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我是 OpenGL 的初学者，作为我的第一个应用程序，我尝试使用三角形的重心细分方法生成分形。不知道 OpenGL 用于透视改变的功能，我对缩放和改变视点算法的第一个想法是每次按下键时用不同的起点坐标和缩放因子简单地重绘整个分形（用于相机移动的箭头和 +/ - 用于缩放）。

鉴于重心细分的 6 次迭代大约绘制了 56 000 个三角形（6^0+6^1+6^2+6^3+6^4+6^5+6^6 三角形），该算法非常效率低下。所以我尝试使用 gluPerspective() 进行缩放，结果遗憾的是黑屏，而不是分形。我有两个主要问题：

  • 用于透视变化和视点的 OpenGL 函数（gluPerspective()、gluLookAt()、glFrustum() 等）是用不同的坐标重新绘制整个图形，还是使用更有效的方法来获得相同的结果？在我的情况下，它们的使用会更有效吗？

  • 我在代码中做错了什么。为什么我会黑屏？

    #include <GL/glfw.h>
#include <iostream>
#include <math.h>

using namespace std;

struct punct{ GLdouble x, y;}; //"punct" means "point" in my native language
punct A, B, C;
int n=0, mode=1;
double l=1.6, ox=0, oy=0, scale=1;

punct mid (punct A, punct B);
void initiate ();
void line (punct A, punct B);
void triangle (punct A, punct B, punct C);
void divide (punct A, punct B, punct C,int i);

int main ()
{
    int     width, height;
    bool    running = true;
    char input=NULL;

    glfwInit();

    if( !glfwOpenWindow( 800, 800, 0, 0, 0, 0, 0, 0, GLFW_FULLSCREEN ) )
    {
        glfwTerminate();
        return 0;
    }

    glfwSetWindowTitle("Baricentric");

    while(running)
    {
        glfwGetWindowSize( &width, &height );
        height = height > 0 ? height : 1;

        glViewport( 0, 0, width, height );

        glClearColor( 0.0f, 0.0f, 0.0f, 0.0f );
        glClear( GL_COLOR_BUFFER_BIT );

        //This functions make my screen black 
        //glMatrixMode(GL_MODELVIEW);
        //glLoadIdentity();
        //gluPerspective (50*scale, width/height, 10.0, 100.0); 

        initiate ();

        if(glfwGetKey(GLFW_KEY_KP_ADD) && glfwGetKey(GLFW_KEY_LCTRL)) input='+';
        if(!glfwGetKey(GLFW_KEY_KP_ADD) && input=='+') {
        if(n<7) n++;
        input='\n';
        }
        if(glfwGetKey(GLFW_KEY_KP_SUBTRACT) && glfwGetKey(GLFW_KEY_LCTRL)) input='-';
        if(!glfwGetKey(GLFW_KEY_KP_SUBTRACT) && input=='-') {
            if(n>0)n--;
            input='\n';
        }

        if(glfwGetKey(GLFW_KEY_KP_1)||glfwGetKey('1')) input='1';
        if(!glfwGetKey(GLFW_KEY_KP_1) && input=='1') {
            mode=1;
            input='\n';
        }

        if(glfwGetKey(GLFW_KEY_KP_0)||glfwGetKey('0')) input='0';
        if(!glfwGetKey(GLFW_KEY_KP_0) && input=='0') {
            mode=0;
            input='\n';
        }

        if(glfwGetKey(GLFW_KEY_KP_ADD) && !glfwGetKey(GLFW_KEY_LCTRL)) l+=0.002*(n+0.5); //'l' is replaced with 'scale' when using gluPerspective()
        if(glfwGetKey(GLFW_KEY_KP_SUBTRACT) && !glfwGetKey(GLFW_KEY_LCTRL)) l-=0.002*(n+0.5); //'l' is replaced with 'scale' when using gluPerspective()
        if(glfwGetKey(GLFW_KEY_UP)) oy-=0.002*(n+0.5);
        if(glfwGetKey(GLFW_KEY_DOWN)) oy+=0.002*(n+0.5);
        if(glfwGetKey(GLFW_KEY_RIGHT)) ox+=0.002*(n+0.5);
        if(glfwGetKey(GLFW_KEY_LEFT)) ox-=0.002*(n+0.5);


