提高开始速度并在结束时减速

Question

我有一个简单的功能，可以在特定的方向上移动一个圆圈：

var rad = (a) => Math.PI / 180 * a;

this.x += Math.cos(rad) * this.throttle();
this.y += Math.sin(rad) * this.throttle();

我也在计算与目标的距离：

var distance = (p1, p2) => Math.sqrt( (p1.x - p2.x) * (p1.x - p2.x) + (p1.y - p2.y) * (p1.y - p2.y) );

this.destination_distance = parseInt(distance( { x: this.x, y: this.y }, { x: x, y: y } ));

我开始研究this.throttle功能，但我无法理解它。

我想要实现简单的事情，当圈子开始移动时我希望通过某个步骤将速度从min提高到max，当它接近目的地时，我希望它开始减速直到它到达min。

这是我目前的做法：

this.min_speed = 0.1;
this.max_speed = 1.5;
this.current_speed = 0.1;

this.throttle = function() {
    if(this.destination_distance > 300) {
        this.current_speed += 0.002;
    } else {
        this.current_speed -= 0.002;
    }

    if(this.current_speed < this.min_speed) {
        this.current_speed = this.min_speed;
    }

    if(this.current_speed > this.max_speed) {
        this.current_speed = this.max_speed;
    }

    return this.current_speed;
};

这不起作用，因为如果距离小于300它总是以min速度加速，所以我想它应该以某种方式与distance相关联变量。也许有人可以帮我解决这个问题。

Answer 1

您需要计算目标速度和当前速度之间的差异，然后添加一些特定部分。

this.throttle = function() {
  var target_speed = this.destination_distance > 300 ? this.max_speed : this.min_speed;
  var diff = target_speed - this.current_speed;
  this.current_speed += diff * laziness;
  return this.current_speed;
};

laziness介于0.0001和1之间;值越大，速度变化越快。

Answer 2

您的起始速度是您的最低速度，因此如果起始距离<300，则圆圈将永远不会加速或减速。为什么不让你的起跑速度取决于初始距离？这是一个粗略的实现

private void uploadFile(String selectedFilePath) {

    final ProgressDialog pd = new ProgressDialog(MainActivity.this);
    pd.setMessage("loading");
    pd.show();

    Log.d("enter", "Entering" + selectedFilePath);

    if (selectedFilePath.equals("null")) {
        selectedFilePath = "";
    }

    int serverResponseCode = 0;

    HttpURLConnection connection;
    DataOutputStream dataOutputStream;
    String lineEnd = "\r\n";
    String twoHyphens = "--";
    String boundary = "*****";


    int bytesRead, bytesAvailable, bufferSize;
    byte[] buffer;
    int maxBufferSize = 1 * 1024 * 1024;
    File selectedFile = new File(selectedFilePath);

    String[] parts = selectedFilePath.split("/");
    final String fileName = parts[parts.length - 1];

    if (!selectedFile.isFile()) {
        // dialog.dismiss();

        MainActivity.this.runOnUiThread(new Runnable() {
            @Override
            public void run() {
                //tvFileName.setText("Source File Doesn't Exist: " + selectedFilePath);
            }
        });

    } else {
        try {
            FileInputStream fileInputStream = new FileInputStream(selectedFile);
            URL url = new URL(SERVER_URL);
            connection = (HttpURLConnection) url.openConnection();
            connection.setDoInput(true);//Allow Inputs
            connection.setDoOutput(true);//Allow Outputs
            connection.setUseCaches(false);//Don't use a cached Copy
            connection.setRequestMethod("POST");
            connection.setRequestProperty("Connection", "Keep-Alive");
            connection.setRequestProperty("ENCTYPE", "multipart/form-data");
            connection.setRequestProperty("Content-Type", "multipart/form-data;boundary=" + boundary);
            connection.setRequestProperty("image", fileName);
            connection.setRequestProperty("proof_file", fileName);

            //creating new dataoutputstream
            dataOutputStream = new DataOutputStream(connection.getOutputStream());

            String aID = "10";
            Log.e("Sending", "Sending userID");
            dataOutputStream.writeBytes(twoHyphens + boundary + lineEnd);
            dataOutputStream.writeBytes("Content-Disposition: form-data; name=\"a_id\"" + lineEnd);
            dataOutputStream.writeBytes(lineEnd);

            // assign value
            dataOutputStream.writeBytes(aID);
            dataOutputStream.writeBytes(lineEnd);
            dataOutputStream.writeBytes(twoHyphens + boundary + lineEnd);


            String saID = "1";
            Log.e("Sending", "Sending SocietyID");
            dataOutputStream.writeBytes(twoHyphens + boundary + lineEnd);
            dataOutputStream.writeBytes("Content-Disposition: form-data; name=\"s_id\"" + lineEnd);
            dataOutputStream.writeBytes(lineEnd);

            // assign value
            dataOutputStream.writeBytes(saID);
            dataOutputStream.writeBytes(lineEnd);
            dataOutputStream.writeBytes(twoHyphens + boundary + lineEnd);

            dataOutputStream.writeBytes(twoHyphens + boundary + lineEnd);
            dataOutputStream.writeBytes("Content-Disposition: form-data; name=\"name\"" + lineEnd);
            dataOutputStream.writeBytes(lineEnd);

            // assign value
            dataOutputStream.writeBytes(name);
            dataOutputStream.writeBytes(lineEnd);
            dataOutputStream.writeBytes(twoHyphens + boundary + lineEnd);

            dataOutputStream.writeBytes(twoHyphens + boundary + lineEnd);
            dataOutputStream.writeBytes("Content-Disposition: form-data; name=\"mobile\"" + lineEnd);
            dataOutputStream.writeBytes(lineEnd);

