GskGLShader

GskGLShader — Fragment shaders for GSK

Properties

char * resource Read / Write / Construct Only
GBytes * source Read / Write / Construct Only

Types and Values

Object Hierarchy

    GObject
    ╰── GskGLShader

Description

A GskGLShader 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.

GskGLShader is usually used with gtk_snapshot_push_gl_shader() to produce a GskGLShaderNode 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:

1
2
3
4
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 GskGLShaderNode, 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:

1
2
3
4
uniform float u_time;
uniform vec3 u_color;
uniform sampler2D u_texture1;
uniform sampler2D u_texture2;

GTK uses the 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:

1
vec4 GskTexture(sampler2D sampler, vec2 texCoords);

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

You can compile the shader yourself using gsk_gl_shader_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

1
2
3
4
5
6
7
8
9
10
11
12
13
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;
}

Functions

gsk_gl_shader_new_from_bytes ()

GskGLShader *
gsk_gl_shader_new_from_bytes (GBytes *sourcecode);

Creates a GskGLShader that will render pixels using the specified code.

Parameters

sourcecode

GLSL sourcecode for the shader, as a GBytes

 

Returns

A new GskGLShader.

[transfer full]


gsk_gl_shader_new_from_resource ()

GskGLShader *
gsk_gl_shader_new_from_resource (const char *resource_path);

Creates a GskGLShader that will render pixels using the specified code.

Parameters

resource_path

path to a resource that contains the GLSL sourcecode for the shader

 

Returns

A new GskGLShader.

[transfer full]


gsk_gl_shader_compile ()

gboolean
gsk_gl_shader_compile (GskGLShader *shader,
                       GskRenderer *renderer,
                       GError **error);

Tries to compile the shader for the given renderer , and reports FALSE with an error if there is a problem. You should use this function before relying on the shader for rendering and use a fallback with a simpler shader or without shaders if it fails.

Note that this will modify the rendering state (for example change the current GL context) and requires the renderer to be set up. This means that the widget has to be realized. Commonly you want to call this from the realize signal of a widget, or during widget snapshot.

Parameters

shader

a GskGLShader

 

renderer

a GskRenderer

 

error

location to store error in

 

Returns

TRUE on success, FALSE if an error occurred


gsk_gl_shader_get_source ()

GBytes *
gsk_gl_shader_get_source (GskGLShader *shader);

Gets the GLSL sourcecode being used to render this shader.

Parameters

shader

a GskGLShader

 

Returns

The source code for the shader.

[transfer none]


gsk_gl_shader_get_n_textures ()

int
gsk_gl_shader_get_n_textures (GskGLShader *shader);

Returns the number of textures that the shader requires.

This can be used to check that the a passed shader works in your usecase. It is determined by looking at the highest u_textureN value that the shader defines.

Parameters

shader

a GskGLShader

 

Returns

The number of texture inputs required by shader


gsk_gl_shader_get_n_uniforms ()

int
gsk_gl_shader_get_n_uniforms (GskGLShader *shader);

Get the number of declared uniforms for this shader.

Parameters

shader

a GskGLShader

 

Returns

The number of declared uniforms


gsk_gl_shader_get_uniform_name ()

const char *
gsk_gl_shader_get_uniform_name (GskGLShader *shader,
                                int idx);

Get the name of the declared uniform for this shader at index idx .

Parameters

shader

a GskGLShader

 

idx

index of the uniform

 

Returns

The name of the declared uniform.

[transfer none]


gsk_gl_shader_find_uniform_by_name ()

int
gsk_gl_shader_find_uniform_by_name (GskGLShader *shader,
                                    const char *name);

Looks for a uniform by the name name , and returns the index of the uniform, or -1 if it was not found.

Parameters

shader

a GskGLShader

 

name

uniform name

 

Returns

The index of the uniform, or -1


gsk_gl_shader_get_uniform_type ()

GskGLUniformType
gsk_gl_shader_get_uniform_type (GskGLShader *shader,
                                int idx);

Get the type of the declared uniform for this shader at index idx .

Parameters

shader

a GskGLShader

 

idx

index of the uniform

 

Returns

The type of the declared uniform


gsk_gl_shader_get_uniform_offset ()

int
gsk_gl_shader_get_uniform_offset (GskGLShader *shader,
                                  int idx);

Get the offset into the data block where data for this uniforms is stored.

Parameters

shader

a GskGLShader

 

idx

index of the uniform

 

Returns

The data offset


gsk_gl_shader_get_args_size ()

gsize
gsk_gl_shader_get_args_size (GskGLShader *shader);

Get the size of the data block used to specify arguments for this shader.

