博客转自：http://www.lighthouse3d.com/tutorials/glut-tutorial/bitmap-fonts/

位图字体是一个2维的字体，虽然我们会将它放置在3维的世界内，但是这些字体没有厚度，不可以被旋转或者缩放；只可以被平移。而且，这种字体永远只朝向观测者的视野，就像看着宣传板一样。尽管这些特性是潜在的劣势，但是从另外一方面来看，我们不需要关心如何设置他的朝向使其朝向观测者的视野。

在这个小节，我们将呈现 GLUT 如何将位图字体显示在屏幕上。我们需要使用函数 glutBitmapCharacter 去写一个字符。

void glutBitmapCharacter(void *font, int character)

Parameters:

font – the name of the font to use (see bellow for a list of what’s available
character – what to render, a letter, symbol, number, etc…

The font options available are:

• GLUT_BITMAP_8_BY_13
• GLUT_BITMAP_9_BY_15
• GLUT_BITMAP_TIMES_ROMAN_10
• GLUT_BITMAP_TIMES_ROMAN_24
• GLUT_BITMAP_HELVETICA_10
• GLUT_BITMAP_HELVETICA_12
• GLUT_BITMAP_HELVETICA_18

想要观测各种字体的显示效果，可以尝试将所有字体类型都显示在弹出菜单中。下面的函数输出一个字符到当前光栅位置。

glutBitmapCharacter(GLUT_BITMAP_HELVETICA_18,'3');

 需要解释一下光栅位置，我们可以通过函数OpenGL库中的 glRasterPos 函数设置光栅位置。

void glRasterPos2f(float x, float y);
void glRasterPos3f(float x, float y, float z);

Parameters:

x, y, z – local coordinates for the text to appear

函数 glutBitmapCharacter 依据字符的宽度在指定位置渲染字符。因此，如果想渲染字符串，需要连续调用 glutBitmapCharacter 函数，将会得到想要的显示效果。下面是渲染字符串的例子

void renderBitmapString(
        float x,
        float y,
        float z,
        void *font,
        char *string) {

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

完整代码如下

#include <stdlib.h>
#include <stdio.h>
#include <math.h>

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

// angle of rotation for the camera direction
float angle = 0.0f;

// actual vector representing the camera's direction
float lx = 0.0f, lz = -1.0f;

// XZ position of the camera
float x = 0.0f, z = 5.0f;

// the key states. These variables will be zero
//when no key is being presses
float deltaAngle = 0.0f;
float deltaMove = 0;
int xOrigin = -1;

// Constant definitions for Menus
#define RED 1
#define GREEN 2
#define BLUE 3
#define ORANGE 4

#define FILL 1
#define LINE 2

// Pop up menu identifiers
int fillMenu, fontMenu, mainMenu, colorMenu;

// color for the nose
float red = 1.0f, blue = 0.5f, green = 0.5f;

// scale of snowman
float scale = 1.0f;

// menu status
int menuFlag = 0;

// default font
void *font = GLUT_BITMAP_TIMES_ROMAN_24;

#define INT_GLUT_BITMAP_8_BY_13 1
#define INT_GLUT_BITMAP_9_BY_15 2
#define INT_GLUT_BITMAP_TIMES_ROMAN_10  3
#define INT_GLUT_BITMAP_TIMES_ROMAN_24  4
#define INT_GLUT_BITMAP_HELVETICA_10  5
#define INT_GLUT_BITMAP_HELVETICA_12  6
#define INT_GLUT_BITMAP_HELVETICA_18  7

void changeSize(int w, int h) {

    // Prevent a divide by zero, when window is too short
    // (you cant make a window of zero width).
    if (h == 0)
        h = 1;

    float ratio = w * 1.0 / h;

    // Use the Projection Matrix
    glMatrixMode(GL_PROJECTION);

    // Reset Matrix
    glLoadIdentity();

    // Set the viewport to be the entire window
    glViewport(0, 0, w, h);

    // Set the correct perspective.
    gluPerspective(45.0f, ratio, 0.1f, 100.0f);

    // Get Back to the Modelview
    glMatrixMode(GL_MODELVIEW);
}

void drawSnowMan() {

    glScalef(scale, scale, scale);
    glColor3f(1.0f, 1.0f, 1.0f);

    // Draw Body
    glTranslatef(0.0f, 0.75f, 0.0f);
    glutSolidSphere(0.75f, 20, 20);

