#### The Node file format [src]

GSK render nodes can be serialized and deserialized using APIs such as `gsk_render_node_serialize()` and `gsk_render_node_deserialize()`. The intended use for this is development - primarily the development of GTK - by allowing things such as creating testsuites and benchmarks, exchanging nodes in bug reports. GTK includes the `gtk4-node-editor` application for creating such test files.

The format is a text format that follows the CSS syntax rules. In particular, this means that every array of bytes will produce a render node when parsed, as there is a defined error recovery method. For more details on error handling, please refer to the documentation of the parsing APIs.

The grammar of a node text representation using the CSS value definition syntax looks like this:

    document: <@-rule>*<node>
    @-rule: `cicp` "name" { <property>* }
    node: container [ "name" ] { <document> } | <node-type> [ "name" ] { <property>* } | "name"
    property: <property-name>: <node> | <value> ;

Each node has its own `<node-type>` and supports a custom set of properties, each with their own `<property-name>` and syntax. The following paragraphs document each of the nodes and their properties.

When serializing and the value of a property equals the default value, this value will not be serialized. Serialization aims to produce an output as small as possible.

To embed newlines in strings, use \A. To break a long string into multiple lines, escape the newline with a .

# Names

### Nodes

Nodes can be given a name by adding a string after the `<node-type>` in their definition. That same node can then be used further down in the document by specifying just the name identifying the node.

### Textures

Just like nodes, textures can be referenced by name. When defining a named texture, the name has to be placed in front of the URL.

# Color states

Color states are represented either by an ident (for builtin ones) or a string (for custom ones):

    color-state: <ident> | <string>

Custom color states can be defined at the beginning of the document, with an @‌cicp rule.

The format for @‌cicp rules is

    @‌cicp "name" {
      ...
    }

The following properties can be set for custom color states:

property | syntax | default | printed
--- | --- | --- | ---
primaries | `<integer>` | 2 | always
transfer | `<integer>` | 2 | always
matrix | `<integer>` | 2 | always
range | `<range>` | full | non-default

Note that the primaries, transfer and matrix properties always need to be specified, since GTK does not allow creating color state objects with these being set to 2 (== unspecified).

Range can have the following values:

    range: narrow | full

# Colors

Colors can be specified with a variation of the modern CSS color syntax:

    color(<color-state> <number> <number> <number> ["/" <number>])

The traditional syntax for sRGB colors still works as well:

    rgba(<number>, <number>, <number>, <number)
    rgb(<number, <number>, <number>)

# Rectangles

Rectangles can be specified just as four integers for x, y, width and height:

    rect: <number> <number> <number> <number>

Rounded rectangles use a CSS-like syntax:

    rounded-rect: <rect> [ "/" <number>{1,4} [ "/" <number>{1,4} ] ]

# Nodes

### container

The container node is a special node that allows specifying a list of child nodes. Its contents follow the same rules as an empty document.

### blend

property | syntax | default | printed
--- | --- | --- | ---
bottom | `<node>` | color { } | always
mode | `<blend-mode>` | normal | non-default
top | `<node>` | color { } | always

Creates a node like `gsk_blend_node_new()` with the given properties.

Possible values for the mode property are:

    blend-mode: normal | multiply | screen | overlay | darken |
                lighten | color-dodge | color-burn | hard-light |
                soft-light | difference | exclusion | color |
                hue | saturation | luminosity

### blur

property | syntax | default | printed
--- | --- | --- | ---
blur | `<number>` | 1 | non-default
child | `<node>` | color { } | always

Creates a node like `gsk_blur_node_new()` with the given properties.

### border

property | syntax | default | printed
--- | --- | --- | ---
colors | `<color>{1,4}` | black | non-default
outline | `<rounded-rect>` | 50 | always
widths | `<number>{1,4}` | 1 | non-default

Creates a node like `gsk_border_node_new()` with the given properties.

For the color and width properties, the values follow the typical CSS order of top, right, bottom, left. If the last/left value isn’t given, the 2nd/right value is used. If the 3rd/bottom value isn’t given, the 1st/top value is used. And if the 2nd/right value also isn’t given, the 1st/top value is used for every 4 values.

### cairo

property | syntax | default | printed
--- | --- | --- | ---
bounds | `<rect>` | none | always
pixels | `<url>` | none | non-default
script | `<url>` | none | non-default

The pixels are a base64-encoded data url of png data. The script is a base64-encoded data url of a cairo script.

### clip

property | syntax | default | printed
--- | --- | --- | ---
child | `<node>` | color { } | always
clip | `<rounded-rect>` | 50 | always

Creates a node like `gsk_clip_node_new()` with the given properties.

As an extension, this node allows specifying a rounded rectangle for the clip property. If that rectangle is indeed rounded, a node like `gsk_rounded_clip_node_new()` will be created instead.

### color

property | syntax | default | printed
--- | --- | --- | ---
bounds | `<rect>` | 50 | always
color | `<color>` | `FF00CC` | always

Creates a node like `gsk_color_node_new()` with the given properties.

