GLShader

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;
}

class GLShader : ObjectG {

static gsk.glshader.GLShader newFromBytes(glib.bytes.Bytes sourcecode);

static gsk.glshader.GLShader newFromResource(string resourcePath);

bool compile(gsk.renderer.Renderer renderer);

int findUniformByName(string name);

bool getArgBool(glib.bytes.Bytes args, int idx);

float getArgFloat(glib.bytes.Bytes args, int idx);

int getArgInt(glib.bytes.Bytes args, int idx);

uint getArgUint(glib.bytes.Bytes args, int idx);

void getArgVec2(glib.bytes.Bytes args, int idx, graphene.vec2.Vec2 outValue);

void getArgVec3(glib.bytes.Bytes args, int idx, graphene.vec3.Vec3 outValue);

void getArgVec4(glib.bytes.Bytes args, int idx, graphene.vec4.Vec4 outValue);

size_t getArgsSize();

int getNTextures();

int getNUniforms();

string getResource();

glib.bytes.Bytes getSource();

string getUniformName(int idx);

int getUniformOffset(int idx);

gsk.types.GLUniformType getUniformType(int idx);

}

Members

Functions

compile bool compile(gsk.renderer.Renderer renderer): Tries to compile the shader for the given renderer.
findUniformByName int findUniformByName(string name): Looks for a uniform by the name name, and returns the index of the uniform, or -1 if it was not found.
getArgBool bool getArgBool(glib.bytes.Bytes args, int idx): Gets the value of the uniform idx in the args block.
getArgFloat float getArgFloat(glib.bytes.Bytes args, int idx): Gets the value of the uniform idx in the args block.
getArgInt int getArgInt(glib.bytes.Bytes args, int idx): Gets the value of the uniform idx in the args block.
getArgUint uint getArgUint(glib.bytes.Bytes args, int idx): Gets the value of the uniform idx in the args block.
getArgVec2 void getArgVec2(glib.bytes.Bytes args, int idx, graphene.vec2.Vec2 outValue): Gets the value of the uniform idx in the args block.
getArgVec3 void getArgVec3(glib.bytes.Bytes args, int idx, graphene.vec3.Vec3 outValue): Gets the value of the uniform idx in the args block.
getArgVec4 void getArgVec4(glib.bytes.Bytes args, int idx, graphene.vec4.Vec4 outValue): Gets the value of the uniform idx in the args block.
getArgsSize size_t getArgsSize(): Get the size of the data block used to specify arguments for this shader.
getNTextures int getNTextures(): Returns the number of textures that the shader requires.
getNUniforms int getNUniforms(): Get the number of declared uniforms for this shader.
getResource string getResource(): Gets the resource path for the GLSL sourcecode being used to render this shader.
getSource glib.bytes.Bytes getSource(): Gets the GLSL sourcecode being used to render this shader.
getUniformName string getUniformName(int idx): Get the name of the declared uniform for this shader at index idx.
getUniformOffset int getUniformOffset(int idx): Get the offset into the data block where data for this uniforms is stored.
getUniformType gsk.types.GLUniformType getUniformType(int idx): Get the type of the declared uniform for this shader at index idx.

Static functions

newFromBytes gsk.glshader.GLShader newFromBytes(glib.bytes.Bytes sourcecode): Creates a gsk.glshader.GLShader that will render pixels using the specified code.
newFromResource gsk.glshader.GLShader newFromResource(string resourcePath): Creates a gsk.glshader.GLShader that will render pixels using the specified code.

