1 前言

​ 本文主要介绍使用 OpenGL ES 绘制立方体,读者如果对 OpenGL ES 不太熟悉,请回顾以下内容:

​ 在绘制立方体的过程中,主要用到了 MVP (Model View Projection)矩阵变换。

  • Model:模型变换,施加在模型上的空间变换,包含平移变换(translateM)、旋转变换(rotateM)、对称变换(transposeM)、缩放变换(scaleM);
  • View:观测变换,施加在观测点上的变换,用于调整观测点位置、观测朝向、观测正方向;
  • Projection:透视变换,施加在视觉上的变换,用于调整模型的透视效果(如:矩形的透视效果是梯形)。

​ 上述变换依次叠加,得到一个总的变换矩阵,即 MVP 变换矩阵,mvpMatrix = projectionMatrix * viewMatrix * modelMatrix,MVP 变换作用到模型的原始坐标矩阵上,得到的最终坐标矩阵即为用户观测到的模型状态。MVP 矩阵变换原理见→MVP矩阵变换

​ 本文完整代码资源见→【OpenGL ES】绘制立方体

​ 项目目录如下:

img

2 案例

​ MainActivity.java

package com.zhyan8.cube;

import android.opengl.GLSurfaceView;
import android.os.Bundle;
import androidx.appcompat.app.AppCompatActivity;

public class MainActivity extends AppCompatActivity {
    private GLSurfaceView mGlSurfaceView;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        mGlSurfaceView = new MyGLSurfaceView(this);
        setContentView(mGlSurfaceView);
        mGlSurfaceView.setRenderer(new MyRender(this));
    }

    @Override
    protected void onResume() {
        super.onResume();
        mGlSurfaceView.onResume();
    }

    @Override
    protected void onPause() {
        super.onPause();
        mGlSurfaceView.onPause();
    }
}

​ MyGLSurfaceView.java

package com.zhyan8.cube;

import android.content.Context;
import android.opengl.GLSurfaceView;
import android.util.AttributeSet;

public class MyGLSurfaceView extends GLSurfaceView {
    public MyGLSurfaceView(Context context) {
        super(context);
        setEGLContextClientVersion(3);
    }

    public MyGLSurfaceView(Context context, AttributeSet attrs) {
        super(context, attrs);
        setEGLContextClientVersion(3);
    }
}

​ MyRender.java

package com.zhyan8.cube;

import android.content.Context;
import android.opengl.GLES30;
import android.opengl.GLSurfaceView;
import java.nio.ByteBuffer;
import java.nio.FloatBuffer;
import javax.microedition.khronos.egl.EGLConfig;
import javax.microedition.khronos.opengles.GL10;

public class MyRender implements GLSurfaceView.Renderer {
    private FloatBuffer vertexBuffer;
    private FloatBuffer colorBuffer;
    private ByteBuffer indexBuffer;
    private GLUtils mGLUtils;
    private int mProgramId;
    private float mRatio;

    public MyRender(Context context) {
        mGLUtils = new GLUtils(context);
    }

    @Override
    public void onSurfaceCreated(GL10 gl, EGLConfig eglConfig) {
        //设置背景颜色
        GLES30.glClearColor(0.1f, 0.2f, 0.3f, 0.4f);
        //启动深度测试
        gl.glEnable(GLES30.GL_DEPTH_TEST);
        //编译着色器
        final int vertexShaderId = mGLUtils.compileShader(GLES30.GL_VERTEX_SHADER, R.raw.vertex_shader);
        final int fragmentShaderId = mGLUtils.compileShader(GLES30.GL_FRAGMENT_SHADER, R.raw.fragment_shader);
        //链接程序片段
        mProgramId = mGLUtils.linkProgram(vertexShaderId, fragmentShaderId);
        GLES30.glUseProgram(mProgramId);
    }

    @Override
    public void onSurfaceChanged(GL10 gl, int width, int height) {
        //设置视图窗口
        GLES30.glViewport(0, 0, width, height);
        getFloatBuffer();
        mRatio = 1.0f * width / height;
    }

