CS0045 Module 3

These functions are essential for rendering bitmap or stroke-based text in OpenGL, particularly when using the GLUT toolkit

Text & Raster Positioning Function

They operate within the rasterization stage of the graphics pipeline, where pixel-based operations are performed

Text & Raster Positioning Function

Purpose: Sets the current raster position in 2D space

Text & Raster Positioning Function

Parameters: x, y: Floating-point coordinates in object space

Text & Raster Positioning Function

Usage Context:

• Defines where bitmap text or pixel images will be drawn

• Transformed by the current model view and projection matrices

Text & Raster Positioning Function

Sets the raster position in 2D space for pixel-based operations such as bitmap text or image rendering

glRasterPos2f()

Coordinates are specified in the current model view and projection context

glRasterPos2f()

Renders a string of bitmap characters at the current raster position using a specified GLUT bitmap font

glutBitmapString()

Commonly used for simple on-screen text in legacy OpenGL

glutBitmapString()

drawBitmapString() is an extension of freeglut, therefore you need to add this to your code

#include <GL/glut.h>
#include <GL/freeglut_ext.h>

#include <GL/glut.h>
#include <GL/freeglut_ext.h>

using namespace std;

void textSample(){
    glClear(GL_COLOR_BUFFER_BIT);
    
    const unsigned char str[100] = {"FEU-TECH"};
    glColor3f(1.0f, 1.0f, 1.0f);
    glRasterPos2f(0.0, 0.0);
    glutBitmapString(GLUT_BITMAP_HELVETICA_18, str);

    glFlush();
}

int main(int argc, char** argv){
    glutInit(&argc, argv);
    glutCreateWindow("Line Strip");
    glutDisplayFunc(textSample);

    glutMainLoop();

return 0;
}

Drawing Text (*Note: Set the color before the position)

glColor3f(0.0f, 0.0f, 1.0f);

Blue

glColor3f(1.0f, 0.0f, 0.0f);

Red

glColor3f(0.0f, 1.0f, 0.0f);

Green

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

White

glColor3f(1.0f, 1.0f, 0.0f);

Yellow

glColor3f(1.0f, 0.0f, 1.0f)

Magenta

GLUT_STROKE_ROMAN
GLUT_STROKE_MONO_ROMAN
GLUT_BITMAP_9_BY_15
GLUT_BITMAP_8_BY_13
GLUT_BITMAP_TIMES_ROMAN_10
GLUT_BITMAP_TIMES_ROMAN_24
GLUT_BITMAP_HELVETICA_10
GLUT_BITMAP_HELVETICA_12
GLUT_BITMAP_HELVETICA_18

Available GLUT Font Constants

A GLUT stroke font rendered using line segments, allowing scalable vector-based text. Suitable for zoomable or transformable text in 3D scenes

GLUT_STROKE_ROMAN

A fixed-size bitmap font in Helvetica style with 12-point height. Used for rendering small, readable text in 2D overlays or HUDs

GLUT_BITMAP_HELVETICA_12

Refer to the foundational steps required to create and prepare a graphical window for rendering OpenGL content

Window Initialization & Configuration

This process is typically handled using the GLUT (OpenGL Utility Toolkit), which abstracts platform-specific windowing operations

Window Initialization & Configuration

Key Components:

glutInit()
glutInitWindowSize(int width, int height)
glutInitWindowPosition(int x, int y)
glutCreateWindow(const char *title)

Window Initialization & Configuration

Should only be called once in a GLUT program

glutInit()

Used to initialize the GLUT library

glutInit()

Sets the window size and position respectively

glutInitWindowSize()
glutInitWindowPosition()

Usage:

glutInitWindowSize(int width, int height);
glutInitWindowPosition(int x, int y);

width

Width in pixels

height

Height in pixels

x Window X location in pixels

y Window Y location in pixels

Creates a top-level window

glutCreateWindow()

Usage:

int glutCreateWindow(char *name);

name //ASCII character string for use as window name

glutCreateWindow()

Requests that current window be made full screen

glutFullScreen()

Usage:

void glutFullScreen(void);

glutFullScreen()

Marks the current window as needing to be redisplayed

glutPostRedisplay()

Most of the time used in callbacks

glutPostRedisplay()

Usage:

void glutPostRedisplay(void);

glutPostRedisplay()

Enable interactive graphics applications by capturing and responding to user-generated events such as keyboard presses, mouse movements, and clicks

Input Handling Functions

In GLUT, these functions are registered as callback handlers, allowing the application to define custom behavior for each input type

Input Handling Functions

Sets the display callback for the current window

glutDisplayFunc()

Usage:

void glutDisplayFunc(void (*func) (void));

func //The new display callback function

glutDisplayFunc()

Sets the keyboard callback for the current window

glutKeyboardFunc()

Usage:

void glutKeyboardFunc(void (*func) (unsigned char key, int x, int y));

glutKeyboardFunc()

#include <iostream>
#include <GL/glut.h>
#include <GL/freeglut_ext.h>

using namespace std;

void defaultDisplay();
void keyboardMonitor(unsigned char key, int x, int y);

float px, py;

int main(int argc, char** argv){
    glutInit(&argc, argv);
    glutInitWindowSize(1024, 768);
    glutInitWindowPosition(200,50);

    glutCreateWindow("My First OpenGL");
    //glutFullScreen();
    glutDisplayFunc(defaultDisplay);
    glutKeyboardFunc(keyboardMonitor);

    glutMainLoop();

return 0;
}

void keyboardMonitor(unsigned char key, int x, int y){
    cout << key << endl;
    switch(key) {
        case 'a':
            px -= .02f;
            break;
        case 'd':
            px += .02f;
            break;

        default:
        px=0.0f;
    }
    glutPostRedisplay();
}

void defaultDisplay(){
    glClear(GL_COLOR_BUFFER_BIT);

    const unsigned char str[100] = "Tony Tony Chopper";
    glColor3f(1.0f,0.75f,0.8f);
    glRasterPos2f(px,py);
    glutBitmapString(GLUT_BITMAP_HELVETICA_18, str);


    glFlush();
}

glutKeyboardFunc() Sample Code

Sets the mouse callback for the current window

glutMouseFunc()

