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Bobby253
02-06-2010, 05:17 PM
Hey everybody,

I am suppose to write a program for class. But I have difficulties with the glutKeyboardFunc.
I want that the background color changes when I press 'w' or 'r'.
I wrote following codepart for this



void tasten (unsigned char key, int xmouse, int ymouse)
{
switch (key){
case 'w':
glClearColor (1.0, 0.0, 0.0, 0.0);
break;

case 'r':
glClearColor (0.0, 1.0, 0.0, 0.0);
break;

default:
break;
}
}


The problem if that if I open it and press a key than nothing will happen. It only changes its color when I press the 'w' or 'r' key and then the mouse.
Do I use the wrong function or do I do anything else worng?
Thank you for helping.
Bobby253

Here is the whole code in case you need it:


#include <stdlib.h>
#include <GL/glut.h> /* includes the necissarie libaries, etc*/

static GLfloat spin = 0.0;

void init(void)
{
glClearColor (0.0, 0.0, 0.0, 0.0);
glShadeModel (GL_FLAT);
}

void display(void)
{
glClear(GL_COLOR_BUFFER_BIT);
glPushMatrix();
glRotatef(spin, 0.0, 0.0, 1.0);
glColor3f(1.0, 1.0, 1.0);
glBegin(GL_POLYGON);
glVertex2f(-25.0, -25.0);
glVertex2f(-25.0, 25.0);
glVertex2f(25.0, 25.0);
glVertex2f(25.0, -25.0);
glVertex2f(0.0, 40.0);
glEnd();
glPopMatrix();
glutSwapBuffers();
}

void spinDisplay(void)
{
spin = spin + 0.10;
if (spin > 360.0)
spin = spin - 360.0;
glutPostRedisplay();
}

void spinDisplay2(void)
{
spin = spin - 0.10;
if (spin > 360.0)
spin = spin - 360.0;
glutPostRedisplay();
}

void reshape(int w, int h)
{
glViewport (0, 0, (GLsizei) w, (GLsizei) h);
glMatrixMode(GL_PROJECTION);
glLoadIdentity();
glOrtho(-50.0, 50.0, -50.0, 50.0, -1.0, 1.0);
glMatrixMode(GL_MODELVIEW);
glLoadIdentity();
}

void tasten (unsigned char key, int xmouse, int ymouse)
{
switch (key){
case 'w':
glClearColor (1.0, 0.0, 0.0, 0.0);
break;

case 'r':
glClearColor (0.0, 1.0, 0.0, 0.0);
break;

default:
break;
}
}

void motionleft (int mousex,int mousey)
{

static int lx, ly;
if (!lx) lx=mousex; //worng : only choosen first time
if (!ly) ly=mousey;
int dy;
dy=ly-mousey; //wrong: only measures movments
spin=spin+dy*0.1;

}

void mouse(int button, int state, int x, int y)
{
switch (button) {
case GLUT_LEFT_BUTTON:
if(state == GLUT_DOWN);
glutIdleFunc(spinDisplay);
if (state == GLUT_DOWN)
glutMotionFunc(motionleft);
if (state == GLUT_UP)
glutIdleFunc(NULL);
if (state == GLUT_UP)
glutMotionFunc(NULL);
break;
case GLUT_RIGHT_BUTTON:
if (state == GLUT_DOWN)
glutIdleFunc(spinDisplay2);
if (state == GLUT_UP)
glutIdleFunc(NULL);
break;
default:
break;
}
}



int main(int argc, char** argv)
{
glutInit(&amp;argc, argv);
glutInitDisplayMode (GLUT_DOUBLE | GLUT_RGB);
glutInitWindowSize (250, 250);
glutInitWindowPosition (100, 100);
glutCreateWindow ("Julia Gaa - Assignment 2");
init ();
glutDisplayFunc(display);
glutReshapeFunc(reshape);
glutKeyboardFunc(tasten);
glutMouseFunc(mouse);
glutMainLoop();
return 0;
}

marshats
02-06-2010, 08:09 PM
The way you are setting and un-setting your Idle function you are not continuously redrawing the screen. You are only redrawing the screen when the mouse button is down. Thats OK but as a consequence you need to request the window to be redrawn explicitly when you change colors on a key press ie add a glutPostRedisplay



void tasten (unsigned char key, int xmouse, int ymouse)
{
switch (key){
case 'w':
glClearColor (1.0, 0.0, 0.0, 0.0);
break;

case 'r':
glClearColor (0.0, 1.0, 0.0, 0.0);
break;

default:
break;
}
glutPostRedisplay(); //request display() call ASAP
}

Bobby253
02-06-2010, 08:24 PM
Hey Marshats,

Thank you.
Now it works like I wanted to have it.
Thank you.

Bobby253