Drawing a Bitmapped Character or string in OpenGL sample example

A bitmap is a rectangular array of 0s and 1s that serves as a drawing mask for a corresponding rectangular portion of the window. Suppose you're drawing a bitmap and that the current raster color is red. Wherever there's a 1 in the bitmap, the corresponding pixel is replaced by a red pixel and If there's a 0 in the bitmap, the contents of thepixel are unaffected. The most common use of bitmaps is for drawing characters on the screen.

            In the simple example we use two main function glBitmap and glRasterPos2i function.

The glBitmap function draws a bitmap.

Syntax

void WINAPI glBitmap(
GLSizei width,

GLfloat xorig,
GLSizei height
,
GLfloat yorig,
float ymove,
c
GLfloat xmove,
G
Lonst GLubyte *bitmap
);

Parameters

width

The pixel width of the bitmap image.

height

The pixel height of the bitmap image.

xorig

The x location of the origin in the bitmap image. The origin is measured from the lower-left corner of the bitmap, with right and up directions being the positive axes.

yorig

The y location of the origin in the bitmap image. The origin is measured from the lower-left corner of the bitmap, with right and up directions being the positive axes.

xmove

The x offset to be added to the current raster position after the bitmap is drawn.

ymove

The y offset to be added to the current raster position after the bitmap is drawn.

bitmap

The address of the bitmap image.

        A bitmap is a binary image. When drawn, the bitmap is positioned relative to the current raster position, and framebuffer pixels corresponding to 1s in the bitmap are written using the current raster color or index. Frame-buffer pixels corresponding to zeros in the bitmap are not modified.If the current raster position is invalid, glBitmap is ignored.

The glRasterPos2i function specifies  the raster position for pixel operations like glBitmap function.

Syntax

void WINAPI glRasterPos2i(
GLint x,
GLint y
);

Parameters

x

Specifies the x-coordinate for the current raster position.

y

Specifies the y-coordinate for the current raster position.

         In this program glBitmap function draw the single bitmap or character in the screen and glRasterPos2i is specifies the position of character.To draw the string the displaylist mechanism is used to draw a sequence of character.The value of bitmap is store in GLubyte array.GLubyte Array[] store the pixel value and this value is used to draw the pixel of  13 rows/heightand  8 colum/width Drawing pixel is started form bottom rows.We will provide the hexadecimal number 00 to ff for 8 pixelif pixel value is 1 then it is replace by white color if value is 0 then it is unaffected.For example,for drawing dot at array GLubyte dot[2] data is provided 0x18.Here 18 is hexadecimal value converting it into decimal value we get 00011000 so 4th and 5th pixel of bottom row is replace by white color and other is unaffected like this all the character is drawn.

Here is the sample source code ,copy and compile it in codeblocks.

#include <windows.h>

#include <GL/glut.h>

#include <stdlib.h>

#include <string.h>

/*

Here GLubyte Array[] store the pixel value and this value is used to draw the pixel of  13 rows/height

and  8 colum/width Drawing pixel is started form bottom rows.

We will provide the hexadecimal number 00 to ff for 8 pixel

if pixel value is 1 then it is replace by white color if value is 0 then it is unaffected.

For example,for drawing dot at array GLubyte dot[2] data is provided 0x18.Here 18 is hexadecimal value

converting it into decimal value we get 00011000 so 4th and 5th pixel of bottom row is replace by white

color and other is unaffected like this all the character is drawn.

*/

GLubyte space[] =

{0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00};//for spacebar,draw nothing

GLubyte dot[] =

{0x00, 0x00, 0x18, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00};//draw dot

GLubyte letters[][13] = {

{0x00, 0x00, 0xc3, 0xc3, 0xc3, 0xc3, 0xff, 0xc3, 0xc3, 0xc3, 0x66, 0x3c, 0x18},//draw A

{0x00, 0x00, 0xfe, 0xc7, 0xc3, 0xc3, 0xc7, 0xfe, 0xc7, 0xc3, 0xc3, 0xc7, 0xfe},//draw B

{0x00, 0x00, 0x7e, 0xe7, 0xc0, 0xc0, 0xc0, 0xc0, 0xc0, 0xc0, 0xc0, 0xe7, 0x7e},//draw C

{0x00, 0x00, 0xfc, 0xce, 0xc7, 0xc3, 0xc3, 0xc3, 0xc3, 0xc3, 0xc7, 0xce, 0xfc},//draw D

{0x00, 0x00, 0xff, 0xc0, 0xc0, 0xc0, 0xc0, 0xfc, 0xc0, 0xc0, 0xc0, 0xc0, 0xff},//draw E

{0x00, 0x00, 0xc0, 0xc0, 0xc0, 0xc0, 0xc0, 0xc0, 0xfc, 0xc0, 0xc0, 0xc0, 0xff},//draw F

{0x00, 0x00, 0x7e, 0xe7, 0xc3, 0xc3, 0xcf, 0xc0, 0xc0, 0xc0, 0xc0, 0xe7, 0x7e},//draw G