        if (n) divide (A,B,C,1);


        glfwSwapBuffers();

        running = !glfwGetKey(GLFW_KEY_ESC) && glfwGetWindowParam( GLFW_OPENED);
    }

    glfwTerminate();

    return 0;
}

punct mid (punct A, punct B) {
    punct C;
    C.x=(A.x+B.x)/2;
    C.y=(A.y+B.y)/2;
    return C;
}

void initiate () {

    A.x = -(l/2)+ox; A.y = -(l*sqrt(3)/4)+oy;
    B.x = l/2+ox; B.y = A.y;
    C.x = 0+ox; C.y = (l*sqrt(3)/4)+oy;

    glBegin (GL_QUADS);
        glColor3f(0.93,0.84,0.82); glVertex3d(-1, 1, 0);
        glColor3f(0.01,0.95,0.83); glVertex3d(-1, -1, 0);
        glColor3f(0.80,0.71,0.80); glVertex3d(1, -1, 0);
        glColor3f(0.8,1,0.8); glVertex3d(1, 1, 0);
    glEnd ();

    glBegin (GL_TRIANGLES);
        glColor3f(0,0.6,0.88); glVertex3d(C.x, C.y, 0);
        glColor3f(0,0.77,0.73); glVertex3d(B.x, B.y, 0);
        glColor3f(0.01,0.66,0.62); glVertex3d(A.x, A.y, 0);
    glEnd ();

    if (mode==0) {
        glLineWidth (0.1);
        glColor3f(0,0,0.36);
        glBegin (GL_LINE_LOOP);
            glVertex3d(C.x, C.y, 0);
            glVertex3d(B.x, B.y, 0);
            glVertex3d(A.x, A.y, 0);
        glEnd ();
    }
}


void divide (punct A, punct B, punct C, int i) {
    if(i<=n) {
        punct a, b, c, G;
        c=mid(A,B);
        b=mid(A,C);
        a=mid(B,C);
        G.x=(A.x+B.x+C.x)/3;
        G.y=(A.y+B.y+C.y)/3;
        if(mode==1) {
            triangle(G,a,C);
            triangle(G,b,C);
            triangle(G,a,B);
            triangle(G,c,B);
            triangle(G,c,A);
            triangle(G,b,A);
        }
        line(c,C);
        line(a,A);
        line(b,B);
        divide(G,a,C,i+1);
        divide(G,b,C,i+1);
        divide(G,a,B,i+1);
        divide(G,c,B,i+1);
        divide(G,c,A,i+1);
        divide(G,b,A,i+1);
    }

}

void line (punct A, punct B) {
    glBegin (GL_LINE_STRIP);
        glVertex3d(A.x,A.y,0);
        glVertex3d(B.x,B.y,0);
    glEnd ();
}

void triangle (punct A, punct B, punct C) {
    glBegin (GL_TRIANGLES);
        glColor3f(0,0.6,0.88); glVertex3d(C.x, C.y, 0);
        glColor3f(0,0.77,0.73); glVertex3d(B.x, B.y, 0);
        glColor3f(0.01,0.66,0.62); glVertex3d(A.x, A.y, 0);
    glEnd ();
}
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1 回答 1

3

像以前的许多人一样，您已经误以为 OpenGL 是一个场景图。不是这种情况。

OpenGL 是一个绘图 API。您的操作系统提供了一个画布（窗口、PBuffer、Pixmap 等），而 OpenGL 提供了点、线或三角形形式的绘图工具。

用于透视变化和视点的OpenGL函数（gluPerspective（），gluLookAt（），glFrustum（）等）是否用不同的坐标重绘整个图形，

他们所做的只是改变一些矩阵的值。屏幕上的任何内容都不会因此而改变。您必须重新绘制整个事物才能做出可见的更改。

于 2013-05-30T20:35:03.170 回答