            // assign value
            dataOutputStream.writeBytes("38398393");
            dataOutputStream.writeBytes(lineEnd);
            dataOutputStream.writeBytes(twoHyphens + boundary + lineEnd);



            dataOutputStream.writeBytes(twoHyphens + boundary + lineEnd);
            dataOutputStream.writeBytes("Content-Disposition: form-data; name=\"address\"" + lineEnd);
            dataOutputStream.writeBytes(lineEnd);

            // assign value
            dataOutputStream.writeBytes("abc");
            dataOutputStream.writeBytes(lineEnd);
            dataOutputStream.writeBytes(twoHyphens + boundary + lineEnd);


            dataOutputStream.writeBytes(twoHyphens + boundary + lineEnd);
            dataOutputStream.writeBytes("Content-Disposition: form-data; name=\"h_type\"" + lineEnd);
            dataOutputStream.writeBytes(lineEnd);

            // assign value
            dataOutputStream.writeBytes("ty");
            dataOutputStream.writeBytes(lineEnd);
            dataOutputStream.writeBytes(twoHyphens + boundary + lineEnd);
            //..............................
            dataOutputStream.writeBytes(twoHyphens + boundary + lineEnd);
            dataOutputStream.writeBytes("Content-Disposition: form-data; name=\"proof_file\";filename=\""
                    + fileName + "\"" + lineEnd);

            dataOutputStream.writeBytes(lineEnd);

            dataOutputStream.writeBytes(twoHyphens + boundary + lineEnd);
            dataOutputStream.writeBytes("Content-Disposition: form-data; name=\"image\";filename=\""
                    + fileName + "\"" + lineEnd);



            dataOutputStream.writeBytes(lineEnd);


            dataOutputStream.writeBytes(String.valueOf(destination));
            dataOutputStream.writeBytes(lineEnd);
            dataOutputStream.writeBytes(twoHyphens + boundary + lineEnd);
            //...................9/6..................
            //returns no. of bytes present in fileInputStream
            bytesAvailable = fileInputStream.available();
            //selecting the buffer size as minimum of available bytes or 1 MB
            bufferSize = Math.min(bytesAvailable, maxBufferSize);
            //setting the buffer as byte array of size of bufferSize
            buffer = new byte[bufferSize];

            //reads bytes from FileInputStream(from 0th index of buffer to buffersize)
            bytesRead = fileInputStream.read(buffer, 0, bufferSize);

            //loop repeats till bytesRead = -1, i.e., no bytes are left to read
            while (bytesRead > 0) {
                //write the bytes read from inputstream
                dataOutputStream.write(buffer, 0, bufferSize);
                bytesAvailable = fileInputStream.available();
                bufferSize = Math.min(bytesAvailable, maxBufferSize);
                bytesRead = fileInputStream.read(buffer, 0, bufferSize);
            }

            dataOutputStream.writeBytes(lineEnd);
            dataOutputStream.writeBytes(twoHyphens + boundary + twoHyphens + lineEnd);

            serverResponseCode = connection.getResponseCode();
            String serverResponseMessage = connection.getResponseMessage();

            // Log.i(TAG, "Server Response is: " + serverResponseMessage + ": " + serverResponseCode);
            Log.d("wer", serverResponseMessage);

            //response code of 200 indicates the server status OK
            if (serverResponseCode == 200) {
              MainActivity.this.runOnUiThread(new Runnable() {
                    @Override
                    public void run() {
                        // tvFileName.setText("File Upload completed.\n\n You can see the uploaded file here: \n\n" + "http://coderefer.com/extras/uploads/"+ fileName);
                        Toast.makeText(MainActivity.this,"Successfully uploaded to server",Toast.LENGTH_SHORT).show();
                        pd.dismiss();
                    }
                });
            }
            else {

                Toast.makeText(MainActivity.this,"Something went wrong",Toast.LENGTH_SHORT).show();
                pd.dismiss();
            }
            //closing the input and output streams
            fileInputStream.close();
            dataOutputStream.flush();
            dataOutputStream.close();
        } catch (FileNotFoundException e) {
            e.printStackTrace();
           MainActivity.this.runOnUiThread(new Runnable() {
                @Override
                public void run() {
                    Toast.makeText(MainActivity.this, "File Not Found", Toast.LENGTH_SHORT).show();
                }
            });
        } catch (MalformedURLException e) {
            e.printStackTrace();
            Toast.makeText(MainActivity.this, "URL error!", Toast.LENGTH_SHORT).show();

        } catch (IOException e) {
            e.printStackTrace();
            Toast.makeText(MainActivity.this, "Cannot Read/Write File!", Toast.LENGTH_SHORT).show();
        }
        pd.dismiss();
    }
}

Answer 3

为什么不使用总距离的百分比？这样你就可以避免使用300的硬编码阈值，它应该适用于任意长度的距离（通过调整一些速度）。你改变的功能看起来像这样：

this.throttle = function() {
    if(this.destination_distance > 0.5 * total_distance) {
        this.current_speed += 0.002;
    } else {
        this.current_speed -= 0.002;
    }

    if(this.current_speed < this.min_speed) {
        this.current_speed = this.min_speed;
    }

    if(this.current_speed > this.max_speed) {
        this.current_speed = this.max_speed;
    }

    return this.current_speed;
};

这里我认为total_distance是从开始到最终目的地的距离。这样，圆圈将以增加的速度行进大约一半，而另一半以减小的速度行进。如果用let 0.8替换0.5，那么前80％的速度会增加，而路径的最后20％的速度会减少。