The color is chosen as an error pink so it is visible while also reminding people to change it.

### color-matrix

property | syntax | default | printed
--- | --- | --- | ---
child | `<node>` | color { } | always
matrix | `<transform>` | none | non-default
offset | `<number>{4}` | 0 0 0 0 | non-default

Creates a node like `gsk_color_matrix_node_new()` with the given properties.

The matrix property accepts a for compatibility purposes, but you should be aware that the allowed values are meant to be used on 3D transformations, so their naming might appear awkward. However, it is always possible to use the `matrix3d()` production to specify all 16 values individually.

### conic-gradient

property | syntax | default | printed
--- | --- | --- | ---
bounds | `<rect>` | 50 | always
center | `<point>` | 25, 25 | always
rotation | `<number>` | 0 | always
stops | `<color-stop>` | 0 `AF0`, 1 `F0C` | always
interpolation | `<color-state>` | srgb | non-default
hue-interpolation | `<hue-interp>` | shorter | non-default

Creates a node like `gsk_conic_gradient_node_new()` with the given properties.

Possible values for the hue-interpolation property are:

    hue-interpolation: shorter | longer | increasing | decreasing

### cross-fade

property | syntax | default | printed
--- | --- | --- | ---
end | `<node>` | color { } | always
progress | `<number>` | 0.5 | non-default
start | `<node>` | color { } | always

Creates a node like `gsk_cross_fade_node_new()` with the given properties.

### debug

property | syntax | default | printed
--- | --- | --- | ---
child | `<node>` | color { } | always
message | `<string>` | “” | non-default

Creates a node like `gsk_debug_node_new()` with the given properties.

### fill

property | syntax | default | printed
--- | --- | --- | ---
child | `<node>` | see below | always
path | `<string>` | “” | always
fill-rule | `<fill-rule>` | winding | always

Creates a node like `gsk_fill_node_new()` with the given properties.

The default child node is the default color node, but created with the bounds of the path.

Possible values for the fill-rule property are:

    fill-rule: winding | even-odd

### glshader

property | syntax | default | printed
--- | --- | --- | ---
bounds | `<rect>` | 50 | always
sourcecode | `<string>` | “” | always
args | `<uniform values>` | none | non-default
child1 | `<node>` | none | non-default
child2 | `<node>` | none | non-default
child3 | `<node>` | none | non-default
child4 | `<node>` | none | non-default

Creates a GLShader node. The `sourcecode` must be a GLSL fragment shader. The `args` must match the uniforms of simple types declared in that shader, in order and comma-separated. The `child` properties must match the sampler uniforms in the shader.

### inset-shadow

property | syntax | default | printed
--- | --- | --- | ---
blur | `<number>` | 0 | non-default
color | `<color>` | black | non-default
dx | `<number>` | 1 | non-default
dy | `<number>` | 1 | non-default
outline | `<rounded-rect>` | 50 | always
spread | `<number>` | 0 | non-default

Creates a node like `gsk_inset_shadow_node_new()` with the given properties.

### linear-gradient

property | syntax | default | printed
--- | --- | --- | ---
bounds | `<rect>` | 50 | always
start | `<point>` | 0 0 | always
end | `<point>` | 0 50 | always
stops | `<color-stop>` | 0 `AF0`, 1 `F0C` | always
interpolation | `<color-state>` | srgb | non-default
hue-interpolation | `<hue-interp>` | shorter | non-default

Creates a node like `gsk_linear_gradient_node_new()` with the given properties.

### mask

property | syntax | default | printed
--- | --- | --- | ---
source | `<node>` | color { } | always
mode | `<mask-mode>` | alpha | non-default
mask | `<node>` | color { } | always

Creates a node like `gsk_mask_node_new()` with the given properties.

Possible values for the mode property are:

    mask-mode: alpha | inverted-alpha | luminance | inverted-luminance

### opacity

property | syntax | default | printed
--- | --- | --- | ---
child | `<node>` | color { } | always
opacity | `<number>` | 0.5 | non-default

Creates a node like `gsk_transform_node_new()` with the given properties.

### outset-shadow

property | syntax | default | printed
--- | --- | --- | ---
blur | `<number>` | 0 | non-default
color | `<color>` | black | non-default
dx | `<number>` | 1 | non-default
dy | `<number>` | 1 | non-default
outline | `<rounded-rect>` | 50 | always
spread | `<number>` | 0 | non-default

Creates a node like `gsk_outset_shadow_node_new()` with the given properties.

### radial-gradient

property | syntax | default | printed
--- | --- | --- | ---
bounds | `<rect>` | 50 | always
center | `<point>` | 25 25 | always
hradius | `<number>` | 25 | always
vradius | `<number>` | 25 | always
start | `<number>` | 0 | always
end | `<number>` | 1 | always
stops | `<color-stop>` | 0 `AF0`, 1 `F0C` | always
interpolation | `<color-state>` | srgb | non-default
hue-interpolation | `<hue-interp>` | shorter | non-default

Creates a node like `gsk_radial_gradient_node_new()` with the given properties.