    @Override
    public void onDrawFrame(GL10 gl) {
        //将颜色缓冲区设置为预设的颜色
        GLES30.glClear(GLES30.GL_COLOR_BUFFER_BIT | GLES30.GL_DEPTH_BUFFER_BIT);
        mGLUtils.transform(mProgramId, mRatio); //计算MVP变换矩阵
        //启用顶点的数组句柄
        GLES30.glEnableVertexAttribArray(0);
        GLES30.glEnableVertexAttribArray(1);
        //准备顶点坐标和颜色数据
        GLES30.glVertexAttribPointer(0, 3, GLES30.GL_FLOAT, false, 0, vertexBuffer);
        GLES30.glVertexAttribPointer(1, 4, GLES30.GL_FLOAT, false, 0, colorBuffer);
        //绘制正方体的表面(6个面,每面2个三角形,每个三角形3个顶点)
        gl.glDrawElements(GLES30.GL_TRIANGLES, 6 * 2 * 3, GLES30.GL_UNSIGNED_BYTE, indexBuffer);
        //禁止顶点数组句柄
        GLES30.glDisableVertexAttribArray(0);
        GLES30.glDisableVertexAttribArray(1);
    }

    private void getFloatBuffer() {
        float r = 1.0f;
        float[] vertex = new float[] {
            r, r, r, //0
            -r, r, r, //1
            -r, -r, r, //2
            r, -r, r, //3
            r, r, -r, //4
            -r, r, -r, //5
            -r, -r, -r, //6
            r, -r, -r //7
        };
        byte[] index = new byte[] {
            0, 2, 1, 0, 2, 3, //前面
            0, 5, 1, 0, 5, 4, //上面
            0, 7, 3, 0, 7, 4, //右面
            6, 4, 5, 6, 4, 7, //后面
            6, 3, 2, 6, 3, 7, //下面
            6, 1, 2, 6, 1, 5 //左面
        };
        float c = 1.0f;
        float[] color = new float[] {
            c, c, c, 1,
            0, c, c, 1,
            0, 0, c, 1,
            c, 0, c, 1,
            c, c, 0, 1,
            0, c, 0, 1,
            0, 0, 0, 1,
            c, 0, 0, 1
        };
        vertexBuffer = mGLUtils.getFloatBuffer(vertex);
        indexBuffer = mGLUtils.getByteBuffer(index);
        colorBuffer = mGLUtils.getFloatBuffer(color);
    }
}

​ GLUtils.java

package com.zhyan8.cube;

import android.content.Context;
import android.opengl.GLES30;
import android.opengl.Matrix;
import java.io.BufferedReader;
import java.io.InputStream;
import java.io.InputStreamReader;
import java.nio.ByteBuffer;
import java.nio.ByteOrder;
import java.nio.FloatBuffer;

public class GLUtils {
    private Context mContext;
    private int mRotateAgree = 0;

    public GLUtils(Context context) {
        mContext = context;
    }

    public FloatBuffer getFloatBuffer(float[] floatArr) {
        FloatBuffer fb = ByteBuffer.allocateDirect(floatArr.length * Float.BYTES)
            .order(ByteOrder.nativeOrder())
            .asFloatBuffer();
        fb.put(floatArr);
        fb.position(0);
        return fb;
    }

    public ByteBuffer getByteBuffer(byte[] byteArr) {
        ByteBuffer bb = ByteBuffer.allocateDirect(byteArr.length * Byte.BYTES)
                .order(ByteOrder.nativeOrder());
        bb.put(byteArr);
        bb.position(0);
        return bb;
    }

    //通过代码片段编译着色器
    public int compileShader(int type, String shaderCode){
        int shader = GLES30.glCreateShader(type);
        GLES30.glShaderSource(shader, shaderCode);
        GLES30.glCompileShader(shader);
        return shader;
    }

