Making a simple shape move in opengl

[adriyel]

Hello guys. I wanna make the body (square) move left when I press the left arrow key. Unfortunately, it's in data structures and I don't know what to put in the "void SpecialKeys(int key, int x, int y)" part to make it move. Any help would be good. :) By the way, I'm just a beginner. Our prof explain this but it's still kind of a blur and I wanna learn as much as possible. Cheers!


#include <vector>
#include <time.h>

using namespace std;

#include "Glut_Setup.h"



struct Vertex
{
float x,y,z;
};

Vertex Body []=
{
(-0.5, -2, 0),
(0.5, -2, 0),
(0.5, -3, 0),
(-0.5, -3, 0)
};




void GameScene()
{
glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);





glBegin(GL_QUADS);
glColor3f(0.0, 0.0, 1.0);
glVertex3f(-0.5, -2, 0);
glVertex3f(0.5, -2, 0);
glVertex3f(0.5, -3, 0);
glVertex3f(-0.5, -3, 0);
glEnd();







glutSwapBuffers();
}

void Keys(unsigned char key, int x, int y)
{
switch(key)
{

}
}

void SpecialKeys(int key, int x, int y)
{
switch(key)
{

}
}

[NGangst]

Hi Adriyel,

here you are using the GLUT library as opposed to just OpenGL.

One of the ways GLUT helps you here is that it provides defines for your input keys allready:
GLUT_KEY_LEFT
GLUT_KEY_UP
GLUT_KEY_RIGHT
GLUT_KEY_DOWN

these are defined in the glut.h header

for something bigger you would want to write a more advanced input handler but for this its good enough to just add a some cases to your switch.

switch(key)
{
 case GLUT_KEY_LEFT:
break;
}

[NGangst]

for moving the square, there are two ways to do it, a right way and a wrong way.

In theory you can store a variable for your x_offset and just add to it every time the user has pressed the left key.

then in this block:

glBegin(GL_QUADS);
glColor3f(0.0, 0.0, 1.0);
glVertex3f(-0.5, -2, 0);
glVertex3f(0.5, -2, 0);
glVertex3f(0.5, -3, 0);
glVertex3f(-0.5, -3, 0);
glEnd();

you could just add your xoffset to each x value

glBegin(GL_QUADS);
glColor3f(0.0, 0.0, 1.0);
glVertex3f(x_offset+ -0.5, -2, 0);
glVertex3f(x_offset+ 0.5, -2, 0);
glVertex3f(x_offset+ 0.5, -3, 0);
glVertex3f(x_offset+ -0.5, -3, 0);
glEnd();

BUT the more "correct" method is to use the OpenGL transforms.

glPushMatrix(); 

glLoadIdentity ()
glTranslatef(x_offset, 0.0f, 0.0f) 

glBegin(GL_QUADS);
glColor3f(0.0, 0.0, 1.0);
glVertex3f(x_offset+ -0.5, -2, 0);
glVertex3f(x_offset+ 0.5, -2, 0);
glVertex3f(x_offset+ 0.5, -3, 0);
glVertex3f(x_offset+ -0.5, -3, 0);
glEnd();

glPopMatrix();

I hope this helps, thanks -NGangst