Object not rotating

Question

I have a rectangle and this will be the base of my moving object.

I`m trying to rotate the object only when the A button is pressed, when is released the object should stop rotating.

package Tanc;

import org.lwjgl.input.Keyboard;

import org.lwjgl.input.Mouse;

import org.lwjgl.opengl.Display;
import org.lwjgl.opengl.DisplayMode;

import org.lwjgl.opengl.GL11;

import org.lwjgl.LWJGLException;

public class Tanc{

public Tanc(){
    try{
        Display.setDisplayMode(new DisplayMode(640,480));
        Display.setTitle("Tanc");
        Display.create();
    }catch(LWJGLException e){
        e.printStackTrace();
    }
    GL11.glMatrixMode(GL11.GL_MODELVIEW);
    GL11.glLoadIdentity();
    GL11.glOrtho(1, 1, 1, 1, 1, -1);
    GL11.glEnable(GL11.GL_TEXTURE_2D);
    GL11.glMatrixMode(GL11.GL_PROJECTION);
    float y_angle = 0;
    boolean aFlag = false;
    while(!Display.isCloseRequested()){
        GL11.glClear(GL11.GL_COLOR_BUFFER_BIT);
    //  GL11.glPushMatrix();
        GL11.glLoadIdentity();
        GL11.glRectd(0, 0, 0.2f, 0.3f);
        GL11.glTranslatef(0, 0, 0);

        while(Keyboard.next()){
            if(Keyboard.getEventKey() == Keyboard.KEY_A){
                aFlag = true;
            }
        }
        if(aFlag){
            y_angle = 0.1f;
            GL11.glRotatef(y_angle, 0, 0, 1);
        }
        else{
            y_angle = 0;
            GL11.glRotatef(0, 0, 0, 1);
        }




    //  GL11.glPopMatrix();
        Display.update();
        Display.sync(60);
    }   
    Display.destroy();
    System.exit(0);
}

public static void main(String[] args){
    new Tanc();
}

}

vallentin vallentin · Accepted Answer · 2013-10-30T15:47:33

That is because you never really rotate anything. You y_angle doesn't really change other than from 0.0 to 0.1.

Remember that the angle parameter glRotatef() takes, need to be in degrees and not radians. A full circle in radians goes from 0.0 to ~6.2831 radians. Where a full circle using degress goes from 0.0 to 360.0 degress. So your angle isn't noticeable at all, because your only changing it by such a small amount.

I've changed your code. When you now hold the A button, it will rotate and when you release the button it will stop rotating.

float y_angle = 0;

while (!Display.isCloseRequested()) {
    GL11.glClear(GL11.GL_COLOR_BUFFER_BIT);
    GL11.glLoadIdentity();
    GL11.glRectd(0, 0, 0.2f, 0.3f);
    GL11.glTranslatef(0, 0, 0);

    while (Keyboard.next()){
        if (Keyboard.getEventKey() == Keyboard.KEY_A) {
            y_angle += 10f;
        }
    }

    GL11.glRotatef(y_angle, 0, 0, 1);

    Display.update();
    Display.sync(60);
}

Object not rotating

1 Answers