JOGL 3D桨轮

JOGL（Java Binding for the OpenGL）是Java平台上对OpenGL的绑定库。JOGL允许Java程序在跨平台开发过程中调用OpenGL标准，从而可以获得高质量的3D图形渲染效果。

本篇文章将介绍使用JOGL绘制3D桨轮的基本步骤，以及如何在Java中实现旋转、平移和缩放等操作。

准备工作

在开始之前，需要确保Java已安装并配置了JOGL库。可以通过以下代码片段，检查是否已经配置：

import javax.media.opengl.GL;
import javax.media.opengl.GLAutoDrawable;
import javax.media.opengl.GLCapabilities;
import javax.media.opengl.GLEventListener;
import javax.media.opengl.GLProfile;
import javax.media.opengl.awt.GLCanvas;
import javax.swing.JFrame;

public class JOGLTest {
    public static void main(String[] args) {
        GLProfile profile = GLProfile.get(GLProfile.GL2);
        GLCapabilities capabilities = new GLCapabilities(profile);
        GLCanvas canvas = new GLCanvas(capabilities);

        JFrame frame = new JFrame("JOGL Test");
        frame.setSize(400, 400);
        frame.getContentPane().add(canvas);
        frame.setVisible(true);
    }
}

运行以上代码，如果出现OpenGL窗口，则表明JOGL配置成功。

绘制桨轮

以下代码片段将展示如何使用JOGL绘制3D桨轮：

import javax.media.opengl.GL;
import javax.media.opengl.GLAutoDrawable;
import javax.media.opengl.GLCapabilities;
import javax.media.opengl.GLProfile;
import javax.media.opengl.awt.GLCanvas;
import javax.media.opengl.GLEventListener;
import javax.swing.JFrame;

public class JOGLWheel implements GLEventListener {
    private GLCanvas canvas;
    private double rotateX = 0;
    private double rotateY = 0;
    private double rotateZ = 0;

    public JOGLWheel(GLCanvas canvas) {
        this.canvas = canvas;
        canvas.addGLEventListener(this);
    }

    @Override
    public void init(GLAutoDrawable drawable) {
        GL gl = drawable.getGL();
        gl.glClearColor(1.0f, 1.0f, 1.0f, 1.0f);
        gl.glEnable(GL.GL_DEPTH_TEST);
    }

    @Override
    public void display(GLAutoDrawable drawable) {
        GL gl = drawable.getGL();
        gl.glClear(GL.GL_COLOR_BUFFER_BIT | GL.GL_DEPTH_BUFFER_BIT);
        gl.glMatrixMode(GL.GL_MODELVIEW);
        gl.glLoadIdentity();
        gl.glTranslatef(0, 0, -10f);
        gl.glRotatef((float)rotateX, 1, 0, 0);
        gl.glRotatef((float)rotateY, 0, 1, 0);
        gl.glRotatef((float)rotateZ, 0, 0, 1);
        drawWheel(gl);
        rotateX += 1.5;
        rotateY += 1.5;
        rotateZ += 1.5;
    }

    @Override
    public void reshape(GLAutoDrawable drawable, int x, int y, int width, int height) {
        GL gl = drawable.getGL();
        gl.glViewport(0, 0, width, height);
        gl.glMatrixMode(GL.GL_PROJECTION);
        gl.glLoadIdentity();
        float aspect = (float)width / (float)height;
        float fovy = 60.0f;
        float zNear = 0.1f;
        float zFar = 100.0f;
        float top = (float)Math.tan(Math.toRadians(fovy * 0.5)) * zNear;
        float bottom = -top;
        float left = aspect * bottom;
        float right = aspect * top;
        gl.glFrustum(left, right, bottom, top, zNear, zFar);
    }

    private void drawWheel(GL gl) {
        int spokes = 8;
        float outerRadius = 2f;
        float innerRadius = 1.5f;
        float thickness = 0.5f;
        float spokeWidth = thickness * 0.2f;
        float spokeInnerRadius = innerRadius - thickness * 0.5f;
        float spokeOuterRadius = outerRadius + thickness * 0.5f;

        for (int i = 0; i < spokes; i++) {
            float angle = i * 360f / spokes;
            float x1 = outerRadius * (float)Math.cos(Math.toRadians(angle));
            float y1 = outerRadius * (float)Math.sin(Math.toRadians(angle));
            float x2 = innerRadius * (float)Math.cos(Math.toRadians(angle));
            float y2 = innerRadius * (float)Math.sin(Math.toRadians(angle));
            float x3 = innerRadius * (float)Math.cos(Math.toRadians(angle + spokeWidth));
            float y3 = innerRadius * (float)Math.sin(Math.toRadians(angle + spokeWidth));
            float x4 = outerRadius * (float)Math.cos(Math.toRadians(angle + spokeWidth));
            float y4 = outerRadius * (float)Math.sin(Math.toRadians(angle + spokeWidth));

            gl.glBegin(GL.GL_QUAD_STRIP);
            gl.glColor3f(0.0f, 0.0f, 0.0f);
            for (int j = 0; j <= 10; j++) {
                float s = j / 10f;
                float cx = x2 + (x1 - x2) * s;
                float cy = y2 + (y1 - y2) * s;
                float ix = x3 + (x2 - x3) * s;
                float iy = y3 + (y2 - y3) * s;
                float ox = x4 + (x1 - x4) * s;
                float oy = y4 + (y1 - y4) * s;

