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Functions
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:
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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
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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.
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.
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.
gsk_gl_shader_get_source ()
GBytes *
gsk_gl_shader_get_source (GskGLShader *shader);
Gets the GLSL sourcecode being used to render this shader.
gsk_gl_shader_get_resource ()
const char *
gsk_gl_shader_get_resource (GskGLShader *shader);
Gets the resource path for the GLSL sourcecode being used to render this shader.
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.
gsk_gl_shader_get_n_uniforms ()
int
gsk_gl_shader_get_n_uniforms (GskGLShader *shader);
Get the number of declared uniforms for this shader.
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
.
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.
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
.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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);
Allocates a builder that can be used to construct a new uniform data chunk.
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().
gsk_shader_args_builder_free_to_args ()
GBytes *
gsk_shader_args_builder_free_to_args (GskShaderArgsBuilder *builder);
Creates a new GBytes args from the current state of the
given builder
, and frees the builder
instance. Any uniforms
of the shader that have not been explicitly set on the builder
are zero-initialized.
[skip]
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.
gsk_shader_args_builder_ref ()
GskShaderArgsBuilder *
gsk_shader_args_builder_ref (GskShaderArgsBuilder *builder);
Increases the reference count of a GskShaderArgsBuilder by one.
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.
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.
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.
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.
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.
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.
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.
Types and Values
enum GskGLUniformType
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.
GskShaderArgsBuilder
typedef struct _GskShaderArgsBuilder GskShaderArgsBuilder;
An object to build the uniforms data for a GskGLShader.