OpenGL多边形渲染模式和纹理映射

Question

早些时候问了一个关于我的项目的问题，但似乎我对 openGL 的了解比我现在知道的少得多，但我得到的答案都在丰富我的知识，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，如下所示。

我想要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，但我试图将图片放入我的线条中这样它至少能给汽车建模留下一些印象。我尝试使用以下代码：

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);
}

这导致了这个可怕的

两个问题。一是很明显我的纹理坐标确实是错误的，二是我不知道如何阻止多边形模式摆脱轮拱：/将不胜感激这两个方面的帮助:)

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。使用曲面细分工具将凹多边形转换为三角形网格。

PS：对于OpenGL的立即模式，我建议您采用不同的编码风格，这样更容易阅读和维护：

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);
}