【libGDX】Mesh立方体贴图（6张图）

1 前言

本文通过一个立方体贴图的例子，讲解三维纹理贴图的应用，案例中使用 6 张不同的图片给立方体贴图，图片如下。

读者如果对 libGDX 不太熟悉，请回顾以下内容。

使用Mesh绘制三角形
使用Mesh绘制矩形
使用Mesh绘制圆形
使用Mesh绘制立方体
Mesh纹理贴图

2 立方体贴图

本节将使用 Mesh、ShaderProgram、Shader 实现立方体贴图，OpenGL ES 的实现见博客 → 立方体贴图（6张图），本节完整代码资源见 → libGDX Mesh立方体贴图（6张图）。

DesktopLauncher.java

package com.zhyan8.game;

import com.badlogic.gdx.backends.lwjgl3.Lwjgl3Application;
import com.badlogic.gdx.backends.lwjgl3.Lwjgl3ApplicationConfiguration;

public class DesktopLauncher {
	public static void main (String[] arg) {
		Lwjgl3ApplicationConfiguration config = new Lwjgl3ApplicationConfiguration();
		config.setForegroundFPS(60);
		config.setTitle("CubeChartlet");
		new Lwjgl3Application(new CubeChartlet(), config);
	}
}

CubeChartlet.java

package com.zhyan8.game;

import com.badlogic.gdx.ApplicationAdapter;
import com.badlogic.gdx.Gdx;
import com.badlogic.gdx.graphics.GL30;
import com.badlogic.gdx.graphics.Mesh;
import com.badlogic.gdx.graphics.PerspectiveCamera;
import com.badlogic.gdx.graphics.Texture;
import com.badlogic.gdx.graphics.VertexAttribute;
import com.badlogic.gdx.graphics.VertexAttributes.Usage;
import com.badlogic.gdx.graphics.glutils.ShaderProgram;
import com.badlogic.gdx.math.Matrix4;
import com.badlogic.gdx.math.Vector3;

public class CubeChartlet extends ApplicationAdapter {
	private PerspectiveCamera mCamera;
	private ShaderProgram mShaderProgram;
	private Mesh mMesh;
	private Texture[] mTextures;
	private Vector3 mRotateAxis; // 旋转轴
	private int mRotateAgree = 0; // 旋转角度
	Matrix4 mModelMatrix; // 模型变换矩阵

	@Override
	public void create() {
		initCamera();
		initShader();
		initMesh();
		initTextures();
		mRotateAxis = new Vector3(0.5f, 1f, 1f);
		mModelMatrix = new Matrix4();
	}

	@Override
	public void render() {
		Gdx.gl.glClearColor(0.455f, 0.725f, 1.0f, 1.0f);
		Gdx.gl.glClear(GL30.GL_COLOR_BUFFER_BIT | GL30.GL_DEPTH_BUFFER_BIT);
		Gdx.gl.glEnable(GL30.GL_DEPTH_TEST);
		mShaderProgram.bind();
		transform();
		renderCube();
	}

	@Override
	public void dispose() {
		mShaderProgram.dispose();
		mMesh.dispose();
	}

	private void renderCube() {
		for (int i = 0; i < mTextures.length; i++) { // 给每个面都贴图
			// mShaderProgram.setUniformi("u_texture", 0); // 设置纹理单元
			mTextures[i].bind(0);
			mMesh.render(mShaderProgram, GL30.GL_TRIANGLE_FAN, i * 4, 4);
		}
	}

	private void initCamera() { // 初始化相机
		mCamera = new PerspectiveCamera(67, Gdx.graphics.getWidth(), Gdx.graphics.getHeight());
		mCamera.near = 0.3f;
		mCamera.far = 1000f;
		mCamera.position.set(0f, 0f, 4f);
		mCamera.lookAt(0, 0, 0);
		mCamera.update();
	}

	private void initShader() { // 初始化着色器程序
		String vertex = Gdx.files.internal("shaders/square_chartlet_vertex.glsl").readString();
		String fragment = Gdx.files.internal("shaders/square_chartlet_fragment.glsl").readString();
		mShaderProgram = new ShaderProgram(vertex, fragment);
	}

