3d Tank

package lwjgl02;

import org.lwjgl.Sys;
import org.lwjgl.LWJGLException;
import org.lwjgl.opengl.Display;
import org.lwjgl.opengl.DisplayMode;
import org.lwjgl.input.Keyboard;
import static org.lwjgl.opengl.GL11.*;

public class LWJGL02 {

    public static void main(String[] args) {
        LWJGL02 lw = new LWJGL02();
        lw.start();
    }
    final int SCREEN_WIDTH = 640; // Screen width
    final int SCREEN_HEIGHT = 480; // Screen height
    final int SCREEN_DEPTH = 50;  // Screen Depth
    final int SCALE = 3; // Screen Scale

    long lastFrame;
    long lastFPS;
    int fps;

    public void start() {
        try {
            Display.setDisplayMode(new DisplayMode(SCREEN_WIDTH, SCREEN_HEIGHT));
            Display.setVSyncEnabled(true);
            Display.create();
        } catch (LWJGLException e) {
            e.printStackTrace();
            System.exit(0);
        }
        lastFPS = getTime(); // Init FPS

        getDelta(); // init last frame
        glMatrixMode(GL_PROJECTION);
        glLoadIdentity();
        glOrtho(-4 * SCALE, 4 * SCALE, -3 * SCALE, 3 * SCALE, SCREEN_DEPTH, -SCREEN_DEPTH);
        glMatrixMode(GL_MODELVIEW);
        float x_flag = 0;
        float y_flag = 0;
        float z_flag = 0;
        float angle = 0;

        // Loop begin ~
        while (!Display.isCloseRequested()) {
            if (Keyboard.isKeyDown(Keyboard.KEY_DOWN)) {
                x_flag += 1;
            }
            if (Keyboard.isKeyDown(Keyboard.KEY_UP)) {
                x_flag -= 1;
            }
            if (Keyboard.isKeyDown(Keyboard.KEY_LEFT)) {
                y_flag += 1;
            }
            if (Keyboard.isKeyDown(Keyboard.KEY_RIGHT)) {
                y_flag -= 1;
            }
            if (Keyboard.isKeyDown(Keyboard.KEY_Q)){
                z_flag += 1;
            }
            if (Keyboard.isKeyDown(Keyboard.KEY_W)){
                z_flag -= 1;
            }
            if (Keyboard.isKeyDown(Keyboard.KEY_1)){
                angle += 1;
            }
            if (Keyboard.isKeyDown(Keyboard.KEY_2)){
                angle -= 1;
            }
            if (Keyboard.isKeyDown(Keyboard.KEY_X)){
                x_flag = 0;
                y_flag = 0;
                z_flag = 0;
                angle =  0;
            }
            clear_screen();
            glPolygonMode(GL_FRONT_AND_BACK, GL_LINE);
            glPushMatrix();
            System.out.printf("%2f:%2f:%2f:%2f\n",angle,x_flag,y_flag,z_flag);
            glRotated(angle,x_flag,y_flag,z_flag);
//            glRotated(angle,1,1,0);
            trapesium(6,5  ,0  ,2  ,0,1, true,true);
            trapesium(6,5  ,0  ,2  ,5,1, true,true);
            trapesium(5,4.5,0.3,1.4,1,4, true,false);
            glTranslated(1,0,0);
            trapesium(2.5 ,2.0 ,1.4 ,3 ,1.7 ,2.7, false,false);
            trapesium(1.0 ,0.5 ,3 ,3.5 ,2 ,1 , false,false);
            trapesium2(-2.4, -2.1, 1.4 + 0.4, 3 - 0.4, -5, 2.3,1.3);

            glPopMatrix();
            Display.update();
            Display.sync(60);
            updateFPS();
        }
        Display.destroy();
    }

    void clear_screen() {
        glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
    }

    long getTime() {
        return (Sys.getTime() * 1000) / Sys.getTimerResolution();
    }

    long getDelta(){
        long time = getTime();
        int delta = (int)(time - lastFrame);
        lastFrame = time;
        return delta;
    }

    void updateFPS(){
        if(getTime() - lastFPS > 1000){
            Display.setTitle("FPS: " + fps);
            fps = 0;
            lastFPS += 1000;
        }
        fps++;
    }

    void trapesium(double x1, double x2, double y1, double y2,
            double depth, double depth_plus, boolean mirror, boolean reduce){

        double depth2 =  depth + depth_plus;
        glBegin(GL_QUADS);

        glVertex3d(-x1,y1,depth);
        glVertex3d(x1,y1,depth);
        glVertex3d(x2,y2,depth);
        glVertex3d(-x2,y2,depth);

        glVertex3d(-x1,y1,depth);
        glVertex3d(-x2,y2,depth);
        glVertex3d(-x2,y2,depth2);
        glVertex3d(-x1,y1,depth2);

        glVertex3d(x1,y1,depth);
        glVertex3d(x2,y2,depth);
        glVertex3d(x2,y2,depth2);
        glVertex3d(x1,y1,depth2);

        glVertex3d(-x1,y1,depth2);
        glVertex3d(x1,y1,depth2);
        glVertex3d(x2,y2,depth2);
        glVertex3d(-x2,y2,depth2);

        if (mirror){

        if (reduce){
        x1 -= 1;
        x2 -= 0.75;
        }
        y2 -= 0.5;

        y2 = -y2;

        glVertex3d(-x1,y1,depth);
        glVertex3d(x1,y1,depth);
        glVertex3d(x2,y2,depth);
        glVertex3d(-x2,y2,depth);

        glVertex3d(-x1,y1,depth);
        glVertex3d(-x2,y2,depth);
        glVertex3d(-x2,y2,depth2);
        glVertex3d(-x1,y1,depth2);

        glVertex3d(x1,y1,depth);
        glVertex3d(x2,y2,depth);
        glVertex3d(x2,y2,depth2);
        glVertex3d(x1,y1,depth2);

        glVertex3d(-x1,y1,depth2);
        glVertex3d(x1,y1,depth2);
        glVertex3d(x2,y2,depth2);
        glVertex3d(-x2,y2,depth2);
        }
        glEnd();
    }

    void trapesium2(double x1, double x2, double y1, double y2, double length,
            double depth, double depth_plus){
        double depth2 =  depth + depth_plus;
        glBegin(GL_QUADS);

        glVertex3d(x1,y1,depth);
        glVertex3d(x2,y2,depth);
        glVertex3d(x1 + length,y2,depth);
        glVertex3d(x1 + length,y1,depth);

        glVertex3d(x1,y1,depth);
        glVertex3d(x2,y2,depth);
        glVertex3d(x2,y2,depth2);
        glVertex3d(x1,y1,depth2);

        glVertex3d(x1 + length,y1,depth);
        glVertex3d(x1 + length,y2,depth);
        glVertex3d(x1 + length,y2,depth2);
        glVertex3d(x1 + length,y1,depth2);

        glVertex3d(x1,y1,depth2);
        glVertex3d(x2,y2,depth2);
        glVertex3d(x1 + length,y2,depth2);
        glVertex3d(x1 + length,y1,depth2);

        glEnd();
    }

}