任何人都可以解释以下opengl代码吗？

Question

谁能解释一下函数调用时glvertex3fv是如何工作的

GLfloat v[][8][3]={{{-1.5,-1.5,-1.0}, {-1.3,-1.5,-1.0}, {-1.3,-1.3,-1.0}, {-1.5,-1.3,-1.0}, {-1.6,-1.6,1.0}, {-1.4,-1.6,1.0}, {-1.4,-1.4,1.0}, {-1.6,-1.4,1.0}} ,

{{-1.3,-1.5,-1.0}, {-1.1,-1.5,-1.0}, {-1.1,-1.3,-1.0}, {-1.3,-1.3,-1.0}, {-1.4,-1.6,1.0}, {-1.2,-1.6,1.0}, {-1.2,-1.4,1.0}, {-1.4,-1.4,1.0}} ,

{{-1.1,-1.5,-1.0}, {-0.9,-1.5,-1.0}, {-0.9,-1.3,-1.0}, {-1.1,-1.3,-1.0}, {-1.2,-1.6,1.0}, {-1.0,-1.6,1.0}, {-1.0,-1.4,1.0}, {-1.2,-1.4,1.0}} ,

{{-1.5,-1.3,-1.0}, {-1.3,-1.3,-1.0}, {-1.3,-1.1,-1.0}, {-1.5,-1.1,-1.0}, {-1.6,-1.4,1.0}, {-1.4,-1.4,1.0}, {-1.4,-1.2,1.0}, {-1.6,-1.2,1.0}} ,

{{-1.3,-1.3,-1.0}, {-1.1,-1.3,-1.0}, {-1.1,-1.1,-1.0}, {-1.3,-1.1,-1.0}, {-1.4,-1.4,1.0}, {-1.2,-1.4,1.0}, {-1.2,-1.2,1.0}, {-1.4,-1.2,1.0}} ,

{{-1.1,-1.3,-1.0}, {-0.9,-1.3,-1.0}, {-0.9,-1.1,-1.0}, {-1.1,-1.1,-1.0}, {-1.2,-1.4,1.0}, {-1.0,-1.4,1.0}, {-1.0,-1.2,1.0}, {-1.2,-1.2,1.0}} ,

{{-1.5,-1.1,-1.0}, {-1.3,-1.1,-1.0}, {-1.3,-0.9,-1.0}, {-1.5,-0.9,-1.0}, {-1.6,-1.2,1.0}, {-1.4,-1.2,1.0}, {-1.4,-1.0,1.0}, {-1.6,-1.0,1.0}} ,

{{-1.3,-1.1,-1.0}, {-1.1,-1.1,-1.0}, {-1.1,-0.9,-1.0}, {-1.3,-0.9,-1.0}, {-1.4,-1.2,1.0}, {-1.2,-1.2,1.0}, {-1.2,-1.0,1.0}, {-1.4,-1.0,1.0}} ,

{{-1.1,-1.1,-1.0}, {-0.9,-1.1,-1.0}, {-0.9,-0.9,-1.0}, {-1.1,-0.9,-1.0}, {-1.2,-1.2,1.0}, {-1.0,-1.2,1.0}, {-1.0,-1.0,1.0}, {-1.2,-1.0,1.0}}};

GLfloat colors[][3]={{0.0,0.0,0.0}, //black

{1.0,0.0,0.0}, //red

{1.0,1.0,0.0}, //yellow

{0.0,1.0,0.0}, //green

{1.0,0.0,1.0}, //magenta

{0.0,1.0,1.0}}; //cyan ....

void polygon(int a,int b,int c,int d,int i)

{

glBegin(GL_POLYGON);

glColor3fv(colors[a]);

glVertex3fv(v[i][a]); //wt is the meaning of this line

glColor3fv(colors[b]);

glVertex3fv(v[i][b]);

glColor3fv(colors[c]);

glVertex3fv(v[i][c]);

glColor3fv(colors[d]);

glVertex3fv(v[i][d]);

glFlush();

glEnd(); }

void colorcube() {

polygon(0,3,2,1,i); //wt is the meaning of i

polygon(2,3,7,6,i);

polygon(0,4,7,3,i);

polygon(1,2,6,5,i);

polygon(4,5,6,7,i);

polygon(0,1,5,4,i);

}

Answer 1

注意：这是 OpenGL 即时绘图模式。它已被弃用和不鼓励使用近 20（！）年。 1996 年，OpenGL-1.1 引入了顶点数组，从那时起它就比立即模式更受欢迎。

glVertex 是旧的、已弃用的 OpenGL 即时绘图模式的一部分。在 glBegin ... glEnd 块之间，任意数量的 glVertex 调用用于将图元绘制到屏幕上；控制所绘制内容的属性 glVertex 调用之前的任何属性设置调用“选择”glVertex 随后将发出的内容。

顶点是为其指定的任何属性+其位置的全部组合。

首先让我们看一下单点：

glBegin(GL_POINTS); /* for every call of glVertex draw a point */

/* tip the "pen" into a bucket of bright red */
glColor3f(1,0,0);
/* draw a point, with whatever color currently is set at 1,1,1 */
glVertex3f(1,1,1);

/* let's make the pen blue */
glColor3f(0,0,1);

/* wait, we want it to be green */
glColor3f(0,1,0);
/* only the last value set for an attribute matters.
 * so the point drawn at 0,1,0 will be green */
glVertex3f(0,1,0);

/* and so on */
/* ... */

glEnd();

将 GL_POINTS 绘制到 GL_LINES 或 GL_TRIANGLES 的不同之处在于，您必须发射顶点对或三元组才能实际出现在屏幕上（所有这些都带有 glBegin、glEnd 块）。

现在，您通常会将属性数据包含在一些较大的内存缓冲区中。在这种情况下，将属性设置器函数指向该内存而不是传递参数更有意义。这由 OpenGL 调用名称中的字母“v”表示。所以

GLfloat red_green_blue[3][3] = {
   {1,0,0},
   {0,1,0},
   {0,0,1}
};

glColor3fv(red_green_blue[0]) /* points to the 'red' part */

这相当于

glColor3f(
    red_green_blue[0][0],
    red_green_blue[0][1],
    red_green_blue[0][2] );

显然，'v' 形式更短且更易于阅读。

现在，在您的代码中，这一切都归结为从多维数组中取消引用位置。你想知道“我”是什么意思。我建议你用铅笔在一张纸上按照代码进行操作，然后弄清楚哪些值会以何种方式进入 OpenGL。