一.定位(glRasterPos)

假设你画下一个像素点,那么首先则需要确定位置

二.定义位图的像素点

一个图形由一组像素组成,如下图的F

其像素点由一个数组组成,每行都是一个矩形,如0xc0转成二进制则是11,所以0xc0跟0x00就是从0开始到右侧第2个位置,每行类似.由此这个F的高度为12,宽度为10.

如ff的转换

定义的像素点如下

GLubyte rasters[24] = {
   0xc0, 0x00, 0xc0, 0x00, 0xc0, 0x00, 0xc0, 0x00, 0xc0, 0x00,
   0xff, 0x00, 0xff, 0x00, 0xc0, 0x00, 0xc0, 0x00, 0xc0, 0x00,
   0xff, 0xc0, 0xff, 0xc0};

绘制像素点

我们知道正常图片不管放大还是缩小都会变的模糊,为了保持最清晰状态,那么展示的图片跟大小就要跟源高度宽度相符合,所以上面的F高度宽度为12,10

使用glBitmap绘制绘图

glBitmap (10, 12, 0.0, 0.0, 11.0, 0.0, rasters);

第1,2个参数表示宽度与高度

当指定glRasterPos参数时，其坐标点则作为原始的(0,0)坐标点

第3,4个参数表示与相对坐标的位置

绘制多个位图

当一个位图位置完毕后,如果位图没有完成，则继续绘制像素点,当一个位图绘制完成后,可以进行移位,移位后的坐标则成为了起始点，
如上glBitmap的第5,6个参数,表示位移几个像素,由于宽度是10,所以要大于10才不会导致位图重叠,我们将x坐标的间隔改为25,绘制三个F看一下效果,如下

下图解释了glBitmap参数的用法

示例代码

GLubyte rasters[24] = {
   0xc0, 0x00, 0xc0, 0x00, 0xc0, 0x00, 0xc0, 0x00, 0xc0, 0x00,
   0xff, 0x00, 0xff, 0x00, 0xc0, 0x00, 0xc0, 0x00, 0xc0, 0x00,
   0xff, 0xc0, 0xff, 0xc0};

void init(void)
{
   glPixelStorei (GL_UNPACK_ALIGNMENT, 1);
   glClearColor (0.0, 0.0, 0.0, 0.0);
}

void display(void)
{
   glClear(GL_COLOR_BUFFER_BIT);
   glColor3f (1.0, 1.0, 1.0);
   glRasterPos2i (20, 20);
   glBitmap (10, 12, 0.0, 0.0, 25.0, 0.0, rasters);
   glBitmap (10, 12, 0.0, 0.0, 25.0, 0.0, rasters);
   glBitmap (10, 12, 0.0, 0.0, 25.0, 0.0, rasters);
   glFlush();
  
}

记得先初始化时调用glPixelStorei (GL_UNPACK_ALIGNMENT, 1);

绘制完整的英文字母

首先需要把26个英文字母的像素点给绘制下来,然后保存到各自的显示列表中,并记录显示列表的索引值,然后根据输入的文字,调用相关的显示列表索引值

先看效果

代码示例,像素点真的很晕…

GLubyte space[] = 
{0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00};

