Types

All properties in Slint have a type. Slint knows these basic types:

Name	description	Default value
angle	Angle measurement, corresponds to a literal like 90deg, 1.2rad, 0 25turn	0deg
bool	boolean whose value can be either true or false.	false
duration	Type for the duration of animations. A suffix like ms (millisecond) or s (second) is used to indicate the precision.	0ms
easing	Property animation allow specifying an easing curve. See animations for list of values.	linear
float	Signed, 32-bit floating point number. Numbers with a % suffix are automatically divided by 100, so for example 30% is the same as 0.30.	0
image	A reference to an image, can be initialized with the @image-url("...") construct	empty image
int	Signed integral number.	0
length	The type used for x, y, width and height coordinates. Corresponds to a literal like 1px, 1pt, 1in, 1mm, or 1cm. It can be converted to and from length provided the binding is run in a context where there is an access to the device pixel ratio.	0px
percent	Signed, 32-bit floating point number that is interpreted as percentage. Literal number assigned to properties of this type must have a % suffix.	0%
physical-length	This is an amount of physical pixels. To convert from an integer to a length unit, one can simply multiply by 1px. Or to convert from a length to a float, one can divide by 1phx.	0phx
relative-font-size	Relative font size factor that is multiplied with the Window.default-font-size and can be converted to a length.	0rem
string	UTF-8 encoded, reference counted string.	""

Please see the language specific API references how these types are mapped to the APIs of the different programming languages.

Images

The image type is a reference to an image. It’s defined using the @image-url("...") construct. The address within the @image-url function must be known at compile time.

Slint looks for images in the following places:

1. The absolute path or the path relative to the current .slint file.
2. The include path used by the compiler to look up .slint files.

Access an image’s dimension using its width and height properties.

export component Example inherits Window {
    preferred-width: 150px;
    preferred-height: 50px;

    in property <image> some_image: @image-url("https://slint.dev/logo/slint-logo-full-light.svg");

    Text {
        text: "The image is " + some_image.width + "x" + some_image.height;
    }
}

It is also possible to load images supporting 9 slice scaling ↗ (also called nine patch or border images) by adding a nine-slice(...) argument. The argument can have either one, two, or four numbers that specifies the size of the edges. The numbers are either top right bottom left or vertical horizontal, or one number for everything

String

Any sequence of utf-8 encoded characters surrounded by quotes is a string: "foo".

Escape sequences may be embedded into strings to insert characters that would be hard to insert otherwise:

Escape	Result
\"	"
\\	\
\n	new line
\u{x}	where x is a hexadecimal number, expands to the unicode code point represented by this number
\{expression}	the result of evaluating the expression

Anything else following an unescaped \ is an error.

export component Example inherits Text {
    text: "hello";
}

Note

The \{...} syntax is not valid within the slint! macro in Rust.

Colors and Brushes

Color literals follow the syntax of CSS:

export component Example inherits Window {
    background: blue;
    property<color> c1: #ffaaff;
    property<brush> b2: Colors.red;
}

In addition to plain colors, many elements have properties that are of type brush instead of color. A brush is a type that can be either a color or gradient. The brush is then used to fill an element or draw the outline.

CSS Color names are only in scope in expressions of type color or brush. Otherwise, you can access colors from the Colors namespace.

Properties

The following properties are exposed:

• red
• green
• blue
• alpha

These properties are in the range 0-255.

Methods

All colors and brushes define the following methods:

• brighter(factor: float) -> brush

  Returns a new color derived from this color but has its brightness increased by the specified factor. This is done by converting the color to the HSV color space and multiplying the brightness (value) with (1 + factor). For example if the factor is 0.5 (or for example 50%) the returned color is 50% brighter. Negative factors decrease the brightness.

• darker(factor: float) -> brush

  Returns a new color derived from this color but has its brightness decreased by the specified factor. This is done by converting the color to the HSV color space and dividing the brightness (value) by (1 + factor). For example if the factor is .5 (or for example 50%) the returned color is 50% darker. Negative factors increase the brightness.

• mix(other: brush, factor: float) -> brush

  Returns a new color that is a mix of this color and other. The specified factor is clamped to be between 0.0 and 1.0 and then applied to this color, while 1.0 - factor is applied to other. For example red.mix(green, 70%) will have a stronger tone of red, while red.mix(green, 30%) will have a stronger tone of green.

• transparentize(factor: float) -> brush

  Returns a new color with the opacity decreased by factor. The transparency is obtained by multiplying the alpha channel by (1 - factor).

• with-alpha(alpha: float) -> brush

  Returns a new color with the alpha value set to alpha (between 0 and 1)

• to-hsv()->{hue: float, saturation: float, value: float, alpha: float} “ Converts this color to the HSV color space and returns a struct with the hue, saturation, value, and alpha fields. hue is between 0 and 360 while saturation, value, and alpha are between 0 and 1.

Linear Gradients

Linear gradients describe smooth, colorful surfaces. They’re specified using an angle and a series of color stops. The colors will be linearly interpolated between the stops, aligned to an imaginary line that is rotated by the specified angle. This is called a linear gradient and is specified using the @linear-gradient macro with the following signature:

@linear-gradient(angle, color percentage, color percentage, ...)

