OpenGL多边形渲染模式和纹理映射

Question

之前问了一个关于我的项目的问题，但似乎我对 openGL 的了解比我目前所做的更多，但我得到的答案是在补充我的知识，所以提前感谢！

好的，目前我的汽车形状是使用 GL_LINE_LOOP 绘制的，看起来像这样。

我想映射到车身上的图像如下所示。

我知道我的形状图片并不完美，但我试图将那张图片放在我的线条中，以便它至少给人留下汽车模型的一些印象。我已经尝试使用以下代码：

void drawBody(int textureindex)
{
glEnable(GL_TEXTURE_2D);
glBindTexture(GL_TEXTURE_2D, textureLib[textureindex]);

glBegin(GL_POLYGON);

glTexCoord2f(0.0F, 0.0F);
glVertex2f(-1.0f, 0.0f);
glTexCoord2f(-0.97, 0.0);
glVertex2f(-1.97f, 0.0f);
//wheel arch begin.
glTexCoord2f(-0.93, 0.3);
glVertex2f(-1.93f, 0.3f);
glTexCoord2f(-0.95, 0.4);
glVertex2f(-1.95f, 0.4f);
glTexCoord2f(-1.2, 0.6);
glVertex2f(-2.2f, 0.6f);
glTexCoord2f(-1.6, 0.6);
glVertex2f(-2.6f, 0.6f);
glTexCoord2f(-1.82, 0.4);
glVertex2f(-2.82f, 0.4f);
glTexCoord2f(-1.8, 0.3);
glVertex2f(-2.8f, 0.3f);
glTexCoord2f(-1.78, 0.0);
glVertex2f(-2.78f, 0.0f);
//end wheel arch.
//Front of car.
glTexCoord2f(-2.8, 0.0);
glVertex2f(-3.8f, 0.0f);
glTexCoord2f(-2.7, 0.2);
glVertex2f(-3.7f, 0.2f);
glTexCoord2f(-2.8, 0.4);
glVertex2f(-3.8f, 0.4f);
glTexCoord2f(-1.8, 0.7);
glVertex2f(-2.8f, 0.7f);
glTexCoord2f(-1.4, 0.7);
glVertex2f(-2.4f, 0.7f);
//Windscreen.
glTexCoord2f(0.0, 1.0);
glVertex2f(-1.0f, 1.0f);
glTexCoord2f(1.5, 1.05);
glVertex2f(0.5f, 1.05f);
glTexCoord2f(3.3, 0.8);
glVertex2f(2.3f, 0.8f);
//rear bumper.
glTexCoord2f(3.15, 0.5);
glVertex2f(2.15f, 0.5f);
glTexCoord2f(3.15, 0.3);
glVertex2f(2.15f, 0.3f);
glTexCoord2f(3.35, 0.3);
glVertex2f(2.35f, 0.3f);
glTexCoord2f(3.0, 0.0);
glVertex2f(2.0f, 0.0f);
glTexCoord2f(2.83, 0.0);
glVertex2f(1.83f, 0.0f);
//wheel arch begin.
glTexCoord2f(2.85, 0.3);
glVertex2f(1.85f, 0.3f);
glTexCoord2f(2.86, 0.4);
glVertex2f(1.86f, 0.4f);
glTexCoord2f(2.6, 0.6);
glVertex2f(1.6f, 0.6f);
glTexCoord2f(2.2, 0.6);
glVertex2f(1.2f, 0.6f);
glTexCoord2f(2.0, 0.4);
glVertex2f(1.0f, 0.4f);
glTexCoord2f(2.0, 0.3);
glVertex2f(1.0f, 0.3f);
glTexCoord2f(2.05, 0.0);
glVertex2f(1.05f, 0.0f);
//end wheel arch.
glEnd();
glDisable(GL_TEXTURE_2D);
}