    // Draw Head
    glTranslatef(0.0f, 1.0f, 0.0f);
    glutSolidSphere(0.25f, 20, 20);

    // Draw Eyes
    glPushMatrix();
    glColor3f(0.0f, 0.0f, 0.0f);
    glTranslatef(0.05f, 0.10f, 0.18f);
    glutSolidSphere(0.05f, 10, 10);
    glTranslatef(-0.1f, 0.0f, 0.0f);
    glutSolidSphere(0.05f, 10, 10);
    glPopMatrix();

    // Draw Nose
    glColor3f(red, green, blue);
    glRotatef(0.0f, 1.0f, 0.0f, 0.0f);
    glutSolidCone(0.08f, 0.5f, 10, 2);

    glColor3f(1.0f, 1.0f, 1.0f);

}

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

void computePos(float deltaMove) {

    x += deltaMove * lx * 0.1f;
    z += deltaMove * lz * 0.1f;
}

void renderScene(void)
{
    if (deltaMove)
        computePos(deltaMove);

    // Clear Color and Depth Buffers
    glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);

    // Reset transformations
    glLoadIdentity();
    
    // Set the camera
    gluLookAt(x, 1.0f, z,
        x + lx, 1.0f, z + lz,
        0.0f, 1.0f, 0.0f);

    // Draw ground
    glColor3f(0.9f, 0.9f, 0.9f);
    glBegin(GL_QUADS);
    glVertex3f(-100.0f, 0.0f, -100.0f);
    glVertex3f(-100.0f, 0.0f, 100.0f);
    glVertex3f(100.0f, 0.0f, 100.0f);
    glVertex3f(100.0f, 0.0f, -100.0f);
    glEnd();

    // Draw 36 SnowMen
    char number[3];
    for (int i = -3; i < 3; i++)
    {
        for (int j = -3; j < 3; j++)
        {
            glPushMatrix();
            glTranslatef(i*10.0f, 0.0f, j * 10.0f);
            drawSnowMan();
            sprintf(number, "%d", (i + 3) * 6 + (j + 3));
            renderBitmapString(0.0f, 0.5f, 0.0f, (void *)font, number);
            glPopMatrix();
        }
    }
        
    glutSwapBuffers();
}

// -----------------------------------
//             KEYBOARD
// -----------------------------------

void processNormalKeys(unsigned char key, int xx, int yy)
{
    switch (key) 
    {
    case 27:
        glutDestroyMenu(mainMenu);
        glutDestroyMenu(fillMenu);
        glutDestroyMenu(colorMenu);
        glutDestroyMenu(fontMenu);
        exit(0);
        break;
    }
}

void pressKey(int key, int xx, int yy)
{
    switch (key) 
    {
    case GLUT_KEY_UP: deltaMove = 0.5f; break;
    case GLUT_KEY_DOWN: deltaMove = -0.5f; break;
    }
}

void releaseKey(int key, int x, int y)
{
    switch (key) 
    {
    case GLUT_KEY_UP:
    case GLUT_KEY_DOWN: deltaMove = 0; break;
    }
}

// -----------------------------------
//             MOUSE
// -----------------------------------

void mouseMove(int x, int y)
{
    // this will only be true when the left button is down
    if (xOrigin >= 0) 
    {
        // update deltaAngle
        deltaAngle = (x - xOrigin) * 0.001f;

        // update camera's direction
        lx = sin(angle + deltaAngle);
        lz = -cos(angle + deltaAngle);
    }
}

void mouseButton(int button, int state, int x, int y) 
{
    // only start motion if the left button is pressed
    if (button == GLUT_LEFT_BUTTON) {

        // when the button is released
        if (state == GLUT_UP) {
            angle += deltaAngle;
            xOrigin = -1;
        }
        else  {// state = GLUT_DOWN
            xOrigin = x;
        }
    }
}