The first parameter to the macro is an angle (see Types). The gradient line’s starting point will be rotated by the specified value.

Following the initial angle is one or multiple color stops, describe as a space separated pair of a color value and a percentage. The color specifies which value the linear color interpolation should reach at the specified percentage along the axis of the gradient.

The following example shows a rectangle that’s filled with a linear gradient that starts with a light blue color, interpolates to a very light shade in the center and finishes with an orange tone:

export component Example inherits Window {
    preferred-width: 100px;
    preferred-height: 100px;

    Rectangle {
        background: @linear-gradient(90deg, #3f87a6 0%, #ebf8e1 50%, #f69d3c 100%);
    }
}

Radial Gradients

Radial gradients are like linear gradients but the colors are interpolated circularly instead of along a line. To describe a radial gradient, use the @radial-gradient macro with the following signature:

@radial-gradient(circle, color percentage, color percentage, ...)

The first parameter to the macro is always circle because only circular gradients are supported. The syntax is otherwise based on the CSS radial-gradient function.

Example:

export component Example inherits Window {
    preferred-width: 100px;
    preferred-height: 100px;
    Rectangle {
        background: @radial-gradient(circle, #f00 0%, #0f0 50%, #00f 100%);
    }
}

Structs

Define named structures using the struct keyword:

export struct Player  {
    name: string,
    score: int,
}

export component Example {
    in-out property<Player> player: { name: "Foo", score: 100 };
}

The default value of a struct, is initialized with all its fields set to their default value.

Anonymous Structures

Declare anonymous structures using { identifier1: type1, identifier2: type2 } syntax, and initialize them using { identifier1: expression1, identifier2: expression2 }.

You may have a trailing , after the last expression or type.

export component Example {
    in-out property<{name: string, score: int}> player: { name: "Foo", score: 100 };
    in-out property<{a: int, }> foo: { a: 3 };
}

Enums

Define an enumeration with the enum keyword:

export enum CardSuit { clubs, diamonds, hearts, spade }

export component Example {
    in-out property<CardSuit> card: spade;
    out property<bool> is-clubs: card == CardSuit.clubs;
}

Enum values can be referenced by using the name of the enum and the name of the value separated by a dot. (eg: CardSuit.spade)

The name of the enum can be omitted in bindings of the type of that enum, or if the return value of a callback is of that enum.

The default value of each enum type is always the first value.

Arrays and Models

Arrays are declared by wrapping [ and ] square brackets around the type of the array elements.

Array literals as well as properties holding arrays act as models in for expressions.

export component Example {
    in-out property<[int]> list-of-int: [1,2,3];
    in-out property<[{a: int, b: string}]> list-of-structs: [{ a: 1, b: "hello" }, {a: 2, b: "world"}];
}

Arrays define the following operations:

• array.length: One can query the length of an array and model using the builtin .length property.
• array[index]: The index operator retrieves individual elements of an array.

Out of bound access into an array will return default-constructed values.

export component Example {
    in-out property<[int]> list-of-int: [1,2,3];

    out property <int> list-len: list-of-int.length;
    out property <int> first-int: list-of-int[0];
}

Conversions

Slint supports conversions between different types. Explicit conversions are required to make the UI description more robust, but implicit conversions are allowed between some types for convenience.

The following conversions are possible:

• int can be converted implicitly to float and vice-versa. When converting from float to int, the value is truncated.
• int and float can be converted implicitly to string
• physical-length, relative-font-size, and length can be converted implicitly to each other only in context where the pixel ratio is known.
• the units type (length, physical-length, duration, …) can’t be converted to numbers (float or int) but they can be divided by themselves to result in a number. Similarly, a number can be multiplied by one of these unit. The idea is that one would multiply by 1px or divide by 1px to do such conversions
• The literal 0 can be converted to any of these types that have associated unit.
• Struct types convert with another struct type if they have the same property names and their types can be converted. The source struct can have either missing properties, or extra properties. But not both.
• Arrays generally don’t convert between each other. Array literals can be converted if the element types are convertible.
• String can be converted to float by using the to-float function. That function returns 0 if the string isn’t a valid number. You can check with is-float() if the string contains a valid number

export component Example {
    // OK: int converts to string
    property<{a: string, b: int}> prop1: {a: 12, b: 12 };
    // OK: even if a is missing, it will just have the default value ("")
    property<{a: string, b: int}> prop2: { b: 12 };
    // OK: even if c is too many, it will be discarded
    property<{a: string, b: int}> prop3: { a: "x", b: 12, c: 42 };
    // ERROR: b is missing and c is extra, this doesn't compile, because it could be a typo.
    // property<{a: string, b: int}> prop4: { a: "x", c: 42 };

    property<string> xxx: "42.1";
    property<float> xxx1: xxx.to-float(); // 42.1
    property<bool> xxx2: xxx.is-float(); // true
    property<int> xxx3: 45.8; // 45
}