<uses-feature android:glEsVersion="0x00020000" android:required="true" />

private class SimpleEGLConfigChooser extends ComponentSizeChooser {
    public SimpleEGLConfigChooser(boolean withDepthBuffer) {
        super(8, 8, 8, 0, withDepthBuffer ? 16 : 0, 0);
    }
}

// 設(shè)置默認(rèn)EGLConfig的深度緩沖，true則為16位的深度緩沖
setEGLConfigChooser(boolean needDepth)
// 指定自定義的EGLConfigChooser
setEGLConfigChooser(android.opengl.GLSurfaceView.EGLConfigChooser configChooser)
// 指定各個(gè)分量的值
public void setEGLConfigChooser(int redSize, int greenSize, int blueSize,
            int alphaSize, int depthSize, int stencilSize)

// 設(shè)置渲染器
public void setRenderer(Renderer renderer)
// 設(shè)置渲染模式，僅在setRenderer之后調(diào)用生效
public void setRenderMode(int renderMode)

// DEBUG_CHECK_GL_ERROR：每次GL調(diào)用都會(huì)檢查，如果出現(xiàn)glError則會(huì)拋出異常
// DEBUG_LOG_GL_CALLS：以TAG為GLSurfaceView將日志記錄在verbose級(jí)別的日志中
setDebugFlags(int debugFlags)
// 用于調(diào)試跟蹤代碼，可自定義GLWrapper包裝GL接口并返回GL接口，可在
setGLWrapper(android.opengl.GLSurfaceView.GLWrapper glWrapper)

// 給GLSurfaceView設(shè)置渲染器對(duì)象Renderer
public void setRenderer(Renderer renderer)
// 設(shè)置渲染模式，僅在setRenderer之后調(diào)用生效
public void setRenderMode(int renderMode)

public class GLES20Renderer implements Renderer {
    private static final String TAG = GLES20Renderer.class.getSimpleName();
    public void onSurfaceCreated(GL10 gl, EGLConfig config) {
        Log.i(TAG, "onSurfaceCreated");
        GLES20.glClearColor(0.0f, 0.0f, 1.0f, 1);
    }
    public void onSurfaceChanged(GL10 gl, int width, int height) {
        Log.i(TAG, "onSurfaceChanged");
        GLES20.glViewport(0, 0, width, height);
    }
    public void onDrawFrame(GL10 gl) {
        Log.i(TAG, "onDrawFrame");
        GLES20.glClear(GLES20.GL_COLOR_BUFFER_BIT | GLES20.GL_DEPTH_BUFFER_BIT);
    }
}

// Triangle
class Triangle(context: Context) {
    companion object {
        // 坐標(biāo)數(shù)組中每個(gè)頂點(diǎn)的坐標(biāo)數(shù)
        private const val COORDINATE_PER_VERTEX = 3
    }
    private var programHandle: Int = 0
    private var positionHandle: Int = 0
    private var colorHandler: Int = 0
    private var vPMatrixHandle: Int = 0
    private var vertexStride = COORDINATE_PER_VERTEX * 4
    // 三角形的三條邊
    private var triangleCoordinate = floatArrayOf(     // 逆時(shí)針的順序的三條邊
        0.0f, 0.5f, 0.0f,      // top
        -0.5f, -0.5f, 0.0f,    // bottom left
        0.5f, -0.5f, 0.0f      // bottom right
    )
    // 顏色數(shù)組
    private val color = floatArrayOf(0.63671875f, 0.76953125f, 0.22265625f, 1.0f)
    private var vertexBuffer: FloatBuffer =
        // (number of coordinate values * 4 bytes per float)
        ByteBuffer.allocateDirect(triangleCoordinate.size * 4).run {
            // ByteBuffer使用本機(jī)字節(jié)序
            this.order(ByteOrder.nativeOrder())
            // ByteBuffer to FloatBuffer
            this.asFloatBuffer().apply {
                put(triangleCoordinate)
                position(0)
            }
        }
    init {
        // read shader sourceCode
        val vertexShaderCode = GLUtil.readShaderSourceCodeFromRaw(context, R.raw.vertex_shader_triangle_default)
        val fragmentShaderCode =
            GLUtil.readShaderSourceCodeFromRaw(context, R.raw.fragment_shader_triangle)
        if (vertexShaderCode.isNullOrEmpty() || fragmentShaderCode.isNullOrEmpty()) {
            throw RuntimeException("vertexShaderCode or fragmentShaderCode is null or empty")
        }
        // compile shader
        val vertexShaderHandler = GLUtil.compileShader(GLES20.GL_VERTEX_SHADER, vertexShaderCode)
        val fragmentShaderHandler =
            GLUtil.compileShader(GLES20.GL_FRAGMENT_SHADER, fragmentShaderCode)
        // create and link program
        programHandle = GLUtil.createAndLinkProgram(vertexShaderHandler, fragmentShaderHandler)
    }
    /**
 	 *  繪制方法
 	 */
    fun draw(mvpMatrix: FloatArray) {
        GLES20.glUseProgram(programHandle)
        // 獲取attribute變量的地址索引
        // get handle to vertex shader's vPosition member
        positionHandle = GLES20.glGetAttribLocation(programHandle, "vPosition").also {
            // enable vertex attribute，默認(rèn)是disable
            GLES20.glEnableVertexAttribArray(it)
            GLES20.glVertexAttribPointer(
                it, // 著色器中第一個(gè)頂點(diǎn)屬性的位置
                COORDINATE_PER_VERTEX,
                GLES20.GL_FLOAT,
                false,
                vertexStride, // 連續(xù)的頂點(diǎn)屬性組之間的間隔
                vertexBuffer
            )
        }
        // get handle to fragment shader's vColor member
        colorHandler = GLES20.glGetUniformLocation(programHandle, "vColor").also {
            GLES20.glUniform4fv(it, 1, color, 0)
        }
        // draw triangle
        GLES20.glDrawArrays(GLES20.GL_TRIANGLES, 0, triangleCoordinate.size / COORDINATE_PER_VERTEX)
        GLES20.glDisableVertexAttribArray(positionHandle)
    }
}

// 渲染器實(shí)現(xiàn)
class MRenderer(private var context: Context) : GLSurfaceView.Renderer {
    private val tag = MRenderer::class.java.simpleName
    private lateinit var triangle: Triangle
    private val vPMatrix = FloatArray(16) // 模型視圖投影矩陣
    private val projectionMatrix = FloatArray(16)
    private val viewMatrix = FloatArray(16)
    override fun onSurfaceCreated(gl: GL10?, config: EGLConfig?) {
        // 創(chuàng)建Surface時(shí)調(diào)用，在渲染開始時(shí)調(diào)用，用來創(chuàng)建渲染開始時(shí)需要的資源
        Log.d(tag, "onSurfaceCreated")
        triangle = Triangle(context)
    }
    override fun onSurfaceChanged(gl: GL10?, width: Int, height: Int) {
        // Surface改變大小時(shí)調(diào)用，設(shè)置視口
        Log.d(tag, "onSurfaceChanged")
        GLES20.glViewport(0, 0, width, height)
    }
    override fun onDrawFrame(gl: GL10?) {
        // 繪制當(dāng)前frame，用于渲染處理具體的內(nèi)容
        Log.d(tag, "onDrawFrame")
        triangle.draw(vPMatrix)
    }
}