Android游戏开发：基于线段交点的精确碰撞检测

import android.graphics.PointF; // PointF 适用于浮点数坐标

public class Vector2D extends PointF {
    public Vector2D(float x, float y) {
        super(x, y);
    }
}

public class LineSegment {
    public Vector2D p1;
    public Vector2D p2;

    public LineSegment(Vector2D p1, Vector2D p2) {
        this.p1 = p1;
        this.p2 = p2;
    }

    public LineSegment(float x1, float y1, float x2, float y2) {
        this.p1 = new Vector2D(x1, y1);
        this.p2 = new Vector2D(x2, y2);
    }
}

public class IntersectionUtils {

    /**
     * 计算两条线段的交点。
     * 如果存在交点且交点在线段范围内，则返回交点坐标；否则返回null。
     *
     * @param seg1 第一条线段
     * @param seg2 第二条线段
     * @return 交点坐标 (PointF) 或 null
     */
    public static PointF getIntersectionPoint(LineSegment seg1, LineSegment seg2) {
        float x1 = seg1.p1.x, y1 = seg1.p1.y;
        float x2 = seg1.p2.x, y2 = seg1.p2.y;
        float x3 = seg2.p1.x, y3 = seg2.p1.y;
        float x4 = seg2.p2.x, y4 = seg2.p2.y;

        // 计算 A, B, C 参数 for seg1
        float A1 = y1 - y2;
        float B1 = x2 - x1;
        float C1 = x1 * y2 - x2 * y1;

        // 计算 A, B, C 参数 for seg2
        float A2 = y3 - y4;
        float B2 = x4 - x3;
        float C2 = x3 * y4 - x4 * y3;

        // 计算分母
        float denominator = A1 * B2 - A2 * B1;

        // 如果分母接近0，则线段平行或重合
        if (Math.abs(denominator) < 0.0001f) { // 使用一个小的 epsilon 值来处理浮点数精度
            return null; // 平行或重合，不认为有有效交点
        }

        // 计算交点坐标
        float intersectX = (C2 * B1 - C1 * B2) / denominator;
        float intersectY = (C1 * A2 - C2 * A1) / denominator;

        // 检查交点是否落在第一条线段的范围内
        if (!isPointOnSegment(intersectX, intersectY, seg1)) {
            return null;
        }

        // 检查交点是否落在第二条线段的范围内
        if (!isPointOnSegment(intersectX, intersectY, seg2)) {
            return null;
        }

        return new PointF(intersectX, intersectY);
    }

    /**
     * 检查一个点是否在线段的包围盒内（即是否在线段上）。
     *
     * @param x 点的X坐标
     * @param y 点的Y坐标
     * @param seg 线段
     * @return 如果点在线段上则返回true，否则返回false
     */
    private static boolean isPointOnSegment(float x, float y, LineSegment seg) {
        float minX = Math.min(seg.p1.x, seg.p2.x);
        float maxX = Math.max(seg.p1.x, seg.p2.x);
        float minY = Math.min(seg.p1.y, seg.p2.y);
        float maxY = Math.max(seg.p1.y, seg.p2.y);

        // 允许一个小范围的浮点误差
        final float EPSILON = 0.0001f;

        return x >= minX - EPSILON && x <= maxX + EPSILON &&
               y >= minY - EPSILON && y <= maxY + EPSILON;
    }
}

// ... PongView 类的其他成员变量和方法 ...

protected void collisionCheck() {
    // 处理屏幕边界碰撞 (保持原有逻辑)
    // ...

    // 创建球的运动轨迹线段
    LineSegment ballTrajectory = new LineSegment(oldBallX, oldBallY, ballX, ballY);

    // 获取右侧挡板的碰撞边缘线段
    float rPaddleX = 7 * screenWidth / 8;
    float rPaddleTopY = rPaddle * screenHeight - halfPaddle;
    float rPaddleBottomY = rPaddle * screenHeight + halfPaddle;
    LineSegment rightPaddleCollisionEdge = new LineSegment(rPaddleX, rPaddleTopY, rPaddleX, rPaddleBottomY);

    // 获取左侧挡板的碰撞边缘线段
    float lPaddleX = screenWidth / 8 + 15; // 左挡板的右边缘
    float lPaddleTopY = lPaddle * screenHeight - halfPaddle;
    float lPaddleBottomY = lPaddle * screenHeight + halfPaddle;
    LineSegment leftPaddleCollisionEdge = new LineSegment(lPaddleX, lPaddleTopY, lPaddleX, lPaddleBottomY);

    // 检测与右侧挡板的碰撞
    PointF intersectionWithRightPaddle = IntersectionUtils.getIntersectionPoint(ballTrajectory, rightPaddleCollisionEdge);
    if (intersectionWithRightPaddle != null) {
        // 发生碰撞，调整球的速度方向
        ballSpeedX *= -1.0f;
        // 可选：将球的位置调整到交点处，以避免穿透
        // ballX = intersectionWithRightPaddle.x;
        // ballY = intersectionWithRightPaddle.y;
        // 如果调整了位置，需要重新计算剩余时间内的运动
        // 播放碰撞音效
        MediaPlayer pip = MediaPlayer.create(_context.getApplicationContext(), R.raw.lil_pip);
        pip.start();
        pip.setOnCompletionListener(MediaPlayer::release); // 释放资源
    }

    // 检测与左侧挡板的碰撞
    PointF intersectionWithLeftPaddle = IntersectionUtils.getIntersectionPoint(ballTrajectory, leftPaddleCollisionEdge);
    if (intersectionWithLeftPaddle != null) {
        // 发生碰撞，调整球的速度方向
        ballSpeedX *= -1.0f;
        // 可选：将球的位置调整到交点处
        // ballX = intersectionWithLeftPaddle.x;
        // ballY = intersectionWithLeftPaddle.y;
        // 播放碰撞音效
        MediaPlayer pip = MediaPlayer.create(_context.getApplicationContext(), R.raw.lil_pip);
        pip.start();
        pip.setOnCompletionListener(MediaPlayer::release); // 释放资源
    }

    Log.d("TAG", "Ball is moving");
}