Question

purpose, you may use the GL_POINTS primitive.Write a program in C/C++ to draw the following points: (0.0,0.0), (20.0,0.0), (20.0,20.0), (0.0,20.0) and (10.0,25.0). For this purpose, you may use the GL_POINTS primitive.​

Answer 1

Introductory program; just a static picture of a colored triangle.
Shows how to use GLUT.
Has minimal structure: only main() and a display callback.
Uses only the default viewing parameters (in fact, it never mentions viewing at all). This is an orthographic view volume with bounds of -1..1 in all three dimensions.
Draws only using glColor and glVertex within glBegin and glEnd in the display callback.
Uses only the GL_POLYGON drawing mode.
Illustrates glClear and glFlush.
triangle.cpp
// A simple introductory program; its main window contains a static picture
// of a triangle, whose three vertices are red, green and blue. The program
// illustrates viewing with default viewing parameters only.

#ifdef __APPLE_CC__
#include
#else
#include
#endif

// Clears the current window and draws a triangle.
void display() {

// Set every pixel in the frame buffer to the current clear color.
glClear(GL_COLOR_BUFFER_BIT);

// Drawing is done by specifying a sequence of vertices. The way these
// vertices are connected (or not connected) depends on the argument to
// glBegin. GL_POLYGON constructs a filled polygon.
glBegin(GL_POLYGON);
glColor3f(1, 0, 0); glVertex3f(-0.6, -0.75, 0.5);
glColor3f(0, 1, 0); glVertex3f(0.6, -0.75, 0);
glColor3f(0, 0, 1); glVertex3f(0, 0.75, 0);
glEnd();

// Flush drawing command buffer to make drawing happen as soon as possible.
glFlush();
}

// Initializes GLUT, the display mode, and main window; registers callbacks;
// enters the main event loop.
int main(int argc, char** argv) {

// Use a single buffered window in RGB mode (as opposed to a double-buffered
// window or color-index mode).
glutInit(&argc, argv);
glutInitDisplayMode(GLUT_SINGLE | GLUT_RGB);

// Position window at (80,80)-(480,380) and give it a title.
glutInitWindowPosition(80, 80);
glutInitWindowSize(400, 300);
glutCreateWindow("A Simple Triangle");

// Tell GLUT that whenever the main window needs to be repainted that it
// should call the function display().
glutDisplayFunc(display);

// Tell GLUT to start reading and processing events. This function
// never returns; the program only exits when the user closes the main
// window or kills the process.
glutMainLoop();
}