c - 如何使opengl文本可见/改变颜色？

Question

我正在使用 openGL 做一个关于构造实体几何的迷你项目。我正在尝试创建两个窗口，第一个窗口显示我的名字、学院名称和其他详细信息，第二个窗口将显示实体几何窗口。我的第二个屏幕工作得很好，我可以在第一个屏幕上打印文本，但由于背景是黑色的，文本应该有不同的颜色，但它只是黑色，所以不可见。下面是代码，可以有人检查我的代码并告诉我错误在哪里。

#include<GL/glut.h>
#include<stdlib.h>
#include<stdio.h>
#include<string.h>
#include<math.h>
#include<GL/gl.h>

int isMainScreen=1;
enum {
  CSG_A, CSG_B, CSG_A_OR_B, CSG_A_AND_B, CSG_A_SUB_B, CSG_B_SUB_A
};

/* just draw single object */
void one(void (*a) (void))
{
  glEnable(GL_DEPTH_TEST);
  a();
  glDisable(GL_DEPTH_TEST);
}
/* "or" is easy; simply draw both objects with depth buffering on */
void or(void (*a) (void), void (*b) (void))
{
  glEnable(GL_DEPTH_TEST);
  a();
  b();
  glDisable(GL_DEPTH_TEST);
} 
/* Set stencil buffer to show the part of a (front or back face) that's inside b's volume. Requirements: GL_CULL_FACE enabled, depth func GL_LESS Side effects: depth test, stencil func, stencil op */
void
firstInsideSecond(void (*a) (void), void (*b) (void), GLenum face, GLenum test)
{
  glEnable(GL_DEPTH_TEST);
  glColorMask(GL_FALSE, GL_FALSE, GL_FALSE, GL_FALSE);
  glCullFace(face);     /* controls which face of a to use */
  a();                           /* draw a face of a into depth buffer */
  /* use stencil plane to find parts of a in b */
  glDepthMask(GL_FALSE);
  glEnable(GL_STENCIL_TEST);
  glStencilFunc(GL_ALWAYS, 0, 0);
  glStencilOp(GL_KEEP, GL_KEEP, GL_INCR);
  glCullFace(GL_BACK);
  b();                  /* increment the stencil where the front face of b is drawn */
  glStencilOp(GL_KEEP, GL_KEEP, GL_DECR);
  glCullFace(GL_FRONT);
  b();                  /* decrement the stencil buffer where the back face of b is drawn */
  glDepthMask(GL_TRUE);
  glColorMask(GL_TRUE, GL_TRUE, GL_TRUE, GL_TRUE);
  glStencilFunc(test, 0, 1);
  glDisable(GL_DEPTH_TEST);
  glCullFace(face);
  a();                  /* draw the part of a that's in b */
}

void
fixDepth(void (*a) (void))
{
  glColorMask(GL_FALSE, GL_FALSE, GL_FALSE, GL_FALSE);
  glEnable(GL_DEPTH_TEST);
  glDisable(GL_STENCIL_TEST);
  glDepthFunc(GL_ALWAYS);
  a();                  /* draw the front face of a, fixing the depth buffer */
  glDepthFunc(GL_LESS);
}
/* "and" two objects together */
void
and(void (*a) (void), void (*b) (void))
{
  firstInsideSecond(a, b, GL_BACK, GL_NOTEQUAL);
  fixDepth(b);
  firstInsideSecond(b, a, GL_BACK, GL_NOTEQUAL);
  glDisable(GL_STENCIL_TEST);  /* reset things */
}
/* subtract b from a */
void
sub(void (*a) (void), void (*b) (void))
{
  firstInsideSecond(a, b, GL_FRONT, GL_NOTEQUAL);
  fixDepth(b);
  firstInsideSecond(b, a, GL_BACK, GL_EQUAL);
  glDisable(GL_STENCIL_TEST);  /* reset things */
}

enum {
  SPHERE = 1, CONE
};

/* Draw a cone */
GLfloat coneX = 0.f, coneY = 0.f, coneZ = 0.f;
void
cone(void)
{
  glPushMatrix();
  glTranslatef(coneX, coneY, coneZ);
  glTranslatef(0.f, 0.f, -30.f);
  glCallList(CONE);
  glPopMatrix();
}

/* Draw a sphere */
GLfloat sphereX = 0.f, sphereY = 0.f, sphereZ = 0.f;
void
sphere(void)
{
  glPushMatrix();
  glTranslatef(sphereX, sphereY, sphereZ);
  glCallList(SPHERE);
  glPopMatrix();
}
int csg_op = CSG_A;

/* add menu callback */
void 
menu(int csgop)
{
  csg_op = csgop;
  glutPostRedisplay();
}

