I have been searching all day for a tutorial or example code for a simple program - click on object (like a 2D rectangle for example) then as you hold and move the mouse the object follows the mouse, then on mouse release the object remains in new location. In other words, I want to understand how to drag and drop an object with the mouse events.
Could anyone help to point me in the right direction of any useful sources of information relating to this problem?
Thanks for all the responses so far.
I have worked out how to do it, so I will go ahead an answer my own question.
I am using GLUT as a mouse handler:
When the mouse is clicked and moving (glutMotionFunc) the drag function is called.
In the drag function the mouse coordinates (x,y) are converted to a Points struct while being converted into window coordinates.
If the mouse is within the square then drag the square by changing it's coordinates and redisplay.
I am still very new to OpenGL and C++ so I do apologize for the messy coding. I am a bit frustrated in doing it this way as the redrawn square makes it seem the cursor snaps to the center. I welcome alternative solutions to this problem and criticism of my code, for learning purposes.
CODE (included glut and using namespace std):
// points structure made of two coordinates; x and y
struct Points
{
float x,y; // initializor
Points() { x = 0.0; y = 0.0; } // constructor
Points(float _x, float _y) : x(_x), y(_y) {}
};
// square made of 4 points
class Square
{
public:
Points pts[4]; // square structure
Square(); // initialize constructor
void draw(Square *sqr); // draw square
Points mouse(int x, int y); // get mouse coordintaes
Square* drag(Square *sqr, Points *mouse); // change points of sqr
};
// square constructor
Square::Square()
{
pts[0] = Points(0.2,0.2);
pts[1] = Points(0.4,0.2);
pts[2] = Points(0.4,0.4);
pts[3] = Points(0.2,0.4);
};
// draw function
void Square::draw(Square *sqr)
{
// draw square fill
int i;
glColor3f(0.2, 0.2, 0.2);
glBegin(GL_QUADS);
for (i = 0; i < 4; ++i)
{
glVertex2f(sqr->pts[i].x, sqr->pts[i].y);
}
glEnd();
// draw square points
i = 0;
glColor3f(1.0, 1.0, 1.0);
glBegin(GL_POINTS);
for (i = 0; i < 4; ++i)
{
glVertex2f(sqr->pts[i].x, sqr->pts[i].y);
}
glEnd();
}
// mouse function
Points Square::mouse(int x, int y)
{
int windowWidth = 400, windowHeight = 400;
return Points(float(x)/windowWidth, 1.0 - float(y)/windowHeight);
}
// drag function
Square* Square::drag(Square *sqr, Points *mouse)
{
sqr->pts[0].x = mouse->x - 0.1;
sqr->pts[0].y = mouse->y - 0.1;
sqr->pts[1].x = mouse->x + 0.1;
sqr->pts[1].y = mouse->y - 0.1;
sqr->pts[3].x = mouse->x - 0.1;
sqr->pts[3].y = mouse->y + 0.1;
sqr->pts[2].x = mouse->x + 0.1;
sqr->pts[2].y = mouse->y + 0.1;
return sqr;
}
// GLOBAL
// create square object
Square* sqr = new Square;
// display at start
void display() {
glClear(GL_COLOR_BUFFER_BIT);
sqr->draw(sqr);
glFlush();
}
// drag function
void drag (int x, int y)
{
// int x and y of mouse converts to screen coordinates
// returns the point as mousePt
Points mousePt = sqr->mouse(x,y);
//create pointer to window point coordinates
Points* mouse = &mousePt;
// if the mouse is within the square
if (mouse->x > sqr->pts[0].x && mouse->y > sqr->pts[0].y)
{
if (mouse->x < sqr->pts[2].x && mouse->y < sqr->pts[2].y)
{
// then drag by chaning square coordinates relative to mouse
sqr->drag(sqr,mouse);
glutPostRedisplay();
}
}
}
void Initialize() {
glClearColor(0.0, 0.0, 0.0, 0.0);
glMatrixMode(GL_PROJECTION);
glLoadIdentity();
glOrtho(0.0, 1.0, 0.0, 1.0, -1.0, 1.0);
}
int main(int iArgc, char** cppArgv) {
glutInit(&iArgc, cppArgv);
glutInitDisplayMode(GLUT_SINGLE | GLUT_RGB);
glutInitWindowSize(400, 400);
glutInitWindowPosition(200, 200);
glutCreateWindow("Move Box");
glutMotionFunc(drag);
Initialize();
glutDisplayFunc(display);
glutMainLoop();
return 0;
}
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