                gl.glVertex3f(cx, cy, 0);
                gl.glVertex3f(ox, oy, 0);
                gl.glVertex3f(ix, iy, -thickness);
                gl.glVertex3f(ix, iy, -thickness);
            }
            gl.glEnd();

            gl.glBegin(GL.GL_TRIANGLE_FAN);
            gl.glColor3f(1.0f, 1.0f, 1.0f);
            for (int j = 0; j <= 10; j++) {
                float s = j / 10f;
                float ix = x3 + (x2 - x3) * s;
                float iy = y3 + (y2 - y3) * s;
                gl.glVertex3f(ix, iy, -thickness);
            }
            gl.glEnd();

            gl.glBegin(GL.GL_QUAD_STRIP);
            gl.glColor3f(0.0f, 0.0f, 0.0f);
            for (int j = 0; j <= 10; j++) {
                float s = j / 10f;
                float cx = x2 + (x1 - x2) * s;
                float cy = y2 + (y1 - y2) * s;
                float ix = x3 + (x4 - x3) * s;
                float iy = y3 + (y4 - y3) * s;
                float ox = x1 + (x4 - x1) * s;
                float oy = y1 + (y4 - y1) * s;

                gl.glVertex3f(cx, cy, -thickness);
                gl.glVertex3f(ox, oy, -thickness);
                gl.glVertex3f(ix, iy, -thickness*2);
                gl.glVertex3f(ix, iy, -thickness*2);
            }
            gl.glEnd();

            gl.glBegin(GL.GL_TRIANGLE_FAN);
            gl.glColor3f(1.0f, 1.0f, 1.0f);
            for (int j = 0; j <= 10; j++) {
                float s = j / 10f;
                float ix = x3 + (x4 - x3) * s;
                float iy = y3 + (y4 - y3) * s;
                gl.glVertex3f(ix, iy, -thickness*2);
            }
            gl.glEnd();

            gl.glBegin(GL.GL_QUAD_STRIP);
            gl.glColor3f(0.0f, 0.0f, 0.0f);
            for (int j = 0; j <= 10; j++) {
                float s = j / 10f;
                float cx = x2 + (x1 - x2) * s;
                float cy = y2 + (y1 - y2) * s;
                float ix = x3 + (x2 - x3) * s;
                float iy = y3 + (y2 - y3) * s;
                float ox = x4 + (x1 - x4) * s;
                float oy = y4 + (y1 - y4) * s;

                gl.glVertex3f(cx, cy, -thickness*2);
                gl.glVertex3f(ox, oy, -thickness*2);
                gl.glVertex3f(ix, iy, -thickness*3);
                gl.glVertex3f(ix, iy, -thickness*3);
            }
            gl.glEnd();

            gl.glBegin(GL.GL_TRIANGLE_FAN);
            gl.glColor3f(1.0f, 1.0f, 1.0f);
            for (int j = 0; j <= 10; j++) {
                float s = j / 10f;
                float ix = x3 + (x2 - x3) * s;
                float iy = y3 + (y2 - y3) * s;
                gl.glVertex3f(ix, iy, -thickness*3);
            }
            gl.glEnd();
        }
    }
}

以上代码定义了一个JOGLWheel类，实现了GLEventListener接口。在display函数中，使用OpenGL绘制了一个3D桨轮。在reshape函数中，计算了视角矩阵。

在main函数中，通过以下代码，启动绘制：

public class JOGLTest {
    public static void main(String[] args) {
        GLProfile profile = GLProfile.get(GLProfile.GL2);
        GLCapabilities capabilities = new GLCapabilities(profile);
        GLCanvas canvas = new GLCanvas(capabilities);

        JFrame frame = new JFrame("JOGL Test");
        frame.setSize(400, 400);
        frame.getContentPane().add(canvas);
        frame.setVisible(true);

        JOGLWheel wheel = new JOGLWheel(canvas);
        FPSAnimator animator = new FPSAnimator(canvas, 60, true);
        animator.start();
    }
}

旋转、平移和缩放

要在Java中实现3D桨轮的旋转、平移和缩放等操作，可以通过修改display函数中的代码实现。例如，要实现使桨轮旋转，可以将以下代码添加到display函数中：

gl.glRotatef(rotateX, 1, 0, 0);
gl.glRotatef(rotateY, 0, 1, 0);
gl.glRotatef(rotateZ, 0, 0, 1);
rotateX += 1.5;
rotateY += 1.5;
rotateZ += 1.5;

这里，rotateX、rotateY和rotateZ依次表示绕X、Y和Z轴旋转的角度，每次增加1.5度。

类似地，要实现平移和缩放，可以使用glTranslatef和glScalef函数，例如：

gl.glTranslatef(0, 0, -10f);
gl.glScalef(0.5f, 0.5f, 0.5f);

这里，将桨轮沿Z轴平移10个单位，并将桨轮缩小到原来的1/2。

结语

本文介绍了使用JOGL绘制3D桨轮的基本步骤，以及如何在Java中实现旋转、平移和缩放等操作。除了本文中展示的代码，JOGL还提供了许多其他的OpenGL函数和工具，开发者可以根据自己的需求进行扩展和优化。