切换到 freeglut 后线条不渲染

Posted 2023-02-22

【中文标题】切换到 freeglut 后线条不渲染

【英文标题】：lines not rendering after switching to freeglut

【发布时间】：2013-05-25 16:14:41

【问题描述】：

我有一个项目，我正在使用 glut - 但是我去释放 glut 为了能够使用

glutBitmapCharacter

但是当我这样做时，我用来绘制网格的方法不再有效

//This creates the grid 
    for(float f = -1;f<1; f+=0.05)
    glBegin(GL_LINE_STRIP);
        glVertex2f(f,-1);
        glVertex2f(f,1);
        glEnd();
        glBegin(GL_LINE_STRIP);
        glVertex2f(-1,f);
        glVertex2f(1,f);
        glEnd();
    

全班：

   #include<stdlib.h>
    #include<windows.h>
    #include<GL/glut.h>
    #include<GL/freeglut.h>
    #include<iostream>
    #include <vector>
    #include "include/Block.h"
    #include <string>


    using namespace std;

    void drawBitmapText(char *string, float x, float y, float z);
    void reshape(int w, int h);
    void render(void);
    void keyboard(unsigned char c,int x,int y);
    void mouse(int button,int state, int x, int y);


    vector <Block> blockList;
    int screenXSize=800;
    int screenYSize=800;
    int selectedBlockType = 0;
    int main(int argc, char ** argv)


    blockList.push_back(*new Block(0,1,1));

    Block Test = blockList.at(0);
    string s = Test.getName();



    glutInit(&argc,argv);
    glutInitDisplayMode(GLUT_DEPTH | GLUT_DOUBLE | GLUT_RGBA);
    glutInitWindowPosition(100,100);
    glutInitWindowSize(screenXSize,screenYSize);
    glutCreateWindow("TITLE");
    glutDisplayFunc(render);
    glutReshapeFunc(reshape);
    glutKeyboardFunc(keyboard);
    glutMouseFunc(mouse);
    glutMainLoop();








    
    void mouse(int button,int state, int x, int y)
        if(button==GLUT_RIGHT_BUTTON)


        
         if(button==GLUT_LEFT_BUTTON)


        

    
    void keyboard(unsigned char c,int x,int y)
        if (c==27)
            exit(0);
        

    
void reshape(int w, int h)

   glViewport (0, 0, (GLsizei) w, (GLsizei) h); 
   glMatrixMode (GL_PROJECTION); 
   glLoadIdentity (); ...

   gluOrtho2D (0.0, (GLdouble) w, 0.0, (GLdouble) h);

void drawBitmapText(char *string, float x, float y, float z)

    char *c;
    glRasterPos3f(x, y, z);

    for (c=string; *c != '\0'; c++)
    
        glutBitmapCharacter(GLUT_BITMAP_TIMES_ROMAN_24, *c);
    

    void render(void)

    glClear(GL_COLOR_BUFFER_BIT|GL_DEPTH_BUFFER_BIT);


    drawBitmapText("CAN YOU READ ME?",200,200,0);




    //This creates the grid 
    for(float f = -1;f<1; f+=0.05)
    glBegin(GL_LINE_STRIP);
        glVertex3f(f,-1);
        glVertex3f(f,1);
        glEnd();
        glBegin(GL_LINE_STRIP);
        glVertex2f(-1,f);
        glVertex2f(1,f);
        glEnd();
    

非常感谢任何帮助

    glutSwapBuffers();

    glFlush();
    

但是我能够运行示例项目

/*
 * GLUT Shapes Demo
 *
 * Written by Nigel Stewart November 2003
 *
 * This program is test harness for the sphere, cone
 * and torus shapes in GLUT.
 *
 * Spinning wireframe and smooth shaded shapes are
 * displayed until the ESC or q key is pressed.  The
 * number of geometry stacks and slices can be adjusted
 * using the + and - keys.
 */

#ifdef __APPLE__
#include <GLUT/glut.h>
#else
#include <GL/glut.h>
#endif

#include <stdlib.h>

static int slices = 16;
static int stacks = 16;

/* GLUT callback Handlers */

static void resize(int width, int height)

    const float ar = (float) width / (float) height;

    glViewport(0, 0, width, height);
    glMatrixMode(GL_PROJECTION);
    glLoadIdentity();
    glFrustum(-ar, ar, -1.0, 1.0, 2.0, 100.0);

    glMatrixMode(GL_MODELVIEW);
    glLoadIdentity() ;


static void display(void)

    const double t = glutGet(GLUT_ELAPSED_TIME) / 1000.0;
    const double a = t*90.0;

    glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
    glColor3d(1,0,0);

    glPushMatrix();
        glTranslated(-2.4,1.2,-6);
        glRotated(60,1,0,0);
        glRotated(a,0,0,1);
        glutSolidSphere(1,slices,stacks);
    glPopMatrix();

    glPushMatrix();
        glTranslated(0,1.2,-6);
        glRotated(60,1,0,0);
        glRotated(a,0,0,1);
        glutSolidCone(1,1,slices,stacks);
    glPopMatrix();

    glPushMatrix();
        glTranslated(2.4,1.2,-6);
        glRotated(60,1,0,0);
        glRotated(a,0,0,1);
        glutSolidTorus(0.2,0.8,slices,stacks);
    glPopMatrix();

