Flutter OpenGL图形渲染插件flutter_opengl的使用

当然，下面是一个关于如何在Flutter中使用flutter_opengl插件进行OpenGL图形渲染的示例代码。这个示例将展示如何设置OpenGL上下文并绘制一些基本的图形。

首先，确保你已经在pubspec.yaml文件中添加了flutter_opengl依赖：

dependencies:
  flutter:
    sdk: flutter
  flutter_opengl: ^x.y.z  # 请替换为最新的版本号

然后，运行flutter pub get来获取依赖。

接下来，创建一个Flutter项目，并在lib目录下创建一个新的Dart文件，比如main.dart。在这个文件中，我们将设置OpenGL上下文并绘制一个简单的三角形。

import 'package:flutter/material.dart';
import 'package:flutter_opengl/flutter_opengl.dart';
import 'dart:typed_data';
import 'dart:ui' as ui;

void main() {
  runApp(MyApp());
}

class MyApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      home: Scaffold(
        appBar: AppBar(
          title: Text('Flutter OpenGL Example'),
        ),
        body: OpenGLWidget(),
      ),
    );
  }
}

class OpenGLWidget extends StatefulWidget {
  @override
  _OpenGLWidgetState createState() => _OpenGLWidgetState();
}

class _OpenGLWidgetState extends State<OpenGLWidget> {
  late OpenGLRenderer _renderer;

  @override
  void initState() {
    super.initState();
    _renderer = OpenGLRenderer();
  }

  @override
  Widget build(BuildContext context) {
    return Container(
      color: Colors.black,
      child: CustomPaint(
        painter: _OpenGLPainter(_renderer),
        size: Size(double.infinity, double.infinity),
      ),
    );
  }

  @override
  void dispose() {
    _renderer.dispose();
    super.dispose();
  }
}

class OpenGLRenderer {
  late ui.Window _window;
  late FlutterOpenGL _flutterOpenGL;

  OpenGLRenderer() {
    _window = ui.window;
    _flutterOpenGL = FlutterOpenGL(_window);

    // 设置视口大小
    _flutterOpenGL.glViewport(0, 0, _window.physicalSize.width.toInt(), _window.physicalSize.height.toInt());

    // 初始化OpenGL状态
    _initializeOpenGL();
  }

  void _initializeOpenGL() {
    // 启用深度测试
    _flutterOpenGL.glEnable(0x0B71); // GL_DEPTH_TEST

    // 设置清除颜色为黑色
    _flutterOpenGL.glClearColor(0.0, 0.0, 0.0, 1.0);

    // 创建着色器程序
    int vertexShader = _loadShader(GL_VERTEX_SHADER, vertexShaderSource);
    int fragmentShader = _loadShader(GL_FRAGMENT_SHADER, fragmentShaderSource);
    int shaderProgram = _createProgram(vertexShader, fragmentShader);
    _flutterOpenGL.glUseProgram(shaderProgram);

    // 获取属性位置
    int positionAttribLocation = _flutterOpenGL.glGetAttribLocation(shaderProgram, 'a_position');
    _flutterOpenGL.glEnableVertexAttribArray(positionAttribLocation);

    // 设置顶点数据
    Float32List vertices = Float32List.fromList([
      -0.5, -0.5,
      0.5, -0.5,
      0.0, 0.5,
    ]);
    Uint16List indices = Uint16List.fromList([0, 1, 2]);

    // 创建并绑定缓冲区
    int vertexBuffer = _flutterOpenGL.glGenBuffers();
    _flutterOpenGL.glBindBuffer(GL_ARRAY_BUFFER, vertexBuffer);
    _flutterOpenGL.glBufferData(GL_ARRAY_BUFFER, vertices, GL_STATIC_DRAW);

    int indexBuffer = _flutterOpenGL.glGenBuffers();
    _flutterOpenGL.glBindBuffer(GL_ELEMENT_ARRAY_BUFFER, indexBuffer);
    _flutterOpenGL.glBufferData(GL_ELEMENT_ARRAY_BUFFER, indices, GL_STATIC_DRAW);

    // 指定顶点属性指针
    _flutterOpenGL.glVertexAttribPointer(positionAttribLocation, 2, GL_FLOAT, false, 0, 0);
  }

  int _loadShader(int type, String source) {
    int shader = _flutterOpenGL.glCreateShader(type);
    _flutterOpenGL.glShaderSource(shader, source);
    _flutterOpenGL.glCompileShader(shader);

    int compileStatus = _flutterOpenGL.glGetShaderiv(shader, GL_COMPILE_STATUS);
    if (compileStatus == 0) {
      String infoLog = _flutterOpenGL.glGetShaderInfoLog(shader);
      throw Exception('Failed to compile shader: $infoLog');
    }
    return shader;
  }

  int _createProgram(int vertexShader, int fragmentShader) {
    int program = _flutterOpenGL.glCreateProgram();
    _flutterOpenGL.glAttachShader(program, vertexShader);
    _flutterOpenGL.glAttachShader(program, fragmentShader);
    _flutterOpenGL.glLinkProgram(program);

    int linkStatus = _flutterOpenGL.glGetProgramiv(program, GL_LINK_STATUS);
    if (linkStatus == 0) {
      String infoLog = _flutterOpenGL.glGetProgramInfoLog(program);
      throw Exception('Failed to link program: $infoLog');
    }
    return program;
  }

  void render() {
    _flutterOpenGL.glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);

    // 绘制三角形
    int indexCount = 3;
    _flutterOpenGL.glDrawElements(GL_TRIANGLES, indexCount, GL_UNSIGNED_SHORT, 0);

    // 交换缓冲区
    _flutterOpenGL.glFlush();
    _flutterOpenGL.glFinish();
    _window.scheduleFrame();
  }

  void dispose() {
    _flutterOpenGL.dispose();
  }
}

class _OpenGLPainter extends CustomPainter {
  final OpenGLRenderer renderer;

  _OpenGLPainter(this.renderer);

  @override
  void paint(Canvas canvas, Size size) {
    renderer.render();
  }

  @override
  bool shouldRepaint(covariant CustomPainter oldDelegate) {
    return false;
  }
}

const String vertexShaderSource = '''
attribute vec4 a_position;
void main() {
  gl_Position = a_position;
}
''';

const String fragmentShaderSource = '''
void main() {
  gl_FragColor = vec4(1.0, 0.0, 0.0, 1.0); // 红色
}
''';

在这个示例中，我们创建了一个自定义的OpenGLWidget，它包含一个OpenGLRenderer对象来管理OpenGL的渲染逻辑。OpenGLRenderer类负责初始化OpenGL状态、加载着色器、设置顶点数据，并在每一帧中渲染内容。

请注意，这个示例假设你已经正确设置了Flutter开发环境，并且flutter_opengl插件是可用的。如果flutter_opengl插件的API有所变化，你可能需要根据最新的文档进行调整。此外，由于OpenGL渲染的复杂性，这个示例仅展示了基本的渲染流程，实际应用中可能需要更多的错误处理和资源管理。