The blend modes available for render nodes.

The implementation of each blend mode is deferred to the rendering pipeline.

See <https://www.w3.org/TR/compositing-1/#blending> for more information on blending and blend modes.

The corner indices used by [gsk.rounded_rect.RoundedRect].

[gsk.types.FillRule] is used to select how paths are filled.

Whether or not a point is included in the fill is determined by taking a ray from that point to infinity and looking at intersections with the path. The ray can be in any direction, as long as it doesn't pass through the end point of a segment or have a tricky intersection such as intersecting tangent to the path.

(Note that filling is not actually implemented in this way. This is just a description of the rule that is applied.)

New entries may be added in future versions.

This defines the types of the uniforms that GskGLShaders declare.

It defines both what the type is called in the GLSL shader code, and what the corresponding C type is on the Gtk side.

Specifies how to render the start and end points of contours or dashes when stroking.

The default line cap style is [gsk.types.LineCap.Butt].

New entries may be added in future versions.

Specifies how to render the junction of two lines when stroking.

The default line join style is [gsk.types.LineJoin.Miter].

New entries may be added in future versions.

The mask modes available for mask nodes.

The values of the [gsk.types.PathDirection] enum are used to pick one of the four tangents at a given point on the path.

Note that the directions for @GSK_PATH_FROM_START/@GSK_PATH_TO_END and @GSK_PATH_TO_START/@GSK_PATH_FROM_END will coincide for smooth points. Only sharp turns will exhibit four different directions.

Flags that can be passed to [gsk.path.Path.foreach_] to influence what kinds of operations the path is decomposed into.

By default, [gsk.path.Path.foreach_] will only emit a path with all operations flattened to straight lines to allow for maximum compatibility. The only operations emitted will be [gsk.types.PathOperation.Move], [gsk.types.PathOperation.Line] and [gsk.types.PathOperation.Close].

Path operations are used to describe the segments of a [gsk.path.Path].

More values may be added in the future.

The type of a node determines what the node is rendering.

The filters used when scaling texture data.

The actual implementation of each filter is deferred to the rendering pipeline.

Errors that can happen during (de)serialization.

The categories of matrices relevant for GSK and GTK.

Note that any category includes matrices of all later categories. So if you want to for example check if a matrix is a 2D matrix, category >= GSK_TRANSFORM_CATEGORY_2D is the way to do this.

Also keep in mind that rounding errors may cause matrices to not conform to their categories. Otherwise, matrix operations done via multiplication will not worsen categories. So for the matrix multiplication C = A * B, category(C) = MIN (category(A), category(B)).

A render node applying a blending function between its two child nodes.

A render node applying a blur effect to its single child.

A render node for a border.

A render node for a Cairo surface.

A GSK renderer that is using cairo.

Since it is using cairo, this renderer cannot support 3D transformations.

A render node applying a rectangular clip to its single child node.

A render node controlling the color matrix of its single child node.

A render node for a solid color.

A color stop in a gradient node.

A render node for a conic gradient.

A render node that can contain other render nodes.

A render node cross fading between two child nodes.

A render node that emits a debugging message when drawing its child node.

A render node filling the area given by [gsk.path.Path] and [gsk.types.FillRule] with the child node.

A [gsk.glshader.GLShader] is a snippet of GLSL that is meant to run in the fragment shader of the rendering pipeline.

A fragment shader gets the coordinates being rendered as input and produces the pixel values for that particular pixel. Additionally, the shader can declare a set of other input arguments, called uniforms (as they are uniform over all the calls to your shader in each instance of use). A shader can also receive up to 4 textures that it can use as input when producing the pixel data.

[gsk.glshader.GLShader] is usually used with [gtk.snapshot.Snapshot.pushGlShader] to produce a [gsk.glshader_node.GLShaderNode] in the rendering hierarchy, and then its input textures are constructed by rendering the child nodes to textures before rendering the shader node itself. (You can pass texture nodes as children if you want to directly use a texture as input).

The actual shader code is GLSL code that gets combined with some other code into the fragment shader. Since the exact capabilities of the GPU driver differs between different OpenGL drivers and hardware, GTK adds some defines that you can use to ensure your GLSL code runs on as many drivers as it can.

If the OpenGL driver is GLES, then the shader language version is set to 100, and GSK_GLES will be defined in the shader.