Parameters

shader

a GskGLShader

 

Returns

The size of the data block


gsk_gl_shader_get_arg_float ()

float
gsk_gl_shader_get_arg_float (GskGLShader *shader,
                             GBytes *args,
                             int idx);

Gets the value of the uniform idx in the args block. The uniform must be of float type.

Parameters

shader

a GskGLShader

 

args

uniform arguments

 

idx

index of the uniform

 

Returns

The value


gsk_gl_shader_get_arg_int ()

gint32
gsk_gl_shader_get_arg_int (GskGLShader *shader,
                           GBytes *args,
                           int idx);

Gets the value of the uniform idx in the args block. The uniform must be of int type.

Parameters

shader

a GskGLShader

 

args

uniform arguments

 

idx

index of the uniform

 

Returns

The value


gsk_gl_shader_get_arg_uint ()

guint32
gsk_gl_shader_get_arg_uint (GskGLShader *shader,
                            GBytes *args,
                            int idx);

Gets the value of the uniform idx in the args block. The uniform must be of uint type.

Parameters

shader

a GskGLShader

 

args

uniform arguments

 

idx

index of the uniform

 

Returns

The value


gsk_gl_shader_get_arg_bool ()

gboolean
gsk_gl_shader_get_arg_bool (GskGLShader *shader,
                            GBytes *args,
                            int idx);

Gets the value of the uniform idx in the args block. The uniform must be of bool type.

Parameters

shader

a GskGLShader

 

args

uniform arguments

 

idx

index of the uniform

 

Returns

The value


gsk_gl_shader_get_arg_vec2 ()

void
gsk_gl_shader_get_arg_vec2 (GskGLShader *shader,
                            GBytes *args,
                            int idx,
                            graphene_vec2_t *out_value);

Gets the value of the uniform idx in the args block. The uniform must be of vec2 type.

Parameters

shader

a GskGLShader

 

args

uniform arguments

 

idx

index of the uniform

 

out_value

location to store the uniform value in

 

gsk_gl_shader_get_arg_vec3 ()

void
gsk_gl_shader_get_arg_vec3 (GskGLShader *shader,
                            GBytes *args,
                            int idx,
                            graphene_vec3_t *out_value);

Gets the value of the uniform idx in the args block. The uniform must be of vec3 type.

Parameters

shader

a GskGLShader

 

args

uniform arguments

 

idx

index of the uniform

 

out_value

location to store the uniform value in

 

gsk_gl_shader_get_arg_vec4 ()

void
gsk_gl_shader_get_arg_vec4 (GskGLShader *shader,
                            GBytes *args,
                            int idx,
                            graphene_vec4_t *out_value);

Gets the value of the uniform idx in the args block. The uniform must be of vec4 type.

Parameters

shader

a GskGLShader

 

args

uniform arguments

 

idx

index of the uniform

 

out_value

location to store set the uniform value in

 

gsk_gl_shader_format_args_va ()

GBytes *
gsk_gl_shader_format_args_va (GskGLShader *shader,
                              va_list uniforms);

Formats the uniform data as needed for feeding the named uniforms values into the shader. The argument list is a list of pairs of names, and values for the types that match the declared uniforms (i.e. double/int/guint/gboolean for primitive values and graphene_vecN_t * for vecN uniforms).

It is an error to pass a uniform name that is not declared by the shader.

Any uniforms of the shader that are not included in the argument list are zero-initialized.

Parameters

shader

a GskGLShader

 

uniforms

name-Value pairs for the uniforms of shader , ending with a NULL name

 

Returns

A newly allocated block of data which can be passed to gsk_gl_shader_node_new().

[transfer full]


gsk_gl_shader_format_args ()

GBytes *
gsk_gl_shader_format_args (GskGLShader *shader,
                           ...);

Formats the uniform data as needed for feeding the named uniforms values into the shader. The argument list is a list of pairs of names, and values for the types that match the declared uniforms (i.e. double/int/guint/gboolean for primitive values and graphene_vecN_t * for vecN uniforms).

Any uniforms of the shader that are not included in the argument list are zero-initialized.

Parameters

shader

a GskGLShader

 

...

name-Value pairs for the uniforms of shader , ending with a NULL name

 

Returns

A newly allocated block of data which can be passed to gsk_gl_shader_node_new().

[transfer full]


gsk_shader_args_builder_new ()

GskShaderArgsBuilder *
gsk_shader_args_builder_new (GskGLShader *shader,
                             GBytes *initial_values);

gsk_shader_args_builder_to_args ()

GBytes *
gsk_shader_args_builder_to_args (GskShaderArgsBuilder *builder);

Creates a new GBytes args from the current state of the given builder . Any uniforms of the shader that have not been explicitly set on the builder are zero-initialized.

