文档

Unity Engine

User Manual

Script Reference

Unity Engine

USS data types

USS data types define typical values accepted by USS properties and functions.
阅读时间5 分钟最后更新于 1 个月前
USS data types define typical values, including keywords and units, that USS properties and functions accept.

Syntax

USS properties use the same syntax as W3C CSS documents:
  • Keyword values appear as is. For example: 
    auto
    , 
    baseline
    .
  • Basic data types appear between angle brackets ( 
    <
    and 
    >
    ). For example: 
    <length>
    and 
    <color>
    .
  • Non-terminals that share the same name as a property appear between angle brackets and single straight quotes ( 
    <'
    and 
    '>
    ). For example, 
    <'width'>
    .
If a property value has more than one option, the following applies:
  • Side-by-side words mean that all options must occur in the given order.
  • A bar (
    |
    ) separates two or more options. One of them must occur.
  • Double bars (
    ||
    ) separate two or more options. One or more of them must occur in any order.
  • Double ampersands (
    &&
    ) separate two or more options. All options must occur.
  • Square brackets (
    [
    ]
    ) denote grouping.
Every type, keyword, or angle-bracketed group might be followed by modifiers. The following table lists the possible modifiers:

Modifier

The preceding type, keyword, or group

An asterisk (
*
)		Occurs zero or more times
A plus sign (
+
)		Occurs one or more times
A question mark (
?
)		Is optional
A pair of numbers in curly braces (
{A,B}
)		Occurs at least 
A
and at most 
B
times

Length

UI Toolkit supports pixels(
px
) and percentages (
%
) as units of measurement for length. Pixel values are absolute, while percentages are relative to the element's parent.
Examples:
  • width:200px;
    expresses a width of 200 px.
  • width:50%;
    expresses a width of half of the parent element's width.
It's important to specify the unit of measurement. If you don't specify a unit of measurement, UI Toolkit assumes that the property value is expressed in px.
注意
0
is a special value that doesn't require a unit of measurement.

Numeric

Numeric values are expressed as either floating points or integer literals. For example, 
flex:1.0
.

Keywords

Specific keywords are supported for some built-in properties. Keywords give a descriptive name instead of a number. For example: 
position:absolute
.
All properties support the 
initial
global keyword which resets the default value of a property to an element.
In the following example, although you set the color of all the labels to red, the 
initial
keyword of 
color
restores the color of 
label1
to its default value:
/* Set the color of all the labels to red. */Label {    color: red;}/* label1 is the name of a specific label. */#label1{    color: initial;}

Color

UI Toolkit supports the following literal color values and functions:
  • A Hexadecimal value: 
    #FFFF00
    , 
    #0F0
  • The RGB function: 
    rgb(255, 255, 0)
  • The RGBA function: 
    rgba(255, 255, 0, 1.0)
  • Color keywords

Assets

You can reference project assets such as fonts and textures from your USS files. For example, you might reference a texture to use as the background image for an element.
To reference an asset, you can use either the 
url()
function or the 
resource()
function:
  • resource()
    : Represents an asset in a 
    Resources
    folder.
  • url()
    : Represents an asset specified by a path. You can express it as either a relative path or an absolute path.
Use the 
url()
function in most cases. However, the 
resource()
function supports automatically loading different versions of image assets for different screen densities.

Reference assets with the URL function

When you reference an asset with the 
url()
function, the path you specify can be relative or absolute:
  • Relative paths must be relative to the folder that contains the USS file that references the asset.
  • Absolute paths are relative to the project.
The path must include the file extension.
For example, if your project has a 
USS
folder that contains all your style sheets, and a 
Resources
folder that contains all your image assets.
Assets  └─ Editor      └─ Resources      └─ USS
To reference an image named 
thumb.png
, you can use one of the following paths:

Relative path

Absolute path

url("../Resources/thumb.png")
url("/Assets/Editor/Resources/thumb.png")


url("project:/Assets/Editor/Resources/thumb.png")


url("project:///Assets/Editor/Resources/thumb.png")
To reference an image in a package, use the 
Packages
folder in the path:

Relative path

Absolute path

url("../Packages/com.my.example.package/Editor/Resources/thumb.png")
url("Project:///Packages/com.my.example.package/Editor/Resources/thumb.png")

Reference assets with the resource function

The 
resource()
function can reference assets in Unity's resource folders (
Resources
and 
Editor Default Resources
). You reference an asset by name.
  • If the file is in the 
    Editor Default Resources
    folder, you must include the file extension.
  • If the file is in the 
    Resources
    folder, you must not include the file extension.
For example:

Path to file

Reference syntax

Assets/Resources/Images/my-image.png
resource("Images/my-image")
Assets/Editor Default Resources/Images/my-image.png
resource("Images/default-image.png")

Reference image assets for High DPI/Retina screens

To support screens with different screen densities (DPI), do the following:
  • Make sure that the high DPI versions of your textures have a 
    @2x
    suffix in their file names. For example the high DPI version of 
    myimage.png
    should be 
    myimage@2x.png
  • Place the regular and high DPI versions of the texture assets in the same project folder.
When Unity loads the asset, it automatically chooses the correct version for the current screen DPI.
For example, if you use 
resource("myimage")
in USS, Unity loads either 
Resources/myimage.png
or 
Resources/myimage@2x.png
.

Strings

Use quotes to specify a string value. For example: 
--my-property: "foo"
.

Additional resources