    //通过外部资源编译着色器
    public int compileShader(int type, int shaderId){
        String shaderCode = readShaderFromResource(shaderId);
        return compileShader(type, shaderCode);
    }

    //链接到着色器
    public int linkProgram(int vertexShaderId, int fragmentShaderId) {
        final int programId = GLES30.glCreateProgram();
        //将顶点着色器加入到程序
        GLES30.glAttachShader(programId, vertexShaderId);
        //将片元着色器加入到程序
        GLES30.glAttachShader(programId, fragmentShaderId);
        //链接着色器程序
        GLES30.glLinkProgram(programId);
        return programId;
    }

    //从shader文件读出字符串
    private String readShaderFromResource(int shaderId) {
        InputStream is = mContext.getResources().openRawResource(shaderId);
        BufferedReader br = new BufferedReader(new InputStreamReader(is));
        String line;
        StringBuilder sb = new StringBuilder();
        try {
            while ((line = br.readLine()) != null) {
                sb.append(line);
                sb.append("\n");
            }
            br.close();
        } catch (Exception e) {
            e.printStackTrace();
        }
        return sb.toString();
    }

    //计算MVP变换矩阵
    public void transform(int programId, float ratio) {
        //初始化modelMatrix, viewMatrix, projectionMatrix
        float[] modelMatrix = getIdentityMatrix(16, 0); //模型变换矩阵
        float[] viewMatrix = getIdentityMatrix(16, 0); //观测变换矩阵
        float[] projectionMatrix = getIdentityMatrix(16, 0); //投影变换矩阵
        //获取modelMatrix, viewMatrix, projectionMatrix
        mRotateAgree = (mRotateAgree + 2) % 360;
        Matrix.rotateM(modelMatrix, 0, mRotateAgree, 1, 1, 1); //获取模型旋转变换矩阵
        Matrix.setLookAtM(viewMatrix, 0, 0, 5, 10, 0, 0, 0, 0, 1, 0); //获取观测变换矩阵
        Matrix.frustumM(projectionMatrix, 0, -ratio, ratio, -1, 1, 3, 20); //获取投影变换矩阵
        //计算MVP变换矩阵: mvpMatrix = projectionMatrix * viewMatrix * modelMatrix
        float[] mvpMatrix = new float[16];
        Matrix.multiplyMM(mvpMatrix, 0, viewMatrix, 0, modelMatrix, 0);
        Matrix.multiplyMM(mvpMatrix, 0, projectionMatrix, 0, mvpMatrix, 0);
        //设置MVP变换矩阵
        int mvpMatrixHandle = GLES30.glGetUniformLocation(programId, "mvpMatrix");
        GLES30.glUniformMatrix4fv(mvpMatrixHandle, 1, false, mvpMatrix, 0);
    }

    private float[] getIdentityMatrix(int size, int offset) {
        float[] matrix = new float[size];
        Matrix.setIdentityM(matrix, offset);
        return matrix;
    }
}

​ vertex_shader.glsl

#version 300 es
layout (location = 0) in vec4 vPosition;
layout (location = 1) in vec4 aColor;
uniform mat4 mvpMatrix;
out vec4 vColor;
void main() {
     gl_Position  = mvpMatrix * vPosition;
     vColor = aColor;
}

​ 顶点着色器的作用:进行矩阵变换位置、根据光照公式计算顶点颜⾊⽣成 / 变换纹理坐标,并且把位置和纹理坐标发送到片元着色器。

​ 顶点着色器中,如果没有指定默认精度,则 int 和 float 的默认精度都为 highp。

​ fragment_shader.glsl

#version 300 es
precision mediump float; //声明float型变量的精度为mediump
in vec4 vColor;
out vec4 fragColor;
void main() {
     fragColor = vColor;
}

​ 片元着色器的作用:处理经光栅化阶段生成的每个片元,计算每个像素的颜色和透明度。

​ 在片元着色器中,浮点值没有默认的精度值,每个着色器必须声明一个默认的 float 精度。

运行结果:

img

​ 声明:本文转自【OpenGL ES】绘制正方形