GLubyte letters[][13] = {
{0x00, 0x00, 0xc3, 0xc3, 0xc3, 0xc3, 0xff, 0xc3, 0xc3, 0xc3, 0x66, 0x3c, 0x18}, 
{0x00, 0x00, 0xfe, 0xc7, 0xc3, 0xc3, 0xc7, 0xfe, 0xc7, 0xc3, 0xc3, 0xc7, 0xfe}, 
{0x00, 0x00, 0x7e, 0xe7, 0xc0, 0xc0, 0xc0, 0xc0, 0xc0, 0xc0, 0xc0, 0xe7, 0x7e}, 
{0x00, 0x00, 0xfc, 0xce, 0xc7, 0xc3, 0xc3, 0xc3, 0xc3, 0xc3, 0xc7, 0xce, 0xfc}, 
{0x00, 0x00, 0xff, 0xc0, 0xc0, 0xc0, 0xc0, 0xfc, 0xc0, 0xc0, 0xc0, 0xc0, 0xff}, 
{0x00, 0x00, 0xc0, 0xc0, 0xc0, 0xc0, 0xc0, 0xc0, 0xfc, 0xc0, 0xc0, 0xc0, 0xff}, 
{0x00, 0x00, 0x7e, 0xe7, 0xc3, 0xc3, 0xcf, 0xc0, 0xc0, 0xc0, 0xc0, 0xe7, 0x7e}, 
{0x00, 0x00, 0xc3, 0xc3, 0xc3, 0xc3, 0xc3, 0xff, 0xc3, 0xc3, 0xc3, 0xc3, 0xc3}, 
{0x00, 0x00, 0x7e, 0x18, 0x18, 0x18, 0x18, 0x18, 0x18, 0x18, 0x18, 0x18, 0x7e}, 
{0x00, 0x00, 0x7c, 0xee, 0xc6, 0x06, 0x06, 0x06, 0x06, 0x06, 0x06, 0x06, 0x06}, 
{0x00, 0x00, 0xc3, 0xc6, 0xcc, 0xd8, 0xf0, 0xe0, 0xf0, 0xd8, 0xcc, 0xc6, 0xc3}, 
{0x00, 0x00, 0xff, 0xc0, 0xc0, 0xc0, 0xc0, 0xc0, 0xc0, 0xc0, 0xc0, 0xc0, 0xc0}, 
{0x00, 0x00, 0xc3, 0xc3, 0xc3, 0xc3, 0xc3, 0xc3, 0xdb, 0xff, 0xff, 0xe7, 0xc3}, 
{0x00, 0x00, 0xc7, 0xc7, 0xcf, 0xcf, 0xdf, 0xdb, 0xfb, 0xf3, 0xf3, 0xe3, 0xe3}, 
{0x00, 0x00, 0x7e, 0xe7, 0xc3, 0xc3, 0xc3, 0xc3, 0xc3, 0xc3, 0xc3, 0xe7, 0x7e}, 
{0x00, 0x00, 0xc0, 0xc0, 0xc0, 0xc0, 0xc0, 0xfe, 0xc7, 0xc3, 0xc3, 0xc7, 0xfe}, 
{0x00, 0x00, 0x3f, 0x6e, 0xdf, 0xdb, 0xc3, 0xc3, 0xc3, 0xc3, 0xc3, 0x66, 0x3c}, 
{0x00, 0x00, 0xc3, 0xc6, 0xcc, 0xd8, 0xf0, 0xfe, 0xc7, 0xc3, 0xc3, 0xc7, 0xfe}, 
{0x00, 0x00, 0x7e, 0xe7, 0x03, 0x03, 0x07, 0x7e, 0xe0, 0xc0, 0xc0, 0xe7, 0x7e}, 
{0x00, 0x00, 0x18, 0x18, 0x18, 0x18, 0x18, 0x18, 0x18, 0x18, 0x18, 0x18, 0xff}, 
{0x00, 0x00, 0x7e, 0xe7, 0xc3, 0xc3, 0xc3, 0xc3, 0xc3, 0xc3, 0xc3, 0xc3, 0xc3}, 
{0x00, 0x00, 0x18, 0x3c, 0x3c, 0x66, 0x66, 0xc3, 0xc3, 0xc3, 0xc3, 0xc3, 0xc3}, 
{0x00, 0x00, 0xc3, 0xe7, 0xff, 0xff, 0xdb, 0xdb, 0xc3, 0xc3, 0xc3, 0xc3, 0xc3}, 
{0x00, 0x00, 0xc3, 0x66, 0x66, 0x3c, 0x3c, 0x18, 0x3c, 0x3c, 0x66, 0x66, 0xc3}, 
{0x00, 0x00, 0x18, 0x18, 0x18, 0x18, 0x18, 0x18, 0x3c, 0x3c, 0x66, 0x66, 0xc3}, 
{0x00, 0x00, 0xff, 0xc0, 0xc0, 0x60, 0x30, 0x7e, 0x0c, 0x06, 0x03, 0x03, 0xff}
};

GLuint fontOffset;

void makeRasterFont(void)
{
   GLuint i, j;
   glPixelStorei(GL_UNPACK_ALIGNMENT, 1);

   fontOffset = glGenLists (128);
   for (i = 0,j = 'A'; i < 26; i++,j++) {
      glNewList(fontOffset + j, GL_COMPILE);
      glBitmap(8, 13, 0.0, 2.0, 10.0, 0.0, letters[i]);
      glEndList();
   }
   glNewList(fontOffset + ' ', GL_COMPILE);
   glBitmap(8, 13, 0.0, 2.0, 10.0, 0.0, space);
   glEndList();
}

void init(void)
{
   glShadeModel (GL_FLAT);
   makeRasterFont();
}

void printString(char *s)
{
   glPushAttrib (GL_LIST_BIT);
   glListBase(fontOffset);
   glCallLists(strlen(s), GL_UNSIGNED_BYTE, (GLubyte *) s);
   glPopAttrib ();
}

/* Everything above this line could be in a library 
 * that defines a font.  To make it work, you've got 
 * to call makeRasterFont() before you start making 
 * calls to printString().
 */
void display(void)
{
   GLfloat white[3] = { 1.0, 1.0, 1.0 };

   glClear(GL_COLOR_BUFFER_BIT);
   glColor3fv(white);

   glRasterPos2i(20, 60);
   printString("THE QUICK BROWN FOX JUMPS");
   glRasterPos2i(20, 40);
   printString("OVER A LAZY DOG");
   glFlush ();
}