OpenGL ES在安卓上画一个正方形

// 初始化OpenGL ES环境
GLSurfaceView glSurfaceView = new GLSurfaceView(context);
glSurfaceView.setEGLContextClientVersion(2);
glSurfaceView.setRenderer(new MyRenderer());

// 创建顶点和片段着色器
String vertexShaderCode =
    "attribute vec4 vPosition;" +
    "void main() {" +
    "  gl_Position = vPosition;" +
    "}";
String fragmentShaderCode =
    "precision mediump float;" +
    "void main() {" +
    "  gl_FragColor = vec4(1.0, 0.0, 0.0, 1.0);" +
    "}";

// 定义顶点数据
float[] vertices = {
    -0.5f, 0.5f, 0.0f,  // 左上角
    -0.5f, -0.5f, 0.0f, // 左下角
    0.5f, -0.5f, 0.0f,  // 右下角
    0.5f, 0.5f, 0.0f    // 右上角
};

// 加载着色器和顶点数据
int vertexShader = loadShader(GLES20.GL_VERTEX_SHADER, vertexShaderCode);
int fragmentShader = loadShader(GLES20.GL_FRAGMENT_SHADER, fragmentShaderCode);
int program = createProgram(vertexShader, fragmentShader);
int positionHandle = GLES20.glGetAttribLocation(program, "vPosition");
FloatBuffer vertexBuffer = ByteBuffer.allocateDirect(vertices.length * 4)
    .order(ByteOrder.nativeOrder())
    .asFloatBuffer()
    .put(vertices);
vertexBuffer.position(0);

// 绘制正方形
GLES20.glUseProgram(program);
GLES20.glEnableVertexAttribArray(positionHandle);
GLES20.glVertexAttribPointer(positionHandle, 3, GLES20.GL_FLOAT, false, 12, vertexBuffer);
GLES20.glDrawArrays(GLES20.GL_TRIANGLE_FAN, 0, 4);
GLES20.glDisableVertexAttribArray(positionHandle);