Use arrow keys to rotate refrence system in openGL - visual-studio-2010

Question

This is the code written in the book openGL SuperBible to create a Spring-Shaped Path of Points on the screen:
#include "stdafx.h"
#include <Windows.h>
#include <gl\glut.h>
#include <gl\GLU.h>
#include <gl\GL.h>
#include <math.h>
// Define a constant for the value of PI
#define GL_PI 3.1415f
void ChangeSize(GLsizei , GLsizei );
void SetupRC();
void RenderScene(void);
int main(int argc, CHAR* argv[])
{
glutInit(&argc, argv);
glutInitDisplayMode(GLUT_DOUBLE | GLUT_RGB);
glutCreateWindow("Points Example");
glutDisplayFunc(RenderScene);
glutReshapeFunc(ChangeSize);
SetupRC();
glutMainLoop();
return 0;
}
// Change viewing volume and viewport. Called when window is resized
void ChangeSize(GLsizei w, GLsizei h)
{
GLfloat nRange = 100.0f;
// Prevent a divide by zero
if(h == 0)
h = 1;
// Set Viewport to window dimensions
glViewport(0, 0, w, h);
// Reset projection matrix stack
glMatrixMode(GL_PROJECTION);
glLoadIdentity();
// Establish clipping volume (left, right, bottom, top, near, far)
if (w <= h)
glOrtho (-nRange, nRange, -nRange*h/w, nRange*h/w, -nRange, nRange);
else
glOrtho (-nRange*w/h, nRange*w/h, -nRange, nRange, -nRange, nRange);
// Reset Model view matrix stack
glMatrixMode(GL_MODELVIEW);
glLoadIdentity();
}
// This function does any needed initialization on the rendering context
void SetupRC()
{
// Black background
glClearColor(0.0f, 0.0f, 0.0f, 1.0f );
// Set drawing color to green
glColor3f(0.0f, 1.0f, 0.0f);
}
// Called to draw scene
void RenderScene(void)
{
GLfloat x,y,z,angle;
int xRot,yRot; // Storage for coordinates and angles
xRot = 45;
yRot = 45;
// Clear the window with current clearing color
glClear(GL_COLOR_BUFFER_BIT);
// Save matrix state and do the rotation
glPushMatrix();
glRotatef(xRot, 1.0f, 0.0f, 0.0f);
glRotatef(yRot, 0.0f, 1.0f, 0.0f);
// Call only once for all remaining points
glBegin(GL_POINTS);
z = -50.0f;
for(angle = 0.0f; angle <= (2.0f*GL_PI)*3.0f; angle += 0.1f)
{
x = 50.0f*sin(angle);
y = 50.0f*cos(angle);
// Specify the point and move the Z value up a little
glVertex3f(x, y, z);
z += 0.5f;
}
// Done drawing points
glEnd();
// Restore transformations
glPopMatrix();
// Flush drawing commands
glutSwapBuffers();
}
In fact by setting xRot=yRot=45 degrees, I have reached this shape.
But in the book it is told:
When this program is run, all you see is a circle
of points because you are initially looking directly down the z-axis. To see the effect, use
the arrow keys to spin the drawing around the x- and y-axes.
This means that we should have some code using arrow keys to increase and decrease the value of xRot and yRot. I have made some effort to do that.
1-Writing a function:
void _cdecl keyboard(int key ,int xRot,int yRot)
{
switch (key)
{
case GLUT_KEY_PAGE_UP:
yRot++;
case GLUT_KEY_PAGE_DOWN:
yRot--;
case GLUT_KEY_HOME:
xRot--;
case GLUT_KEY_END:
xRot++;
}
}
2-Its prototype at top of the code:
void _cdecl keyboard(int,int,int);
3-adding these two lines of code to the body of the function RenderScene:
GLint key = GLUT_KEY_PAGE_UP;
glutSpecialFunc(keyboard(key,xRot,yRot));
But I'm not sure it will work. The code gets the error:
error C2664: 'glutSpecialFunc' : cannot convert parameter 1 from 'void' to 'void (__cdecl *)(int,int,int)'
and I don't know how to return the changed value of xRot and yRot to the caller function because the compiler doesn't let me to define Pass by referrence parameters and the argument of glutSpecialFunc is a pointer to a void function!
Edited section of my question
as jblocksom suggested I changed the code to something like this:
1-defining and initializing global variables just before the main starts:
int xRot = 0;
int yRot = 0;
2- calling glutSpecialFunc somewhere in main
glutSpecialFunc(keyboard);
glutDisplayFunc(RenderScene);
glutReshapeFunc(ChangeSize);
3- altering the code in keyboard function
void keyboard(int keyParam ,int mx,int my)
{
switch (keyParam)
{
case GLUT_KEY_PAGE_UP:
my++;
case GLUT_KEY_PAGE_DOWN:
my--;
case GLUT_KEY_HOME:
mx--;
case GLUT_KEY_END:
mx++;
}
glutPostRedisplay();
}
No compile and run-time error. But it does not work. I think this is because when I call glutSpecialFunc(keyboard), the function uses coordinates of mouse and keypress as the input argument so any increment or decrement is applied on the mouse coordinates not xRot or yRot which will be used in glRotatef(xRot, 1.0f, 0.0f, 0.0f) or glRotatef(yRot, 0.0f, 1.0f, 0.0f) so when calling the two latter the xRot and yRot is still equal to zero and there will be no rotation.I need to pass xRot and yRot to the function keyboard but how???
Even writing the function as:
void keyboard(int keyParam ,int mx,int my)
{
switch (keyParam)
{
case GLUT_KEY_PAGE_UP:
yRot++;
case GLUT_KEY_PAGE_DOWN:
yRot--;
case GLUT_KEY_HOME:
xRot--;
case GLUT_KEY_END:
xRot++;
}
glutPostRedisplay();
}
and calling it in the form glutSpecialFunc(keyboard) will not any difference!!!

Answer 1

glutSpecialFunc registers a callback with GLUT to be called when the user hits one of the arrow keys; the function you give it, keyboard, is not something you would call yourself. This is why you can't return anything from it. To get data out of the callback you'll need to set a global variable.
You'll want to call glutSpecialFunc somewhere in main where the other GLUT callbacks are set (eg glutRenderFunc). To get past the compile error, you'll call it like this:
glutSpecialFunc(keyboard);
which tells GLUT to call keyboard() with the key and mouse position.
Make the xRot and yRot variables referred to in RenderScene global.
Change the function signature of keyboard to not use xRot and yRot as variable names so that it will refer to the global ones:
void _cdecl keyboard(int key, int mx, int my)
You'll also probably need a call to glutPostRedisplay() at the end of keyboard, this will tell GLUT to redraw the scene.
Hopefully after that it should work, good luck!