flutter_lua_runtime/lib/runtime/display/runtime_viewport.dart

import 'package:flame/components.dart';

class RuntimeScaleMode {
  const RuntimeScaleMode._();

  static const fit = 'fit';
  static const fill = 'fill';
  static const stretch = 'stretch';
  static const none = 'none';

  static const all = {fit, fill, stretch, none};

  static bool isSupported(String value) => all.contains(value);
}

class RuntimeViewportConfig {
  const RuntimeViewportConfig({
    required this.designWidth,
    required this.designHeight,
    this.scaleMode = RuntimeScaleMode.fit,
  });

  final double designWidth;
  final double designHeight;
  final String scaleMode;

  Vector2 get designSize => Vector2(designWidth, designHeight);
}

class RuntimeViewportTransform {
  const RuntimeViewportTransform({
    required this.x,
    required this.y,
    required this.width,
    required this.height,
    required this.scaleX,
    required this.scaleY,
    required this.scaleMode,
  });

  final double x;
  final double y;
  final double width;
  final double height;
  final double scaleX;
  final double scaleY;
  final String scaleMode;

  Map<String, Object?> toMap() {
    return {
      'x': x,
      'y': y,
      'width': width,
      'height': height,
      'scaleX': scaleX,
      'scaleY': scaleY,
      'scaleMode': scaleMode,
    };
  }
}

class RuntimeViewport {
  const RuntimeViewport._();

  static RuntimeViewportTransform compute({
    required Vector2 screenSize,
    required RuntimeViewportConfig config,
  }) {
    final designWidth = config.designWidth;
    final designHeight = config.designHeight;
    final screenWidth = screenSize.x;
    final screenHeight = screenSize.y;

    if (designWidth <= 0 || designHeight <= 0) {
      throw const FormatException('Runtime viewport design size must be > 0');
    }
    if (!RuntimeScaleMode.isSupported(config.scaleMode)) {
      throw FormatException(
        'Runtime viewport scaleMode is unsupported: ${config.scaleMode}',
      );
    }

    final safeScreenWidth = screenWidth <= 0 ? designWidth : screenWidth;
    final safeScreenHeight = screenHeight <= 0 ? designHeight : screenHeight;

    final scaleX = safeScreenWidth / designWidth;
    final scaleY = safeScreenHeight / designHeight;

    return switch (config.scaleMode) {
      RuntimeScaleMode.fit => _uniform(
        designWidth: designWidth,
        designHeight: designHeight,
        screenWidth: safeScreenWidth,
        screenHeight: safeScreenHeight,
        scale: scaleX < scaleY ? scaleX : scaleY,
        scaleMode: config.scaleMode,
      ),
      RuntimeScaleMode.fill => _uniform(
        designWidth: designWidth,
        designHeight: designHeight,
        screenWidth: safeScreenWidth,
        screenHeight: safeScreenHeight,
        scale: scaleX > scaleY ? scaleX : scaleY,
        scaleMode: config.scaleMode,
      ),
      RuntimeScaleMode.stretch => RuntimeViewportTransform(
        x: 0,
        y: 0,
        width: safeScreenWidth,
        height: safeScreenHeight,
        scaleX: scaleX,
        scaleY: scaleY,
        scaleMode: config.scaleMode,
      ),
      RuntimeScaleMode.none => RuntimeViewportTransform(
        x: (safeScreenWidth - designWidth) / 2,
        y: (safeScreenHeight - designHeight) / 2,
        width: designWidth,
        height: designHeight,
        scaleX: 1,
        scaleY: 1,
        scaleMode: config.scaleMode,
      ),
      _ => throw FormatException(
        'Runtime viewport scaleMode is unsupported: ${config.scaleMode}',
      ),
    };
  }

  static void apply(
    PositionComponent root,
    RuntimeViewportTransform transform,
  ) {
    root
      ..position = Vector2(transform.x, transform.y)
      ..scale = Vector2(transform.scaleX, transform.scaleY)
      ..size = Vector2(transform.width, transform.height);
  }

  static RuntimeViewportTransform _uniform({
    required double designWidth,
    required double designHeight,
    required double screenWidth,
    required double screenHeight,
    required double scale,
    required String scaleMode,
  }) {
    final width = designWidth * scale;
    final height = designHeight * scale;
    return RuntimeViewportTransform(
      x: (screenWidth - width) / 2,
      y: (screenHeight - height) / 2,
      width: width,
      height: height,
      scaleX: scale,
      scaleY: scale,
      scaleMode: scaleMode,
    );
  }
}