LWJGL 使对象始终面朝上

Question

我需要让 3D 对象以相同的方式正面朝上，无论它们在相机中的位置如何。好像相机距离很远并且放大了。这就是我的意思（看看柱子和墙壁）：http://youtu.be/Pn9fh93oV-c

这是我目前的情况：

package pack;

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

import java.util.Random;

import static org.lwjgl.opengl.GL11.*;
import static org.lwjgl.util.glu.GLU.gluPerspective;

public class Main {

float viewx, viewy;
float angle;

public static void main(String[] args) {
    Main main = new Main();
    main.start();
}

private void start() {
    try {
        Display.setDisplayMode(new DisplayMode(640, 480));
        Display.setTitle("Three Dee Demo");
        Display.create();
    } catch (LWJGLException e) {
        e.printStackTrace();
        Display.destroy();
        System.exit(1);
    }
    glMatrixMode(GL_PROJECTION);
    glLoadIdentity();
    gluPerspective((float) 30, 640f / 480f, 0.001f, 100);
    glMatrixMode(GL_MODELVIEW);
    glEnable(GL_DEPTH_TEST);
    glTranslatef(0, 0, -20);

    while (!Display.isCloseRequested()) {
        glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);

        update();
        render();

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

    Display.destroy();
    System.exit(0);
}

private void render() {

     GL11.glBegin(GL11.GL_QUADS);    
     GL11.glColor3f(1.0f,1.0f,0.0f);           
     GL11.glVertex3f( 1.0f, 1.0f,-1.0f);        
     GL11.glVertex3f(-1.0f, 1.0f,-1.0f);        
     GL11.glVertex3f(-1.0f, 1.0f, 1.0f);
     GL11.glVertex3f( 1.0f, 1.0f, 1.0f);  
     GL11.glColor3f(1.0f,0.5f,0.0f);            
     GL11.glVertex3f( 1.0f,-1.0f, 1.0f);
     GL11.glVertex3f(-1.0f,-1.0f, 1.0f);
     GL11.glVertex3f(-1.0f,-1.0f,-1.0f);
     GL11.glVertex3f( 1.0f,-1.0f,-1.0f);
     GL11.glColor3f(1.0f,0.0f,0.0f);
     GL11.glVertex3f( 1.0f, 1.0f, 1.0f);
     GL11.glVertex3f(-1.0f, 1.0f, 1.0f);
     GL11.glVertex3f(-1.0f,-1.0f, 1.0f);
     GL11.glVertex3f( 1.0f,-1.0f, 1.0f);
     GL11.glColor3f(1.0f,1.0f,0.0f);
     GL11.glVertex3f( 1.0f,-1.0f,-1.0f);
     GL11.glVertex3f(-1.0f,-1.0f,-1.0f);
     GL11.glVertex3f(-1.0f, 1.0f,-1.0f);
     GL11.glVertex3f( 1.0f, 1.0f,-1.0f);
     GL11.glColor3f(0.0f,0.0f,1.0f);
     GL11.glVertex3f(-1.0f, 1.0f, 1.0f);
     GL11.glVertex3f(-1.0f, 1.0f,-1.0f);
     GL11.glVertex3f(-1.0f,-1.0f,-1.0f);
     GL11.glVertex3f(-1.0f,-1.0f, 1.0f);
     GL11.glColor3f(1.0f,0.0f,1.0f);
     GL11.glVertex3f( 1.0f, 1.0f,-1.0f);
     GL11.glVertex3f( 1.0f, 1.0f, 1.0f);
     GL11.glVertex3f( 1.0f,-1.0f, 1.0f);
     GL11.glVertex3f( 1.0f,-1.0f,-1.0f);
 GL11.glEnd();    

}

private void update() {
    if (Keyboard.isKeyDown(Keyboard.KEY_UP)) {
        viewx -= 0.1f*(float)Math.sin(Math.toRadians(angle));
        viewy -= 0.1f*(float)Math.cos(Math.toRadians(angle));
    }

    if (Keyboard.isKeyDown(Keyboard.KEY_DOWN)) {
        viewx += 0.1f*(float)Math.sin(Math.toRadians(angle));
        viewy += 0.1f*(float)Math.cos(Math.toRadians(angle));
    }
    if (Keyboard.isKeyDown(Keyboard.KEY_RIGHT)) {
        viewx+= 0.1f*(float)Math.sin(Math.toRadians(angle-90));
        viewy+=0.1f*(float)Math.cos(Math.toRadians(angle-90));
    }

    if (Keyboard.isKeyDown(Keyboard.KEY_LEFT)) {
        viewx+= 0.1f*(float)Math.sin(Math.toRadians(angle+90));
        viewy+=0.1f*(float)Math.cos(Math.toRadians(angle+90));
    }

    if (Keyboard.isKeyDown(Keyboard.KEY_Q)) {
         angle += 1;
    }


    if (Keyboard.isKeyDown(Keyboard.KEY_E)) {
        angle -= 1;
    }

    glLoadIdentity();
    glRotatef (angle, 0, 0, 1);
    glTranslated(viewx, viewy, -20);

    GL11.glBegin(GL11.GL_QUADS);    
    GL11.glColor3f(1.0f,1.0f,0.0f);           
    GL11.glVertex3f( -viewx-0.2f, -viewy-0.2f,0);        
    GL11.glVertex3f(-viewx+0.2f, -viewy-0.2f, 0);        
    GL11.glVertex3f(-viewx+0.2f, -viewy+0.2f, 0);
    GL11.glVertex3f( -viewx-0.2f, -viewy+0.2f, 0);  
    glEnd();       

}
}

Answer 1

该游戏似乎使用了正交投影 - 请注意离相机越远的东西并没有变小。这就是为什么线条的方向不依赖于相机位置的原因。

这张图片的左半部分显示了用透视投影渲染的板条箱网格。右半部分显示了使用正交投影渲染的相同网格。

请注意，通过正交投影，所有板条箱看起来都一样，无论它们的位置如何，也无论它们与相机的距离如何 - 只有它们的方向很重要。

在 OpenGL fixed-function 管道中，您可以使用 glOrtho 设置正交投影。如果你使用的是可编程流水线，那么就看你的具体程序了；通常，您需要在 fo

中使用投影矩阵

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