    glPushMatrix();
        glTranslated(-2.4,-1.2,-6);
        glRotated(60,1,0,0);
        glRotated(a,0,0,1);
        glutWireSphere(1,slices,stacks);
    glPopMatrix();

    glPushMatrix();
        glTranslated(0,-1.2,-6);
        glRotated(60,1,0,0);
        glRotated(a,0,0,1);
        glutWireCone(1,1,slices,stacks);
    glPopMatrix();

    glPushMatrix();
        glTranslated(2.4,-1.2,-6);
        glRotated(60,1,0,0);
        glRotated(a,0,0,1);
        glutWireTorus(0.2,0.8,slices,stacks);
    glPopMatrix();

    glutSwapBuffers();



static void key(unsigned char key, int x, int y)

    switch (key)
    
        case 27 :
        case 'q':
            exit(0);
            break;

        case '+':
            slices++;
            stacks++;
            break;

        case '-':
            if (slices>3 && stacks>3)
            
                slices--;
                stacks--;
            
            break;
    

    glutPostRedisplay();


static void idle(void)

    glutPostRedisplay();


const GLfloat light_ambient[]  =  0.0f, 0.0f, 0.0f, 1.0f ;
const GLfloat light_diffuse[]  =  1.0f, 1.0f, 1.0f, 1.0f ;
const GLfloat light_specular[] =  1.0f, 1.0f, 1.0f, 1.0f ;
const GLfloat light_position[] =  2.0f, 5.0f, 5.0f, 0.0f ;

const GLfloat mat_ambient[]    =  0.7f, 0.7f, 0.7f, 1.0f ;
const GLfloat mat_diffuse[]    =  0.8f, 0.8f, 0.8f, 1.0f ;
const GLfloat mat_specular[]   =  1.0f, 1.0f, 1.0f, 1.0f ;
const GLfloat high_shininess[] =  100.0f ;

/* Program entry point */

int main(int argc, char *argv[])

    glutInit(&argc, argv);
    glutInitWindowSize(640,480);
    glutInitWindowPosition(10,10);
    glutInitDisplayMode(GLUT_RGB | GLUT_DOUBLE | GLUT_DEPTH);

    glutCreateWindow("GLUT Shapes");

    glutReshapeFunc(resize);
    glutDisplayFunc(display);
    glutKeyboardFunc(key);
    glutIdleFunc(idle);

    glClearColor(1,1,1,1);
    glEnable(GL_CULL_FACE);
    glCullFace(GL_BACK);

    glEnable(GL_DEPTH_TEST);
    glDepthFunc(GL_LESS);

    glEnable(GL_LIGHT0);
    glEnable(GL_NORMALIZE);
    glEnable(GL_COLOR_MATERIAL);
    glEnable(GL_LIGHTING);

    glLightfv(GL_LIGHT0, GL_AMBIENT,  light_ambient);
    glLightfv(GL_LIGHT0, GL_DIFFUSE,  light_diffuse);
    glLightfv(GL_LIGHT0, GL_SPECULAR, light_specular);
    glLightfv(GL_LIGHT0, GL_POSITION, light_position);

    glMaterialfv(GL_FRONT, GL_AMBIENT,   mat_ambient);
    glMaterialfv(GL_FRONT, GL_DIFFUSE,   mat_diffuse);
    glMaterialfv(GL_FRONT, GL_SPECULAR,  mat_specular);
    glMaterialfv(GL_FRONT, GL_SHININESS, high_shininess);

    glutMainLoop();

    return EXIT_SUCCESS;

【参考方案1】：

问题是您的网格被 OpenGL 裁剪（丢弃），因为它位于视锥体之外。

在您的reshape 函数中，您将对象的区域设置为 x 方向的 (0, width) 和 (0, height ) 在 y 方向上调用gluOrtho2D。这本身不是问题，但您用于网格的坐标是 (-1,1)。如果您仔细观察窗口，您会看到左下角的像素亮起。

您需要做的最根本的事情是弄清楚您想要绘制到哪个空间。使用gluOrtho2D，您可以有效地在窗口坐标中进行渲染，因此如果您更新网格以从 [0, width] 进行渲染，而不是 [-1,1 ]，您的网格将与文本一样出现。相反，如果您想使用网格的坐标空间，请将gluOrtho2D 函数更新为gluOrtho2D( -1, 1, -1, 1 )，并将渲染文本的位置更新为该正方形内。

还有一个小问题，有一个名为GL_LINES 的基本类型，它将在每两个顶点之间绘制一条线段。在您的网格渲染循环中，您可以通过将循环编写为来提高效率

glBegin( GL_LINES );
for ( float f = -1; f < 1; f += 0.05 ) 
    glVertex2f( f, -1 );
    glVertex2f( f , 1 );
    glVertex2f( -1, f );
    glVertex2f(  1, f );

glEnd();

（哦，在你的例子中，你混合了glVertex2f，和glVertex3f[这是完全合法的OpenGL]，除了在你使用glVertex3f时，你只提供了两个导致语法错误的参数）

【讨论】：

非常感谢您的回答 - 作为旁注，我之前尝试过类似于您的循环的方法，但它崩溃了。这仍然会发生在您的循环版本中。

不客气。至于循环，你确定你没有使用glVertex*fv 版本吗？这些函数需要一个单一的指针值，所以如果你传入一个数值，你很容易崩溃。