Time.deltaTime

描述

The interval in seconds from the last frame to the current one (Read Only).

When this is called from inside MonoBehaviour.FixedUpdate, it returns Time.fixedDeltaTime.

deltaTime inside MonoBehaviour.OnGUI is not reliable, because Unity might call it multiple times per frame.

The following example rotates a GameObject around its z axis at a constant speed.

using UnityEngine;
// Rotate around the z axis at a constant speed
public class ConstantRotation : MonoBehaviour
{
    public float degreesPerSecond = 2.0f;
    void Update()
    {
        transform.Rotate(0, 0, degreesPerSecond * Time.deltaTime);
    }
}

The following example implements a timer. The timer adds deltaTime each frame. The example displays the timer value and resets it when it reaches 2 seconds. Time.timeScale controls the speed at which time passes and how fast the timer resets.

using System.Collections;
using System.Collections.Generic;
using UnityEngine;

// Time.deltaTime example.
//
// Wait two seconds and display waited time.
// This is typically just beyond 2 seconds.
// Allow the speed of the time to be increased or decreased.
// It can range between 0.5 and 2.0. These changes only
// happen when the timer restarts.

public class ScriptExample : MonoBehaviour
{
    private float waitTime = 2.0f;
    private float timer = 0.0f;
    private float visualTime = 0.0f;
    private int width, height;
    private float value = 10.0f;
    private float scrollBar = 1.0f;

    void Awake()
    {
        width = Screen.width;
        height = Screen.height;
        Time.timeScale = scrollBar;
    }

    void Update()
    {
        timer += Time.deltaTime;

        // Check if we have reached beyond 2 seconds.
        // Subtracting two is more accurate over time than resetting to zero.
        if (timer > waitTime)
        {
            visualTime = timer;

            // Remove the recorded 2 seconds.
            timer = timer - waitTime;
            Time.timeScale = scrollBar;
        }
    }

    void OnGUI()
    {
        GUIStyle sliderDetails = new GUIStyle(GUI.skin.GetStyle("horizontalSlider"));
        GUIStyle sliderThumbDetails = new GUIStyle(GUI.skin.GetStyle("horizontalSliderThumb"));
        GUIStyle labelDetails = new GUIStyle(GUI.skin.GetStyle("label"));

        // Set the size of the fonts and the width/height of the slider.
        labelDetails.fontSize = 6 * (width / 200);
        sliderDetails.fixedHeight = height / 32;
        sliderDetails.fontSize = 12 * (width / 200);
        sliderThumbDetails.fixedHeight = height / 32;
        sliderThumbDetails.fixedWidth = width / 32;

        // Show the slider. Make the scale to be ten times bigger than the needed size.
        value = GUI.HorizontalSlider(new Rect(width / 8, height / 4, width - (4 * width / 8), height - (2 * height / 4)),
            value, 5.0f, 20.0f, sliderDetails, sliderThumbDetails);

        // Show the value from the slider. Make sure that 0.5, 0.6... 1.9, 2.0 are shown.
        float v = ((float)Mathf.RoundToInt(value)) / 10.0f;
        GUI.Label(new Rect(width / 8, height / 3.25f, width - (2 * width / 8), height - (2 * height / 4)),
            "timeScale: " + v.ToString("f1"), labelDetails);
        scrollBar = v;

        // Display the recorded time in a certain size.
        labelDetails.fontSize = 14 * (width / 200);
        GUI.Label(new Rect(width / 8, height / 2, width - (2 * width / 8), height - (2 * height / 4)),
            "Timer value is: " + visualTime.ToString("f4") + " seconds.", labelDetails);
    }
}