// -----------------------------------
//             MENUS
// -----------------------------------

void processMenuStatus(int status, int x, int y) 
{
    if (status == GLUT_MENU_IN_USE)
        menuFlag = 1;
    else
        menuFlag = 0;
}

void processMainMenu(int option)
{
    // nothing to do in here
    // all actions are for submenus
}

void processFillMenu(int option) 
{
    switch (option) 
    {
    case FILL: glPolygonMode(GL_FRONT, GL_FILL); break;
    case LINE: glPolygonMode(GL_FRONT, GL_LINE); break;
    }
}

void processFontMenu(int option)
{
    switch (option)
    {
    case INT_GLUT_BITMAP_8_BY_13:
        font = GLUT_BITMAP_8_BY_13;
        break;
    case INT_GLUT_BITMAP_9_BY_15:
        font = GLUT_BITMAP_9_BY_15;
        break;
    case INT_GLUT_BITMAP_TIMES_ROMAN_10:
        font = GLUT_BITMAP_TIMES_ROMAN_10;
        break;
    case INT_GLUT_BITMAP_TIMES_ROMAN_24:
        font = GLUT_BITMAP_TIMES_ROMAN_24;
        break;
    case INT_GLUT_BITMAP_HELVETICA_10:
        font = GLUT_BITMAP_HELVETICA_10;
        break;
    case INT_GLUT_BITMAP_HELVETICA_12:
        font = GLUT_BITMAP_HELVETICA_12;
        break;
    case INT_GLUT_BITMAP_HELVETICA_18:
        font = GLUT_BITMAP_HELVETICA_18;
        break;
    }
}

void processColorMenu(int option)
{
    switch (option) {
    case RED:
        red = 1.0f;
        green = 0.0f;
        blue = 0.0f; break;
    case GREEN:
        red = 0.0f;
        green = 1.0f;
        blue = 0.0f; break;
    case BLUE:
        red = 0.0f;
        green = 0.0f;
        blue = 1.0f; break;
    case ORANGE:
        red = 1.0f;
        green = 0.5f;
        blue = 0.5f; break;
    }
}

void createPopupMenus() 
{
    fontMenu = glutCreateMenu(processFontMenu);

    glutAddMenuEntry("BITMAP_8_BY_13 ", INT_GLUT_BITMAP_8_BY_13);
    glutAddMenuEntry("BITMAP_9_BY_15", INT_GLUT_BITMAP_9_BY_15);
    glutAddMenuEntry("BITMAP_TIMES_ROMAN_10 ", INT_GLUT_BITMAP_TIMES_ROMAN_10);
    glutAddMenuEntry("BITMAP_TIMES_ROMAN_24", INT_GLUT_BITMAP_TIMES_ROMAN_24);
    glutAddMenuEntry("BITMAP_HELVETICA_10 ", INT_GLUT_BITMAP_HELVETICA_10);
    glutAddMenuEntry("BITMAP_HELVETICA_12", INT_GLUT_BITMAP_HELVETICA_12);
    glutAddMenuEntry("BITMAP_HELVETICA_18", INT_GLUT_BITMAP_HELVETICA_18);

    fillMenu = glutCreateMenu(processFillMenu);

    glutAddMenuEntry("Fill", FILL);
    glutAddMenuEntry("Line", LINE);

    colorMenu = glutCreateMenu(processColorMenu);
    glutAddMenuEntry("Red", RED);
    glutAddMenuEntry("Blue", BLUE);
    glutAddMenuEntry("Green", GREEN);
    glutAddMenuEntry("Orange", ORANGE);

    mainMenu = glutCreateMenu(processMainMenu);

    glutAddSubMenu("Polygon Mode", fillMenu);
    glutAddSubMenu("Color", colorMenu);
    glutAddSubMenu("Font", fontMenu);
    // attach the menu to the right button
    glutAttachMenu(GLUT_RIGHT_BUTTON);

    // this will allow us to know if the menu is active
    glutMenuStatusFunc(processMenuStatus);
}

// -----------------------------------
//             MAIN
// -----------------------------------

int main(int argc, char **argv)
{
    glutInit(&argc, argv);
    glutInitDisplayMode(GLUT_DEPTH | GLUT_DOUBLE | GLUT_RGBA);
    glutInitWindowPosition(100, 100);
    glutInitWindowSize(320, 320);
    glutCreateWindow("Lighthouse3D - GLUT Tutorial");

    // register callbacks
    glutDisplayFunc(renderScene);
    glutReshapeFunc(changeSize);
    glutIdleFunc(renderScene);

    glutIgnoreKeyRepeat(1);
    glutKeyboardFunc(processNormalKeys);
    glutSpecialFunc(pressKey);
    glutSpecialUpFunc(releaseKey);

    // here are the two new functions
    glutMouseFunc(mouseButton);
    glutMotionFunc(mouseMove);

    // OpenGL init
    glEnable(GL_DEPTH_TEST);
    glEnable(GL_CULL_FACE);

    // init Menus
    createPopupMenus();

    // enter GLUT event processing cycle
    glutMainLoop();

    return 1;
}

显示效果如下