### repeat

property | syntax | default | printed
--- | --- | --- | ---
bounds | `<rect>` | bounds of child node | non-default
child | `<node>` | color { } | always
child-bounds | `<rect>` | bounds of child node | non-default

Creates a node like `gsk_repeat_node_new()` with the given properties.

### repeating-linear-gradient

property | syntax | default | printed
--- | --- | --- | ---
bounds | `<rect>` | 50 | always
start | `<point>` | 0 0 | always
end | `<point>` | 0 50 | always
stops | `<color-stop>` | 0 `AF0`, 1 `F0C` | always

Creates a node like `gsk_repeating_linear_gradient_node_new()` with the given properties.

### repeating radial-gradient

property | syntax | default | printed
--- | --- | --- | ---
bounds | `<rect>` | 50 | always
center | `<point>` | 25 25 | always
hradius | `<number>` | 25 | always
vradius | `<number>` | 25 | always
start | `<number>` | 0 | always
end | `<number>` | 1 | always
stops | `<color-stop>` | 0 `AF0`, 1 `F0C` | always

Creates a node like `gsk_repeating_radial_gradient_node_new()` with the given properties.

### rounded-clip

property | syntax | default | printed
--- | --- | --- | ---
child | `<node>` | color { } | always
clip | `<rounded-rect>` | 50 | always

Creates a node like `gsk_rounded_clip_node_new()` with the given properties.

### shadow

property | syntax | default | printed
--- | --- | --- | ---
child | `<node>` | color { } | always
shadows | `<shadow>` | black 1 1 | always

Creates a node like `gsk_shadow_node_new()` with the given properties.

### stroke

property | syntax | default | printed
--- | --- | --- | ---
child | `<node>` | see below | always
path | `<string>` | “” | always
line-width | `<number>` | 0 | non-default
line-cap | `<line-cap>` | butt | always
line-join | `<line-join>` | miter | always
miter-limit | `<number>` | 4 | non-default
dash | `<number>{+}|none` | none | non-default
dash-offset | `<number>` | 0 | non-default

Creates a node like `gsk_stroke_node_new()` with the given properties.

The default child node is the default color node, but created with the stroke bounds of the path.

Possible values for the line-cap property are:

    line-cap: butt | round | square

Possible values for the line-join property are:

    line-join: miter | round | bevel

### text

property | syntax | default | printed
--- | --- | --- | ---
color | `<color>` | black | non-default
font | `<string>` `<url>`? | “Cantarell 15px” | always
glyphs | `<glyphs>` | “Hello” | always
offset | `<point>` | 0 0 | non-default
hint-style | `<hint-style>` | slight | non-default
antialias | `<antialias>` | gray | non-default
hint-metrics | `<hint-metrics>` | off | non-default

Creates a node like `gsk_text_node_new()` with the given properties.

If a url is specified for the font, it must point to a font file for the font that is specified in the string. It can be either a data url containing a base64-encoded font file, or a regular url that points to a font file.

Glyphs can be specified as an ASCII string, or as a comma-separated list of their glyph IDs. Optionally, the advance width, x and y offsets and flags can be specified as well, like this: 40 10 0 0 color.

If the given font does not exist or the given glyphs are invalid for the given font, an error node will be returned.

Possible values for the hint-style property are:

    hint-style: none | slight | full

Possible value for the antialias property are:

    antialias:  none | gray

Possible value for hint-metrics are:

    hint-metrics:  on | off

### texture

property | syntax | default | printed
--- | --- | --- | ---
bounds | `<rect>` | 50 | always
texture | `<string>`?`<url>`? | see below | always

Creates a node like `gsk_texture_node_new()` with the given properties.

If a string is specified for the texture, it will be used as a name for the text. Textures can be reused by specifying the name of a previously used texture. In that case, the url can be omitted.

The default texture is a 10x10 checkerboard with the top left and bottom right 5x5 being in the color `FF00CC` and the other part being transparent. A possible representation for this texture is `url("data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAAoAAAAKCAYAAACNMs+9AAAABmJLR0QA/wD/AP+gvaeTAAAAKUlEQVQYlWP8z3DmPwMaYGQwYUQXY0IXwAUGUCGGoxkYGBiweXAoeAYAz44F3e3U1xUAAAAASUVORK5CYII=")`.

### texture-scale

property | syntax | default | printed
--- | --- | --- | ---
bounds | `<rect>` | 50 | always
texture | `<url>` | see below | always
filter | `filter` | linear | non-default

Creates a node like `gsk_texture_scale_node_new()` with the given properties.

The default texture is a 10x10 checkerboard, just like for texture.

Possible values for the filter property are:

    filter: linear | nearest | trilinear

### transform

property | syntax | default | printed
--- | --- | --- | ---
child | `<node>` | color { } | always
transform | `<transform>` | none | non-default

Creates a node like `gsk_transform_node_new()` with the given properties.