{0x00, 0x00, 0xc3, 0xc3, 0xc3, 0xc3, 0xc3, 0xff, 0xc3, 0xc3, 0xc3, 0xc3, 0xc3},//draw H

{0x00, 0x00, 0x7e, 0x18, 0x18, 0x18, 0x18, 0x18, 0x18, 0x18, 0x18, 0x18, 0x7e},//draw I

{0x00, 0x00, 0x7c, 0xee, 0xc6, 0x06, 0x06, 0x06, 0x06, 0x06, 0x06, 0x06, 0x06},//draw J

{0x00, 0x00, 0xc3, 0xc6, 0xcc, 0xd8, 0xf0, 0xe0, 0xf0, 0xd8, 0xcc, 0xc6, 0xc3},//draw K

{0x00, 0x00, 0xff, 0xc0, 0xc0, 0xc0, 0xc0, 0xc0, 0xc0, 0xc0, 0xc0, 0xc0, 0xc0},//draw L

{0x00, 0x00, 0xc3, 0xc3, 0xc3, 0xc3, 0xc3, 0xc3, 0xdb, 0xff, 0xff, 0xe7, 0xc3},//draw M

{0x00, 0x00, 0xc7, 0xc7, 0xcf, 0xcf, 0xdf, 0xdb, 0xfb, 0xf3, 0xf3, 0xe3, 0xe3},//draw N

{0x00, 0x00, 0x7e, 0xe7, 0xc3, 0xc3, 0xc3, 0xc3, 0xc3, 0xc3, 0xc3, 0xe7, 0x7e},//draw O

{0x00, 0x00, 0xc0, 0xc0, 0xc0, 0xc0, 0xc0, 0xfe, 0xc7, 0xc3, 0xc3, 0xc7, 0xfe},//draw P

{0x00, 0x00, 0x3f, 0x6e, 0xdf, 0xdb, 0xc3, 0xc3, 0xc3, 0xc3, 0xc3, 0x66, 0x3c},//draw Q

{0x00, 0x00, 0xc3, 0xc6, 0xcc, 0xd8, 0xf0, 0xfe, 0xc7, 0xc3, 0xc3, 0xc7, 0xfe},//draw R

{0x00, 0x00, 0x7e, 0xe7, 0x03, 0x03, 0x07, 0x7e, 0xe0, 0xc0, 0xc0, 0xe7, 0x7e},//draw S

{0x00, 0x00, 0x18, 0x18, 0x18, 0x18, 0x18, 0x18, 0x18, 0x18, 0x18, 0x18, 0xff},//draw T

{0x00, 0x00, 0x7e, 0xe7, 0xc3, 0xc3, 0xc3, 0xc3, 0xc3, 0xc3, 0xc3, 0xc3, 0xc3},//draw U

{0x00, 0x00, 0x18, 0x3c, 0x3c, 0x66, 0x66, 0xc3, 0xc3, 0xc3, 0xc3, 0xc3, 0xc3},//draw V

{0x00, 0x00, 0xc3, 0xe7, 0xff, 0xff, 0xdb, 0xdb, 0xc3, 0xc3, 0xc3, 0xc3, 0xc3},//draw W

{0x00, 0x00, 0xc3, 0x66, 0x66, 0x3c, 0x3c, 0x18, 0x3c, 0x3c, 0x66, 0x66, 0xc3},//draw X

{0x00, 0x00, 0x18, 0x18, 0x18, 0x18, 0x18, 0x18, 0x3c, 0x3c, 0x66, 0x66, 0xc3},//draw Y

{0x00, 0x00, 0xff, 0xc0, 0xc0, 0x60, 0x30, 0x7e, 0x0c, 0x06, 0x03, 0x03, 0xff} //draw Z

};

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();

glNewList(fontOffset + '.', GL_COMPILE);

glBitmap(8, 13, 0.0, 2.0, 10.0, 0.0, dot);

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 ();

}

void display(void)

{

GLfloat white[3] = { 1.0, 1.0, 1.0 };

glClear(GL_COLOR_BUFFER_BIT);

glColor3fv(white);

glRasterPos2i(245, 320);

printString("WELCOME TO THE");

glRasterPos2i(180, 300);

printString("WWW.CODEINCODEBLOCK.BLOGSPOT.COM");

glRasterPos2i(230,280);

printString("PRESS ESC TO EXIT");

glFlush ();

}

void reshape(int w, int h)

{

glViewport(0, 0, (GLsizei) w, (GLsizei) h);

glMatrixMode(GL_PROJECTION);

glLoadIdentity();

glOrtho (0.0, w, 0.0, h, -1.0, 1.0);

glMatrixMode(GL_MODELVIEW);

}

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

{

switch (key) {

case 27:

exit(0);

}

}

int main(int argc, char** argv)

{

glutInit(&argc, argv);

glutInitDisplayMode(GLUT_SINGLE | GLUT_RGB);

glutInitWindowSize(600, 600);

glutInitWindowPosition (100,100);

glutCreateWindow(argv[0]);

init();

glutReshapeFunc(reshape);

glutKeyboardFunc(keyboard);

glutDisplayFunc(display);

glutMainLoop();

return 0;

}