Otherwise, if the OpenGL driver does not support the 3.2 core profile, then the shader will run with language version 110 for GL2 and 130 for GL3, and GSK_LEGACY will be defined in the shader.

If the OpenGL driver supports the 3.2 code profile, it will be used, the shader language version is set to 150, and GSK_GL3 will be defined in the shader.

The main function the shader must implement is:

void mainImage(out vec4 fragColor,
               in vec2 fragCoord,
               in vec2 resolution,
               in vec2 uv)

Where the input @fragCoord is the coordinate of the pixel we're currently rendering, relative to the boundary rectangle that was specified in the [gsk.glshader_node.GLShaderNode], and @resolution is the width and height of that rectangle. This is in the typical GTK coordinate system with the origin in the top left. @uv contains the u and v coordinates that can be used to index a texture at the corresponding point. These coordinates are in the [0..1]x[0..1] region, with 0, 0 being in the lower left corder (which is typical for OpenGL).

The output @fragColor should be a RGBA color (with premultiplied alpha) that will be used as the output for the specified pixel location. Note that this output will be automatically clipped to the clip region of the glshader node.

In addition to the function arguments the shader can define up to 4 uniforms for textures which must be called u_textureN (i.e. u_texture1 to u_texture4) as well as any custom uniforms you want of types int, uint, bool, float, vec2, vec3 or vec4.

All textures sources contain premultiplied alpha colors, but if some there are outer sources of colors there is a gsk_premultiply() helper to compute premultiplication when needed.

Note that GTK parses the uniform declarations, so each uniform has to be on a line by itself with no other code, like so:

uniform float u_time;
uniform vec3 u_color;
uniform sampler2D u_texture1;
uniform sampler2D u_texture2;

GTK uses the "gsk" namespace in the symbols it uses in the shader, so your code should not use any symbols with the prefix gsk or GSK. There are some helper functions declared that you can use:

vec4 GskTexture(sampler2D sampler, vec2 texCoords);

This samples a texture (e.g. u_texture1) at the specified coordinates, and contains some helper ifdefs to ensure that it works on all OpenGL versions.

You can compile the shader yourself using [gsk.glshader.GLShader.compile], otherwise the GSK renderer will do it when it handling the glshader node. If errors occurs, the returned @error will include the glsl sources, so you can see what GSK was passing to the compiler. You can also set GSK_DEBUG=shaders in the environment to see the sources and other relevant information about all shaders that GSK is handling.

An example shader

uniform float position;
uniform sampler2D u_texture1;
uniform sampler2D u_texture2;

void mainImage(out vec4 fragColor,
              in vec2 fragCoord,
              in vec2 resolution,
              in vec2 uv) {
 vec4 source1 = GskTexture(u_texture1, uv);
 vec4 source2 = GskTexture(u_texture2, uv);

 fragColor = position * source1 + (1.0 - position) * source2;
}

A render node using a GL shader when drawing its children nodes.

A render node for an inset shadow.

A render node for a linear gradient.

A render node masking one child node with another.

A render node controlling the opacity of its single child node.

A render node for an outset shadow.

A location in a parse buffer.

A [gsk.path.Path] describes lines and curves that are more complex than simple rectangles.

Paths can used for rendering (filling or stroking) and for animations (e.g. as trajectories).

[gsk.path.Path] is an immutable, opaque, reference-counted struct. After creation, you cannot change the types it represents. Instead, new [gsk.path.Path] objects have to be created. The [gsk.path_builder.PathBuilder] structure is meant to help in this endeavor.

Conceptually, a path consists of zero or more contours (continuous, connected curves), each of which may or may not be closed. Contours are typically constructed from Bézier segments.

[gsk.path_builder.PathBuilder] is an auxiliary object for constructing [gsk.path.Path] objects.

A path is constructed like this:

GskPath *
construct_path (void)
{
 GskPathBuilder *builder;

 builder = gsk_path_builder_new ();

 // add contours to the path here

 return gsk_path_builder_free_to_path (builder);

Adding contours to the path can be done in two ways. The easiest option is to use the gsk_path_builder_add_* group of functions that add predefined contours to the current path, either common shapes like [gsk.path_builder.PathBuilder.addCircle] or by adding from other paths like [gsk.path_builder.PathBuilder.addPath].

The gsk_path_builder_add_* methods always add complete contours, and do not use or modify the current point.

