0, 0); glVertex3f(x-size, y-size, 0.0f); // Bottom Left
    glEnd();
    break;
}

案例0工作正常，但案例1没有，我不知道为什么... 这是图像（32x32，带有两个16x16子纹理）：

Answer 1

给那个案例0显然工作正常，案例1的纹理坐标是错误的。他们应该是：

glBegin(GL_TRIANGLE_STRIP);         // EARTH
    glNormal3f(0.0f, 0.0f, 1.0f);
    glTexCoord2d(0.5, 1.0); glVertex3f(x+size, y+size, 0.0f); // Top Right
    glTexCoord2d(0, 1.0); glVertex3f(x-size, y+size, 0.0f); // Top Left
    glTexCoord2d(0.5, 0.5); glVertex3f(x+size, y-size, 0.0f); // Bottom Right
    glTexCoord2d(0, 0.5); glVertex3f(x-size, y-size, 0.0f); // Bottom Left
glEnd();