Explain the operations for displaying a picture using GLUT

2.B] Explain the operations for displaying a picture using GLUT.

Answer:

Here’s a complete example in C++ that demonstrates how to display a square using GLUT:

#include <GL/glut.h>

// Function to display the square
void display() {
    // Clear the screen
    glClear(GL_COLOR_BUFFER_BIT);

    // Set the color of the square (red)
    glColor3f(1.0, 0.0, 0.0);

    // Begin drawing a polygon (square)
    glBegin(GL_POLYGON);

    // Specify the vertices of the square
    glVertex2f(-0.5f, -0.5f);  // Bottom left
    glVertex2f(0.5f, -0.5f);   // Bottom right
    glVertex2f(0.5f, 0.5f);    // Top right
    glVertex2f(-0.5f, 0.5f);   // Top left

    // End drawing
    glEnd();

    // Flush the graphics pipeline
    glFlush();
}

// Main function
int main(int argc, char** argv) {
    // Initialize GLUT
    glutInit(&argc, argv);

    // Set the display mode (single buffer and RGB color)
    glutInitDisplayMode(GLUT_SINGLE | GLUT_RGB);

    // Set the window size
    glutInitWindowSize(500, 500);

    // Set the window position
    glutInitWindowPosition(100, 100);

    // Create the window with a title
    glutCreateWindow("Display a Square");

    // Set the background color to white
    glClearColor(1.0, 1.0, 1.0, 1.0);

    // Set up the projection (orthographic 2D)
    glMatrixMode(GL_PROJECTION);
    glLoadIdentity();
    gluOrtho2D(-1.0, 1.0, -1.0, 1.0);

    // Register the display callback function
    glutDisplayFunc(display);

    // Enter the GLUT event-processing loop
    glutMainLoop();

    return 0;
}

Explanation:

Include GLUT Header:

• #include <GL/glut.h>: This includes the GLUT library needed to create windows, handle user input, and display graphics.

Display Function:

• The display() function contains the code to render a square.
• glClear(GL_COLOR_BUFFER_BIT): Clears the screen before drawing.
• glColor3f(1.0, 0.0, 0.0): Sets the color of the square to red.
• glBegin(GL_POLYGON) and glEnd(): These functions define the vertices of the square.
• glFlush(): Ensures that all OpenGL commands are executed.

Main Function:

• Initialization: glutInit(&argc, argv); initializes GLUT.
• Display Mode: glutInitDisplayMode(GLUT_SINGLE | GLUT_RGB); sets the display mode to single buffering with RGB color.
• Window Setup: glutInitWindowSize() and glutInitWindowPosition() define the size and position of the window.
• Create Window: glutCreateWindow("Display a Square"); creates a window with the specified title.
• Background Color: glClearColor(1.0, 1.0, 1.0, 1.0); sets the background color to white.
• Projection: glMatrixMode(GL_PROJECTION);, glLoadIdentity();, and gluOrtho2D() set up a simple orthographic projection that allows you to specify coordinates in 2D.
• Display Callback: glutDisplayFunc(display); registers the display() function as the callback for rendering.
• Main Loop: glutMainLoop(); starts the GLUT event loop, which waits for events like window resizing or redrawing and calls the appropriate callback functions.