Inherited Members

From ObjectG

setGObject void setGObject(void* cObj, Flag!"Take" take): Set the GObject of a D ObjectG wrapper.
cPtr void* cPtr(Flag!"Dup" dup): Get a pointer to the underlying C object.
ref_ void* ref_(void* gObj): Calls g_object_ref() on a GObject.
unref unref(void* gObj): Calls g_object_unref() on a GObject.
getType GType getType(): Get the GType of an object.
gType GType gType [@property getter]: GObject GType property.
self ObjectG self(): Convenience method to return this cast to a type. For use in D with statements.
getDObject T getDObject(void* cptr, Flag!"Take" take): Template to get the D object from a C GObject and cast it to the given D object type.
connectSignalClosure ulong connectSignalClosure(string signalDetail, DClosure closure, Flag!"After" after): Connect a D closure to an object signal.
setProperty void setProperty(string propertyName, T val): Template for setting a GObject property.
getProperty T getProperty(string propertyName): Template for getting a GObject property.
compatControl size_t compatControl(size_t what, void* data)
bindProperty gobject.binding.Binding bindProperty(string sourceProperty, gobject.object.ObjectG target, string targetProperty, gobject.types.BindingFlags flags): Creates a binding between source_property on source and target_property on target.
bindPropertyFull gobject.binding.Binding bindPropertyFull(string sourceProperty, gobject.object.ObjectG target, string targetProperty, gobject.types.BindingFlags flags, gobject.closure.Closure transformTo, gobject.closure.Closure transformFrom): Creates a binding between source_property on source and target_property on target, allowing you to set the transformation functions to be used by the binding.
forceFloating void forceFloating(): This function is intended for #GObject implementations to re-enforce a floating[floating-ref] object reference. Doing this is seldom required: all #GInitiallyUnowneds are created with a floating reference which usually just needs to be sunken by calling gobject.object.ObjectG.refSink.
freezeNotify void freezeNotify(): Increases the freeze count on object. If the freeze count is non-zero, the emission of "notify" signals on object is stopped. The signals are queued until the freeze count is decreased to zero. Duplicate notifications are squashed so that at most one #GObject::notify signal is emitted for each property modified while the object is frozen.
getData void* getData(string key): Gets a named field from the objects table of associations (see gobject.object.ObjectG.setData).
getProperty void getProperty(string propertyName, gobject.value.Value value): Gets a property of an object.
getQdata void* getQdata(glib.types.Quark quark): This function gets back user data pointers stored via gobject.object.ObjectG.setQdata.
getv void getv(string[] names, gobject.value.Value[] values): Gets n_properties properties for an object. Obtained properties will be set to values. All properties must be valid. Warnings will be emitted and undefined behaviour may result if invalid properties are passed in.
isFloating bool isFloating(): Checks whether object has a floating[floating-ref] reference.
notify void notify(string propertyName): Emits a "notify" signal for the property property_name on object.
notifyByPspec void notifyByPspec(gobject.param_spec.ParamSpec pspec): Emits a "notify" signal for the property specified by pspec on object.
refSink gobject.object.ObjectG refSink(): Increase the reference count of object, and possibly remove the floating[floating-ref] reference, if object has a floating reference.
runDispose void runDispose(): Releases all references to other objects. This can be used to break reference cycles.
setData void setData(string key, void* data): Each object carries around a table of associations from strings to pointers. This function lets you set an association.
setProperty void setProperty(string propertyName, gobject.value.Value value): Sets a property on an object.
stealData void* stealData(string key): Remove a specified datum from the object's data associations, without invoking the association's destroy handler.
stealQdata void* stealQdata(glib.types.Quark quark): This function gets back user data pointers stored via gobject.object.ObjectG.setQdata and removes the data from object without invoking its destroy() function (if any was set). Usually, calling this function is only required to update user data pointers with a destroy notifier, for example:
thawNotify void thawNotify(): Reverts the effect of a previous call to gobject.object.ObjectG.freezeNotify. The freeze count is decreased on object and when it reaches zero, queued "notify" signals are emitted.
watchClosure void watchClosure(gobject.closure.Closure closure): This function essentially limits the life time of the closure to the life time of the object. That is, when the object is finalized, the closure is invalidated by calling gobject.closure.Closure.invalidate on it, in order to prevent invocations of the closure with a finalized (nonexisting) object. Also, gobject.object.ObjectG.ref_ and gobject.object.ObjectG.unref are added as marshal guards to the closure, to ensure that an extra reference count is held on object during invocation of the closure. Usually, this function will be called on closures that use this object as closure data.
connectNotify ulong connectNotify(string detail, T callback, Flag!"After" after): Connect to Notify signal.

gsk glshader classes

GLShader