这导致了这种可怕的情况

两个问题。一是很明显我的纹理坐标确实是错误的，其次我不知道如何阻止多边形模式摆脱轮拱：/在这两个方面的帮助将不胜感激:)

Answer 1

纹理坐标应在 [0, 1] 范围内。

轮拱问题是因为 OpenGL 只渲染凸多边形。使用tessellation facilities 将凹多边形转换为三角形网格。

P.S.：对于 OpenGL 的即时模式，我建议您采用更易于阅读和维护的不同编码风格：

void drawBody(int textureindex)
{
    glEnable(GL_TEXTURE_2D);
    glBindTexture(GL_TEXTURE_2D, textureLib[textureindex]);

    glBegin(GL_POLYGON);

    glTexCoord2f( 0.0 , 0.0 ); glVertex2f(-1.0 , 0.0 );
    glTexCoord2f(-0.97, 0.0 ); glVertex2f(-1.97, 0.0 );

    // Wheel arch
    glTexCoord2f(-0.93, 0.3 ); glVertex2f(-1.93, 0.3 );
    glTexCoord2f(-0.95, 0.4 ); glVertex2f(-1.95, 0.4 );
    glTexCoord2f(-1.2 , 0.6 ); glVertex2f(-2.2 , 0.6 );
    glTexCoord2f(-1.6 , 0.6 ); glVertex2f(-2.6 , 0.6 );
    glTexCoord2f(-1.82, 0.4 ); glVertex2f(-2.82, 0.4 );
    glTexCoord2f(-1.8 , 0.3 ); glVertex2f(-2.8 , 0.3 );
    glTexCoord2f(-1.78, 0.0 ); glVertex2f(-2.78, 0.0 );

    // Front of car
    glTexCoord2f(-2.8 , 0.0 ); glVertex2f(-3.8 , 0.0 );
    glTexCoord2f(-2.7 , 0.2 ); glVertex2f(-3.7 , 0.2 );
    glTexCoord2f(-2.8 , 0.4 ); glVertex2f(-3.8 , 0.4 );
    glTexCoord2f(-1.8 , 0.7 ); glVertex2f(-2.8 , 0.7 );
    glTexCoord2f(-1.4 , 0.7 ); glVertex2f(-2.4 , 0.7 );

    // Windscreen
    glTexCoord2f( 0.0 , 1.0 ); glVertex2f(-1.0 , 1.0 );
    glTexCoord2f( 1.5 , 1.05); glVertex2f( 0.5 , 1.05);
    glTexCoord2f( 3.3 , 0.8 ); glVertex2f( 2.3 , 0.8 );

    // Rear bumper
    glTexCoord2f( 3.15, 0.5 ); glVertex2f( 2.15, 0.5 );
    glTexCoord2f( 3.15, 0.3 ); glVertex2f( 2.15, 0.3 );
    glTexCoord2f( 3.35, 0.3 ); glVertex2f( 2.35, 0.3 );
    glTexCoord2f( 3.0 , 0.0 ); glVertex2f( 2.0 , 0.0 );
    glTexCoord2f( 2.83, 0.0 ); glVertex2f( 1.83, 0.0 );

    // Wheel arch
    glTexCoord2f( 2.85, 0.3 ); glVertex2f( 1.85, 0.3 );
    glTexCoord2f( 2.86, 0.4 ); glVertex2f( 1.86, 0.4 );
    glTexCoord2f( 2.6 , 0.6 ); glVertex2f( 1.6 , 0.6 );
    glTexCoord2f( 2.2 , 0.6 ); glVertex2f( 1.2 , 0.6 );
    glTexCoord2f( 2.0 , 0.4 ); glVertex2f( 1.0 , 0.4 );
    glTexCoord2f( 2.0 , 0.3 ); glVertex2f( 1.0 , 0.3 );
    glTexCoord2f( 2.05, 0.0 ); glVertex2f( 1.05, 0.0 );

    glEnd();
    glDisable(GL_TEXTURE_2D);
}