The given GskShaderArgsBuilder is reset once this function returns; you cannot call this function multiple times on the same builder instance.

This function is intended primarily for bindings. C code should use gsk_shader_args_builder_free_to_args().

Parameters

builder

a GskShaderArgsBuilder

 

Returns

the newly allocated builder, free with gsk_shader_args_builder_free().

[transfer full]


gsk_shader_args_builder_free_to_args ()

GBytes *
gsk_shader_args_builder_free_to_args (GskShaderArgsBuilder *builder);

gsk_shader_args_builder_unref ()

void
gsk_shader_args_builder_unref (GskShaderArgsBuilder *builder);

Decreases the reference count of a GskShaderArgBuilder by one. If the resulting reference count is zero, frees the builder.

Parameters

builder

a GskShaderArgsBuilder

 

gsk_shader_args_builder_ref ()

GskShaderArgsBuilder *
gsk_shader_args_builder_ref (GskShaderArgsBuilder *builder);

Increases the reference count of a GskShaderArgsBuilder by one.

Parameters

builder

a GskShaderArgsBuilder

 

Returns

the passed in GskShaderArgsBuilder


gsk_shader_args_builder_set_float ()

void
gsk_shader_args_builder_set_float (GskShaderArgsBuilder *builder,
                                   int idx,
                                   float value);

Sets the value of the uniform idx . The uniform must be of float type.

Parameters

builder

a GskShaderArgsBuilder

 

idx

index of the uniform

 

value

value to set the uniform to

 

gsk_shader_args_builder_set_int ()

void
gsk_shader_args_builder_set_int (GskShaderArgsBuilder *builder,
                                 int idx,
                                 gint32 value);

Sets the value of the uniform idx . The uniform must be of int type.

Parameters

builder

a GskShaderArgsBuilder

 

idx

index of the uniform

 

value

value to set the uniform to

 

gsk_shader_args_builder_set_uint ()

void
gsk_shader_args_builder_set_uint (GskShaderArgsBuilder *builder,
                                  int idx,
                                  guint32 value);

Sets the value of the uniform idx . The uniform must be of uint type.

Parameters

builder

a GskShaderArgsBuilder

 

idx

index of the uniform

 

value

value to set the uniform to

 

gsk_shader_args_builder_set_bool ()

void
gsk_shader_args_builder_set_bool (GskShaderArgsBuilder *builder,
                                  int idx,
                                  gboolean value);

Sets the value of the uniform idx . The uniform must be of bool type.

Parameters

builder

a GskShaderArgsBuilder

 

idx

index of the uniform

 

value

value to set the uniform to

 

gsk_shader_args_builder_set_vec2 ()

void
gsk_shader_args_builder_set_vec2 (GskShaderArgsBuilder *builder,
                                  int idx,
                                  const graphene_vec2_t *value);

Sets the value of the uniform idx . The uniform must be of vec2 type.

Parameters

builder

A GskShaderArgsBuilder

 

idx

index of the uniform

 

value

value to set the uniform too

 

gsk_shader_args_builder_set_vec3 ()

void
gsk_shader_args_builder_set_vec3 (GskShaderArgsBuilder *builder,
                                  int idx,
                                  const graphene_vec3_t *value);

Sets the value of the uniform idx . The uniform must be of vec3 type.

Parameters

builder

a GskShaderArgsBuilder

 

idx

index of the uniform

 

value

value to set the uniform too

 

gsk_shader_args_builder_set_vec4 ()

void
gsk_shader_args_builder_set_vec4 (GskShaderArgsBuilder *builder,
                                  int idx,
                                  const graphene_vec4_t *value);

Sets the value of the uniform idx . The uniform must be of vec4 type.

Parameters

builder

a GskShaderArgsBuilder

 

idx

index of the uniform

 

value

value to set the uniform too

 

Types and Values

GskGLShader

typedef struct _GskGLShader GskGLShader;

GskShaderArgsBuilder

typedef struct _GskShaderArgsBuilder GskShaderArgsBuilder;

Property Details

The “resource” property

  “resource”                 char *

Resource containing the source code for the shader.

If the shader source is not coming from a resource, this will be NULL.

Owner: GskGLShader

Flags: Read / Write / Construct Only

Default value: NULL


The “source” property

  “source”                   GBytes *

The sourcecode for the shader.

Owner: GskGLShader

Flags: Read / Write / Construct Only