Usage:

void glutMouseFunc(void (*func) (int button, int state, int x, int y));

func //The new mouse callback funtion

glutMouseFunc()

When a user presses and releases mouse buttons in the window, each press and each release generates a mouse callback

glutMouseFunc()

The button parameter is one of GLUT LEFT BUTTON, GLUT MIDDLE BUTTON, or GLUT RIGHT BUTTON

glutMouseFunc()

The state parameter is either GLUT UP or GLUT DOWN

glutMouseFunc()

void mouseMonitor(int button, int state, int x, int y) {
    if (button == GLUT_LEFT_BUTTON) {
        if ( state == GLUT_DOWN)
            cout << "Left button was clicked..." << endl;
        else
            cout << "Left button was released..." << endl;
    } else if(button == GLUT_RIGHT_BUTTON){
        cout << "Right button was clicked..." << endl;
    } else {
        cout << "Middle button was clicked..." << endl;
    }
    cout << x << " " << y << endl;
    //cout << button << endl;
}

glutMouseFunc()

The passive motion callback for a window is called when the mouse moves within the window while no mouse buttons are pressed

glutMotionFunc(), glutPassiveMotionFunc()

Usage:

void glutMotionFunc(void (*func) (int x, int y)); 
void glutPassiveMotionFunc(void (*func) (int x, int y)); 

func //The new motion or passive motion callback function

glutMotionFunc(), glutPassiveMotionFunc()

Sets the mouse enter/leave callback for the current window

glutEntryFunc()

Usage:

void glutEntryFunc(void (*func) (int state));

func //The new entry callback funtion

glutEntryFunc()

The state callback parameter is either GLUT LEFT or GLUT ENTERED depending on if the mouse pointer has last left or entered the window

glutEntryFunc()

Sets the global idle callback

glutIdleFunc()

Sets the global idle callback to be func so a GLUT program can perform background processing tasks or continuous animation when window system events are not being received

glutIdleFunc()

Usage:

void glutIdleFunc(void (*func) (void));

glutIdleFunc()

Registers a timer callback to be triggered in a specified number of milliseconds

glutTimerFunc()

void glutTimerFunc(unsigned int msecs, void (*func) (int value), value);

msecs //Number of milliseconds to pass before calling the callback
func // The timer callback funtion
value // Integer value to pass to the timer callback

glutTimerFunc()

#include <iostream>
#include <windows.h>
#include <GL\glut.h>
#include <GL\freeglut_ext.h>

using namespace std;

void defaultDisplay();
void keyboardMonitor(unsigned char key, int x, int y);
void mouseMonitor(int button, int state, int x, int y);
void detectMotion(int x, int y);
void detectPassiveMotion(int x, int y);
void mouseEntryDetector(int state);
void animateText();
void animateString(int value);

float px, py;

int main(int argc, char **argv){
    glutInit(&argc, argv);
    glutInitWindowSize(1024,768);
    glutInitWindowPosition(200,50);

    glutCreateWindow("My First OpenGL");
    //glutFullScreen();
    glutDisplayFunc(defaultDisplay);
    glutKeyboardFunc(keyboardMonitor);
    glutMouseFunc(mouseMonitor);
    glutMotionFunc(detectMotion);
    glutPassiveMotionFunc(detectPassiveMotion);
    glutEntryFunc(mouseEntryDetector);
    //glutIdleFunc(animateText);
    glutMainLoop();

    return 0;
}

void mouseEntryDetector(int state) {
    if (state == GLUT_LEFT){
        cout << "Mouse has left the application " <<endl;
    } else{
        cout << "Mouse has re-entered the application " << endl;
    }
}
void animateString(int value) {
    if (value==1) {
        px += 0.02;
    } else{
        px -= 0.02;
    }
    glutPostRedisplay();
}

void animateText(){
    Sleep(1000);
    px += .02f;
    glutPostRedisplay();
}
    void detectMotion(int x, int y){
        cout << x << " " << y << endl;
}
    void detectPassiveMotion(int x, int y){
        cout << x << "P " << y << endl;
}

void mouseMonitor(int button, int state, int x, int y) {
    if (button == GLUT_LEFT_BUTTON) {
        if ( state == GLUT_DOWN)
            cout << "Left button was clicked..." << endl;
        else
            cout << "Left button was released..." << endl;
    } else if(button == GLUT_RIGHT_BUTTON) {
        cout << "Right button was clicked..." << endl;
    } else{
        cout << "Middle button was clicked..." << endl;
    }
        cout << x << " " << y << endl;
        //cout << button << endl;
}

void keyboardMonitor(unsigned char key, int x, int y){
    cout << key << endl;
    switch(key){
        case 'a':
            px -= .02f;
            break;
        case 'd':
            px += .02f;
            break;

        default:
            px=0.0f;
    }
    glutPostRedisplay();
}

void defaultDisplay(){
    glClear(GL_COLOR_BUFFER_BIT);

    const unsigned char str[100] = "FEU-TECH";
    glColor3f(0.0f,0.0f,1.0f);
    glRasterPos2f(px,py);
    glutBitmapString(GLUT_BITMAP_HELVETICA_18, str);

    glFlush();

    glutTimerFunc(1000,animateString,2);
}

Sample Program