OpenGL - Calling square function with different colour - c++

Question

I have made a drawSquare() function that draws several 2D squares on my screen:
void drawSquare(GLfloat length, GLfloat x, GLfloat y, GLfloat outline){
// x1,y1 is the top left-hand corner coordinate
// and so on...
GLfloat x1, y1, x2, y2, x3, y3, x4, y4;
x1 = x - length / 2;
y1 = y + length / 2;
x2 = x + length / 2;
y2 = y + length / 2;
x3 = x + length / 2;
y3 = y - length / 2;
x4 = x - length / 2;
y4 = y - length / 2;
// ACTUAL SQUARE OBJECT
glColor3f(0.0, 1.0, 1.0); // Colour: Cyan
glBegin(GL_POLYGON);
glVertex2f(x1, y1); // vertex for BLUE SQUARES
glVertex2f(x2, y2);
glVertex2f(x3, y3);
glVertex2f(x4, y4);
glEnd()
}
When I click a square, I need its colour to change. I already have a mouse function set up that displays the mouse location when I right click:
void processMouse(int button, int state, int x, int y)
{
if ((button == GLUT_LEFT_BUTTON) && (state == GLUT_DOWN)){
// gets mouse location
printf("Clicked on pixel %d - %d", x, y);
// prints to console
}
}
and an if statement inside the above if statement like this:
if (x > 0 && x < 95 && y > 302 && y < 395) {
// there's a square at this location!
// change the square colour!
}
When I place exit(0); inside this statement:
if (x > 0 && x < 95 && y > 302 && y < 395) {
exit(0);
}
My program exits fine, so the condition works, I just want to know how I can somehow call my drawSquare() function again with a different colour.
Initially when I call my drawSquare(), it's called in my display function like this:
void display(){
glClear(GL_COLOR_BUFFER_BIT); /* clear window */
// there are some other primatives here too
drawSquare(100,150, 750,true); // square drawn
}
SOLUTION
Here's how I fixed my issue. I made a global boolean variable boolean variable areaClicked = false; that checks if user has clicked, we set as false by default.
In my mouse function, I check if a square has been clicked, if so, set the boolean to true:
if (x >= 0 && x <= 95 && y >= 302 && y <= 380) { // area of box
areaClicked = true;
}
Now in my display function, we check if the boolean has been triggered, if it has, then display my recoloured square, otherwise, do nothing:
if (areaClicked != false) {
drawRecolour(100, 50, 350, true); // 4th square drawn
}
else areaClicked = false;

Answer 1

In your event handler set a variable, then trigger a redraw.
if (x > 0 && x < 95 && y > 302 && y < 395) {
// there's a square at this location!
// change the square colour!
square_color = ...;
glutPostRedisplay();
}
In your display function check for the variable and use that to determine the color:
// you should probably make the color a parameter of drawSquare
void drawSquare(GLfloat length, GLfloat x, GLfloat y, GLfloat outline){
// OpenGL doesn't do "objects". It **DRAWS** things. Like pen on paper
glColor3f(square_color); // <---- uses variable
glBegin(GL_POLYGON);
...
glEnd()
}