C#中for循环内height值未随index更新问题求助

我需要在每个循环周期中通过公式计算新的height整数值，但尽管index变量在循环中不断递增，height始终等于180。相关代码及控制台输出如下：

internal class Program
{
    static void Main(string[] args)
    {
        ///some code
        WorkContainer.StartUp(Source, Mode, Output);
    }
}

internal class WorkContainer
{
    public static void StartUp(string Source, string Mode, string Output)
    {   
        ///some code
        int maxWidth = 180;
        int maxHeight = 420;
        int framerate = 30;

        switch (Mode)
        {
            case "Bouncing":
                int delta = 5;
                double bouncesPerSecond = 1.5;
                int index = 0;
                int height = (int)(index == 0 ? maxHeight : (Math.Floor(Math.Abs(Math.Cos(index / (framerate / bouncesPerSecond) * Math.PI) * (maxHeight - delta))) + delta));
                ffmpegWork.ffmpegPngChangeResolution(CurrentDirectory, RandomTempFolderIdentity, index, maxWidth, height);
                break;
        }
    }
}

internal class ffmpegWork 
{
    public static void ffmpegPngChangeResolution(string CurrentDirectory, string RandomTempFolderIdentity, int index, int maxWidth, int height)
    {
        int ImgValues = new DirectoryInfo($"{CurrentDirectory}/Temp{RandomTempFolderIdentity}/img/").GetFiles().Length;
        for (int i = 0; i < ImgValues; i++, index++)
        {
            try
            { 
                Process compiler = new Process();
                        compiler.StartInfo.FileName = $"{CurrentDirectory}/ffmpeg/bin/ffmpeg";
                        compiler.StartInfo.Arguments = $"-y -i {CurrentDirectory}/Temp{RandomTempFolderIdentity}/img/img-{i + 1}.png -vf scale={maxWidth}:{height} -c:a libvorbis {CurrentDirectory}/Temp{RandomTempFolderIdentity}/webmImg/img-{i + 1}.png";
                        compiler.StartInfo.RedirectStandardOutput = true;
                        compiler.StartInfo.CreateNoWindow = true;
                        compiler.StartInfo.UseShellExecute = false;
                        compiler.Start();
                Console.WriteLine($"png frame - {i + 1}/{ImgValues}\nheight={height}");
            }
            catch (Exception e)
            {
                Console.WriteLine(e.Message);
            }
        }
    }
}

控制台输出 #

png frame - 1/n
height=180
png frame - 2/n
height=180
png frame - 3/n
height=180

问题原因 #

• height值仅初始化一次：在WorkContainer.StartUp方法中，height只在调用ffmpegPngChangeResolution前计算了一次，之后传入方法的是固定值，循环内部没有重新计算。
• 整数除法潜在风险：虽然当前代码中framerate / bouncesPerSecond会得到浮点值，但如果后续参数类型调整，index（整数）参与除法可能导致精度丢失，影响余弦函数的计算结果。

修复方案 #

将height的计算逻辑移到循环内部，同时把计算所需的参数传入方法，确保每次循环都能根据当前index重新计算：

1. 修改WorkContainer.StartUp中的调用逻辑 #

case "Bouncing":
    int delta = 5;
    double bouncesPerSecond = 1.5;
    int index = 0;
    // 不再提前计算height，传入计算所需的所有参数
    ffmpegWork.ffmpegPngChangeResolution(CurrentDirectory, RandomTempFolderIdentity, index, maxWidth, maxHeight, delta, framerate, bouncesPerSecond);
    break;

2. 修改ffmpegPngChangeResolution方法 #

internal class ffmpegWork 
{
    public static void ffmpegPngChangeResolution(string CurrentDirectory, string RandomTempFolderIdentity, int index, int maxWidth, int maxHeight, int delta, int framerate, double bouncesPerSecond)
    {
        int ImgValues = new DirectoryInfo($"{CurrentDirectory}/Temp{RandomTempFolderIdentity}/img/").GetFiles().Length;
        for (int i = 0; i < ImgValues; i++, index++)
        {
            try
            { 
                // 每次循环重新计算height
                int height = (int)(index == 0 
                    ? maxHeight 
                    : (Math.Floor(Math.Abs(Math.Cos((double)index / (framerate / bouncesPerSecond) * Math.PI) * (maxHeight - delta))) + delta));
                
                Process compiler = new Process();
                compiler.StartInfo.FileName = $"{CurrentDirectory}/ffmpeg/bin/ffmpeg";
                compiler.StartInfo.Arguments = $"-y -i {CurrentDirectory}/Temp{RandomTempFolderIdentity}/img/img-{i + 1}.png -vf scale={maxWidth}:{height} -c:a libvorbis {CurrentDirectory}/Temp{RandomTempFolderIdentity}/webmImg/img-{i + 1}.png";
                compiler.StartInfo.RedirectStandardOutput = true;
                compiler.StartInfo.CreateNoWindow = true;
                compiler.StartInfo.UseShellExecute = false;
                compiler.Start();
                
                Console.WriteLine($"png frame - {i + 1}/{ImgValues}\nheight={height}");
            }
            catch (Exception e)
            {
                Console.WriteLine(e.Message);
            }
        }
    }
}

关键调整说明 #

• 将height计算逻辑移入循环，确保每次循环都能基于最新的index值重新计算。
• 显式将index转换为double，避免整数除法可能导致的精度丢失问题，保证余弦函数计算的准确性。
• 传递计算height所需的全部参数，确保方法内的计算逻辑独立完整。

内容的提问来源于stack exchange，提问作者Dokoa