	private void initMesh() { // 初始化网格
		float[] vertices = Model.vertices;
		short[] indices = Model.indices;
		VertexAttribute vertexPosition = new VertexAttribute(Usage.Position, 3, "a_position");
		VertexAttribute texCoords = new VertexAttribute(Usage.TextureCoordinates, 2, "a_texCoord0");
		mMesh = new Mesh(true, vertices.length / 5, indices.length, vertexPosition, texCoords);
		mMesh.setVertices(vertices);
		mMesh.setIndices(indices);
	}

	private void initTextures() {
		mTextures = new Texture[Model.texturePaths.length];
		for (int i = 0; i < mTextures.length; i++) {
			mTextures[i] = new Texture(Gdx.files.internal(Model.texturePaths[i]));
		}
	}

	private void transform() { // MVP矩阵变换
		mRotateAgree = (mRotateAgree + 2) % 360;
		mRotateAxis.x = mRotateAgree / 180f - 1;
		mRotateAxis.y = (float) Math.sin(mRotateAgree / 180f * Math.PI * 0.7f);
		mRotateAxis.z = (float) Math.cos(mRotateAgree / 180f * Math.PI * 0.5f);
		mModelMatrix.idt(); // 模型变换矩阵单位化
		mModelMatrix.rotate(mRotateAxis, mRotateAgree);
		Matrix4 mvpMatrix = mModelMatrix.mulLeft(mCamera.combined);
		mShaderProgram.setUniformMatrix("u_mvpTrans", mvpMatrix);
	}
}

Model.java

package com.zhyan8.game;

public class Model {
    private static float r = 1.0f;

    public static String[] texturePaths = new String[] {
            "textures/a1.png", "textures/a2.png", "textures/a3.png",
            "textures/a4.png", "textures/a5.png", "textures/a6.png"
    };

    public static float[] vertices = new float[] {
            // 前面
            r, r, r, 0f, 0f, // 0
            -r, r, r, 1f, 0f, // 1
            -r, -r, r, 1f, 1f, // 2
            r, -r, r, 0f, 1f, // 3
            // 后面
            r, r, -r, 0f, 0f, // 4
            -r, r, -r, 1f, 0f, // 5
            -r, -r, -r, 1f, 1f, // 6
            r, -r, -r, 0f, 1f, // 7
            // 上面
            r, r, r, 0f, 0f, // 8
            r, r, -r, 1f, 0f, // 9
            -r, r, -r, 1f, 1f, // 10
            -r, r, r, 0f, 1f, // 11
            // 下面
            r, -r, r, 0f, 0f, // 12
            r, -r, -r, 1f, 0f, // 13
            -r, -r, -r, 1f, 1f, // 14
            -r, -r, r, 0f, 1f, // 15
            // 右面
            r, r, r, 0f, 0f, // 16
            r, r, -r, 1f, 0f, // 17
            r, -r, -r, 1f, 1f, // 18
            r, -r, r, 0f, 1f, // 19
            // 左面
            -r, r, r, 0f, 0f, // 20
            -r, r, -r, 1f, 0f, // 21
            -r, -r, -r, 1f, 1f, // 22
            -r, -r, r, 0f, 1f // 23
    };

    public static short[] indices = new short[] {
            0, 1, 2, 3, // 前面
            4, 5, 6, 7, // 上面
            8, 9, 10, 11, // 右面
            12, 13, 14, 15, // 后面
            16, 17, 18, 19, // 下面
            20, 21, 22, 23 // 左面
    };
}

square_chartlet_vertex.glsl

#version 300 es

in vec3 a_position;
in vec2 a_texCoord0;

uniform mat4 u_mvpTrans; // MVP矩阵变换

out vec2 v_texCoord0;

void main() {
    gl_Position = u_mvpTrans * vec4(a_position, 1.0);
    v_texCoord0 = a_texCoord0;
}

square_chartlet_fragment.glsl

#version 300 es
precision mediump float; // 声明float型变量的精度为mediump

in vec2 v_texCoord0;

uniform sampler2D u_texture;

out vec4 fragColor;

void main() {
    fragColor = texture(u_texture, v_texCoord0);
}

运行效果如下。