GLfloat viewangle;
void redraw(void)
{
  /* clear stencil each time */
 glClear(GL_COLOR_BUFFER_BIT|GL_DEPTH_BUFFER_BIT|GL_STENCIL_BUFFER_BIT);
  glPushMatrix();
  glRotatef(viewangle, 0.f, 1.f, 0.f);
  switch (csg_op) {
  case CSG_A:    one(cone);
                break;
  case CSG_B:    one(sphere);
                        break;

  case CSG_A_OR_B:    or(cone, sphere);
                    break;
  case CSG_A_AND_B:    and(cone, sphere);
                       break;
  case CSG_A_SUB_B:    sub(cone, sphere);
      break;
  case CSG_B_SUB_A:    sub(sphere, cone);
       break;
  }
  glPopMatrix();
  glutSwapBuffers();
}
/* animate scene by rotating */
enum {
  ANIM_LEFT, ANIM_RIGHT
};
int animDirection = ANIM_LEFT;

void 
anim(void)
{
  if (animDirection == ANIM_LEFT)
    viewangle -= 3.f;
  else
    viewangle += 3.f;
  glutPostRedisplay();
}

/* ARGSUSED1 */
/* special keys, like array and F keys */
void 
special(int key, int x, int y)
{
  switch (key) {
  case GLUT_KEY_LEFT:    glutIdleFunc(anim);
                            animDirection = ANIM_LEFT;
            break;
  case GLUT_KEY_RIGHT:    glutIdleFunc(anim);
                      animDirection = ANIM_RIGHT;
                      break;
  case GLUT_KEY_UP:
  case GLUT_KEY_DOWN:
                    glutIdleFunc(0);
                    break;
  }
}
/* ARGSUSED1 */
void 
key(unsigned char key, int x, int y)
{
  switch (key) {
  case 'a': viewangle -= 10.f;
    glutPostRedisplay();
                break;
  case 's':
    viewangle += 10.f;
    glutPostRedisplay();
    break;
    case '\13':
        isMainScreen=1;
        break;
        mydisplay();
    case '\033':
    exit(0);
}
}

int picked_object;
int xpos = 0, ypos = 0;
int newxpos, newypos;
int startx, starty;

void
mouse(int button, int state, int x, int y)
{
  if (state == GLUT_UP) {
    picked_object = button;
    xpos += newxpos;
    ypos += newypos;
    newxpos = 0;
    newypos = 0;
  } else {              /* GLUT_DOWN */
    startx = x;
    starty = y;
  }
}
#define DEGTORAD (2 * 3.1415 / 360)
void 
motion(int x, int y)
{
  GLfloat r, objx, objy, objz;

  newxpos = x - startx;
  newypos = starty - y;

  r = (newxpos + xpos) * 50.f / 512.f;
  objx = r * cos(viewangle * DEGTORAD);
  objy = (newypos + ypos) * 50.f / 512.f;
  objz = r * sin(viewangle * DEGTORAD);

  switch (picked_object) {
  case CSG_A:
    coneX = objx;
    coneY = objy;
    coneZ = objz;
    break;
  case CSG_B:
    sphereX = objx;
    sphereY = objy;
    sphereZ = objz;
    break;
  }
  glutPostRedisplay();
}

void drawString1(float x, float y, float z, char * string) {
    char * c;
    glRasterPos3f(x, y, z);
    for (c = string; * c != '\0'; c++) {
        glutBitmapCharacter(GLUT_BITMAP_9_BY_15, * c);
    }
}


double vp_width = 512.0; // update by reshape
double vp_height = 512.0; // update by reshape


void frontscreen(void)
{
    glDisable(GL_LIGHTING);
    glMatrixMode( GL_PROJECTION );
    glPushMatrix();
    glLoadIdentity();
    glOrtho( 0, vp_width, vp_height, 0.0, -1.0, 1.0 );
    glMatrixMode( GL_MODELVIEW );
    glPushMatrix();
    glLoadIdentity();
    glColor3f(0.7,0.0,1.0);
    drawString1(200.0,50.0,0.0,"MVJ College of Engineering");
    glColor3f(0.7,0.0,1.0);
    drawString1(165.0,90.0,0.0,"DEPARTMENT OF COMPUTER SCIENCE AND ENGINEERING");
    glColor3f(1.0,0.5,0.6);
    drawString1(185.0,130.0,0.0,"A MINI PROJECT ON:COMPUTER GRAPHICS");
    glColor3f(1,0,0);
    drawString1(175.0,170.0,0.0,"PROJECT TITLE:CONSTRUCTIVE SOLID GEOMETRY");
    glColor3f(1,0.5,0);
    drawString1(20,380,0.0,"BY:");
    glColor3f(0.5,0,0.5);
    drawString1(10,410,0.0,"NAME: ANSHU");
    glColor3f(0.5,0,0.5);
    drawString1(10,425,0.0,"USN:1MJ15CS016");
    glColor3f(0.5,0,0.5);
    drawString1(10,440,0.0,"SEC:A");
    glColor3f(0.5,0,0.5);
    drawString1(10,455,0.0,"SEMESTER:VI");
    glColor3f(1,0.5,0);
    drawString1(420,380,0.0,"GUIDE:");
    glColor3f(0.5,0,0.5);
    drawString1(390,400,0.0,"NAME:Ms. Devisivashankari p");
    glColor3f(1,0.1,1);
    drawString1(200,480,0.0,"PRESS ENTER TO START");
    glMatrixMode( GL_PROJECTION );
    glPopMatrix();
    glMatrixMode( GL_MODELVIEW );
    glPopMatrix();

