OpenGL - How to draw multiple different 2D shapes using pop-up menu? - opengl

Question

I'm trying to make a simple openGL application which creates shapes using mouse clicks. The shape required is selected using a pop-up menu opened using the right mouse button. Currently I have rectangle working and also a simple paint-esque function using points. They disappear once redrawn but that's a problem I'll worry about in the future.
Currently I'm trying to also implement a Line function as a menu option. I have the below code in place but when I select the Line option from the pop-up menu and click two points it doesn't seem to draw a line as expected. Can anyone point out where I'm going wrong here?
GLfloat x1, x2, y1, y2;
GLfloat x_Src, y_Src, x_Dest, y_Dest;
//used to change colour (To be implemented)
static int colour;
void menu(int);
void display(void)
{
glClearColor(0.0, 2.0, 1.0, 1.0);
glClear(GL_COLOR_BUFFER_BIT);
glPointSize(3.0);
glColor3f(1.0, 0.0, 0.0);
//Rectangle vertices
glBegin(GL_POLYGON);
glVertex2f(x1, y1);
glVertex2f(x1, y2);
glVertex2f(x2, y2);
glVertex2f(x2, y1);
glEnd();
//Line vertices
glColor3f(0.0, 0.0, 1.0);
glBegin(GL_LINE);
glVertex2f(x_Src, y_Src);
glVertex2f(x_Dest, y_Dest);
glEnd();
glFlush();
return;
}
void MyRect(GLint button, GLint state, GLint x, GLint y)
{
static int first = 1;
if (state == GLUT_DOWN && button == GLUT_LEFT_BUTTON)
{
if (first)
{
//first point in terms of window size
x1 = (x - 250.0) / 250.0;
y1 = -(y - 250) / 250.0;;
}
else
{
//second point in terms of window size
x2 = (x - 250.0) / 250.0;
y2 = -(y - 250) / 250.0;
glutPostRedisplay();
}
first = !first;
}
return;
}
void MyLine(GLint button, GLint state, GLint x, GLint y)
{
static int first = 1;
if (state == GLUT_DOWN && button == GLUT_LEFT_BUTTON)
{
if (first)
{
x_Src = (x - 250.0) / 250.0;
y_Src = -(y - 250) / 250.0;
}
else
{
x_Dest = (x - 250.0) / 250.0;
y_Dest = -(y - 250) / 250.0;
glutPostRedisplay();
}
first = !first;
}
return;
}
//allows drawing of un-fixed line using mouse
void MyPaint(GLint x, GLint y)
{
glColor3f(0.0, 0.0, 0.0);
glPointSize(3.0);
glBegin(GL_POINTS);
glVertex2f((x - 250.0) / 250.0, -(y - 250.0) / 250.0);
glEnd();
glFlush();
return;
}
void MainMenu(int item)
{
//Remove motion function if exists and go to rectangle function
//prevents two functions running at once
if (item == 1)
{
glutMotionFunc(NULL);
glutMouseFunc(MyRect);
}
else if (item == 2)
{
glutMotionFunc(NULL);
glutMouseFunc(MyLine);
}
else if (item == 5)
{
glutMouseFunc(NULL);
glutMotionFunc(MyPaint);
}
glutPostRedisplay();
return;
}
int main(int argc, char **argv)
{
glutInit(&argc, argv);
glutInitWindowSize(500, 500);
glutInitWindowPosition(500, 200);
glutCreateWindow("Draw Shapes");
glutDisplayFunc(display);
glutCreateMenu(MainMenu);
glutAddMenuEntry("Rectangle", 1);
glutAddMenuEntry("Line", 2);
glutAddMenuEntry("Circle", 3);
glutAddMenuEntry("Triangle", 4);
glutAddMenuEntry("Paintbrush", 5);
glutAddMenuEntry("Background colour", 6);
glutAddMenuEntry("Clear screen", 7);
glutAttachMenu(GLUT_RIGHT_BUTTON);
glutMainLoop();
}

Answer 1

You need to use glBegin(GL_LINES) instead of glBegin(GL_LINE).
GL_LINE is an argument to the unrelated function glPolygonMode.