The other option is to define each line and curve manually with the gsk_path_builder_*_to group of functions. You start with a call to [gsk.path_builder.PathBuilder.moveTo] to set the starting point and then use multiple calls to any of the drawing functions to move the pen along the plane. Once you are done, you can call [gsk.path_builder.PathBuilder.close] to close the path by connecting it back with a line to the starting point.

This is similar to how paths are drawn in Cairo.

Note that [gsk.path_builder.PathBuilder] will reduce the degree of added Bézier curves as much as possible, to simplify rendering.

[gsk.path_measure.PathMeasure] is an object that allows measurements on [gsk.path.Path]s such as determining the length of the path.

Many measuring operations require sampling the path length at intermediate points. Therefore, a [gsk.path_measure.PathMeasure] has a tolerance that determines what precision is required for such approximations.

A [gsk.path_measure.PathMeasure] struct is a reference counted struct and should be treated as opaque.

[gsk.path_point.PathPoint] is an opaque type representing a point on a path.

It can be queried for properties of the path at that point, such as its tangent or its curvature.

To obtain a [gsk.path_point.PathPoint], use [gsk.path.Path.getClosestPoint], [gsk.path.Path.getStartPoint], [gsk.path.Path.getEndPoint] or [gsk.path_measure.PathMeasure.getPoint].

Note that [gsk.path_point.PathPoint] structs are meant to be stack-allocated, and don't hold a reference to the path object they are obtained from. It is the callers responsibility to keep a reference to the path as long as the [gsk.path_point.PathPoint] is used.

A render node for a radial gradient.

[gsk.render_node.RenderNode] is the basic block in a scene graph to be rendered using [gsk.renderer.Renderer].

Each node has a parent, except the top-level node; each node may have children nodes.

Each node has an associated drawing surface, which has the size of the rectangle set when creating it.

Render nodes are meant to be transient; once they have been associated to a [gsk.renderer.Renderer] it's safe to release any reference you have on them. All [gsk.render_node.RenderNode]s are immutable, you can only specify their properties during construction.

[gsk.renderer.Renderer] is a class that renders a scene graph defined via a tree of [gsk.render_node.RenderNode] instances.

Typically you will use a [gsk.renderer.Renderer] instance to repeatedly call [gsk.renderer.Renderer.render] to update the contents of its associated [gdk.surface.Surface].

It is necessary to realize a [gsk.renderer.Renderer] instance using [gsk.renderer.Renderer.realize] before calling [gsk.renderer.Renderer.render], in order to create the appropriate windowing system resources needed to render the scene.

A render node repeating its single child node.

A render node for a repeating linear gradient.

A render node for a repeating radial gradient.

A render node applying a rounded rectangle clip to its single child.

A rectangular region with rounded corners.

Application code should normalize rectangles using [gsk.rounded_rect.RoundedRect.normalize]; this function will ensure that the bounds of the rectangle are normalized and ensure that the corner values are positive and the corners do not overlap.

All functions taking a [gsk.rounded_rect.RoundedRect] as an argument will internally operate on a normalized copy; all functions returning a [gsk.rounded_rect.RoundedRect] will always return a normalized one.

The algorithm used for normalizing corner sizes is described in

An object to build the uniforms data for a [gsk.glshader.GLShader].

The shadow parameters in a shadow node.

A render node drawing one or more shadows behind its single child node.

A [gsk.stroke.Stroke] struct collects the parameters that influence the operation of stroking a path.

A render node that will fill the area determined by stroking the the given [gsk.path.Path] using the [gsk.stroke.Stroke] attributes.

A render node that potentially diverts a part of the scene graph to a subsurface.

A render node drawing a set of glyphs.

A render node for a [gdk.texture.Texture].

A render node for a [gdk.texture.Texture].

[gsk.transform.Transform] is an object to describe transform matrices.

Unlike [graphene.matrix.Matrix], [gsk.transform.Transform] retains the steps in how a transform was constructed, and allows inspecting them. It is modeled after the way CSS describes transforms.

[gsk.transform.Transform] objects are immutable and cannot be changed after creation. This means code can safely expose them as properties of objects without having to worry about others changing them.

A render node applying a [gsk.transform.Transform] to its single child node.

A GSK renderer that is using Vulkan.

This renderer will fail to realize if Vulkan is not supported.