    glutSwapBuffers();   // <----- glutSwapBuffers insted of glFlush
    glutPostRedisplay();
}


void mydisplay() {
    glClear(GL_COLOR_BUFFER_BIT|GL_DEPTH_BUFFER_BIT);

    if (isMainScreen) {
        frontscreen();  
    } else {
        redraw();
    }
}


int main(int argc, char **argv)
{
  static GLfloat lightpos[] =
  {25.f, 50.f, -50.f, 1.f};
  static GLfloat sphere_mat[] =
  {1.f, .5f, 0.f, 1.f};
  static GLfloat cone_mat[] =
  {0.f, .5f, 1.f, 1.f};
  GLUquadricObj *sphere, *cone, *base;

  glutInit(&argc, argv);
  glutInitWindowSize(1024,720);
  glutInitDisplayMode(GLUT_STENCIL | GLUT_DEPTH | GLUT_DOUBLE);
  (void) glutCreateWindow("csg");
  glutDisplayFunc(frontscreen);
  glutKeyboardFunc(key);
  glutSpecialFunc(special);
  glutMouseFunc(mouse);
  glutMotionFunc(motion);

  glutCreateMenu(menu);
  glutAddMenuEntry("A only", CSG_A);
  glutAddMenuEntry("B only", CSG_B);
  glutAddMenuEntry("A or B", CSG_A_OR_B);
  glutAddMenuEntry("A and B", CSG_A_AND_B);
  glutAddMenuEntry("A sub B", CSG_A_SUB_B);
  glutAddMenuEntry("B sub A", CSG_B_SUB_A);
  glutAttachMenu(GLUT_RIGHT_BUTTON);

  glEnable(GL_CULL_FACE);
  glEnable(GL_LIGHTING);
  glEnable(GL_LIGHT0);

  glLightfv(GL_LIGHT0, GL_POSITION, lightpos);
  glLightModeli(GL_LIGHT_MODEL_TWO_SIDE, GL_TRUE);

  /* make display lists for sphere and cone; for efficiency */

  glNewList(SPHERE, GL_COMPILE);
  sphere = gluNewQuadric();
  glMaterialfv(GL_FRONT_AND_BACK,GL_AMBIENT_AND_DIFFUSE,sphere_mat);
  gluSphere(sphere, 20.f, 64, 64);
  gluDeleteQuadric(sphere);
  glEndList();
  glNewList(CONE, GL_COMPILE);
  cone = gluNewQuadric();
  base = gluNewQuadric();
  glMaterialfv(GL_FRONT_AND_BACK, GL_AMBIENT_AND_DIFFUSE, cone_mat);
  gluQuadricOrientation(base, GLU_INSIDE);
  gluDisk(base, 0., 15., 64, 1);
  gluCylinder(cone, 15., 0., 60., 64, 64);
  gluDeleteQuadric(cone);
  gluDeleteQuadric(base);
  glEndList();
  glMatrixMode(GL_PROJECTION);
  glOrtho(-50., 50., -50., 50., -50., 50.);
  glMatrixMode(GL_MODELVIEW);
  glutMainLoop();
  return 0;             /* ANSI C requires main to return int. */
}

frontscreen 方法是应该出现的第一个屏幕。

Answer 1

i am able to print text on my first screen,but as the background is black in color and text should come in different colors but it's coming in black color only so it's not visible

启用光照 ( GL_LIGHTING ) 时，颜色将从 Material 参数 ( glMaterial ) 中获取。

如果您仍想使用当前颜色，则必须启用 GL_COLOR_MATERIAL 并设置颜色 Material 参数(glColorMaterial):

glEnable( GL_COLOR_MATERIAL );
glColorMaterial( GL_FRONT_AND_BACK, GL_AMBIENT_AND_DIFFUSE );

另请参阅Basic OpenGL Lighting .

<小时/>

我建议在绘制文本时禁用照明:

void frontscreen(void)
{
    glDisable( GL_LIGHTING );

    .....
}

但是要在绘制场景时启用照明:

void redraw(void)
{
    glEnable( GL_LIGHTING );

    .....
}