Package ch.bailu.gtk.gsk

Class GLShader

java.lang.Object
ch.bailu.gtk.type.Type
ch.bailu.gtk.type.Pointer
ch.bailu.gtk.gobject.Object
ch.bailu.gtk.gsk.GLShader
All Implemented Interfaces:
PointerInterface
public class GLShader extends Object
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 [class@Gsk.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:

```glsl
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:

```glsl
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:

```glsl
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 [method@Gsk.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

```glsl
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;
}
```

https://docs.gtk.org/gsk4/class.GLShader.html

  • Constructor Details

  • Method Details

    • getClassHandler

      public static ClassHandler getClassHandler()

    • newFromBytesGLShader

      public static GLShader newFromBytesGLShader(@Nonnull Bytes 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`

    • newFromResourceGLShader

      public static GLShader newFromResourceGLShader(@Nonnull Str 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`

    • newFromResourceGLShader

      public static GLShader newFromResourceGLShader(String 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`

    • compile

      public boolean compile(@Nonnull Renderer renderer) throws AllocationError
      Tries to compile the @shader for the given @renderer.

      If there is a problem, this function returns %FALSE and reports
      an error. 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:
      renderer - a `GskRenderer`
      Returns:
      %TRUE on success, %FALSE if an error occurred
      Throws:
      AllocationError

    • findUniformByName

      public int findUniformByName(@Nonnull Str name)
      Looks for a uniform by the name @name, and returns the index
      of the uniform, or -1 if it was not found.
      Parameters:
      name - uniform name
      Returns:
      The index of the uniform, or -1

    • findUniformByName

      public 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.
      Parameters:
      name - uniform name
      Returns:
      The index of the uniform, or -1

    • formatArgs

      public Bytes formatArgs(Object... _elipse)
      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:
      _elipse - 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 [ctor@Gsk.GLShaderNode.new].

    • getArgBool

      public boolean getArgBool(@Nonnull Bytes args, int idx)
      Gets the value of the uniform @idx in the @args block.

      The uniform must be of bool type.
      Parameters:
      args - uniform arguments
      idx - index of the uniform
      Returns:
      The value

    • getArgFloat

      public float getArgFloat(@Nonnull Bytes args, int idx)
      Gets the value of the uniform @idx in the @args block.

      The uniform must be of float type.
      Parameters:
      args - uniform arguments
      idx - index of the uniform
      Returns:
      The value

    • getArgInt

      public int getArgInt(@Nonnull Bytes args, int idx)
      Gets the value of the uniform @idx in the @args block.

      The uniform must be of int type.
      Parameters:
      args - uniform arguments
      idx - index of the uniform
      Returns:
      The value

    • getArgUint

      public int getArgUint(@Nonnull Bytes args, int idx)
      Gets the value of the uniform @idx in the @args block.

      The uniform must be of uint type.
      Parameters:
      args - uniform arguments
      idx - index of the uniform
      Returns:
      The value

    • getArgVec2

      public void getArgVec2(@Nonnull Bytes args, int idx, @Nonnull Vec2 out_value)
      Gets the value of the uniform @idx in the @args block.

      The uniform must be of vec2 type.
      Parameters:
      args - uniform arguments
      idx - index of the uniform
      out_value - location to store the uniform value in

    • getArgVec3

      public void getArgVec3(@Nonnull Bytes args, int idx, @Nonnull Vec3 out_value)
      Gets the value of the uniform @idx in the @args block.

      The uniform must be of vec3 type.
      Parameters:
      args - uniform arguments
      idx - index of the uniform
      out_value - location to store the uniform value in

    • getArgVec4

      public void getArgVec4(@Nonnull Bytes args, int idx, @Nonnull Vec4 out_value)
      Gets the value of the uniform @idx in the @args block.

      The uniform must be of vec4 type.
      Parameters:
      args - uniform arguments
      idx - index of the uniform
      out_value - location to store set the uniform value in

    • getArgsSize

      public long getArgsSize()
      Get the size of the data block used to specify arguments for this shader.
      Returns:
      The size of the data block

    • getNTextures

      public int getNTextures()
      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.
      Returns:
      The number of texture inputs required by @shader

    • getNUniforms

      public int getNUniforms()
      Get the number of declared uniforms for this shader.
      Returns:
      The number of declared uniforms

    • getResource

      public Str getResource()
      Gets the resource path for the GLSL sourcecode being used
      to render this shader.
      Returns:
      The resource path for the shader

    • getSource

      public Bytes getSource()
      Gets the GLSL sourcecode being used to render this shader.
      Returns:
      The source code for the shader

    • getUniformName

      public Str getUniformName(int idx)
      Get the name of the declared uniform for this shader at index @idx.
      Parameters:
      idx - index of the uniform
      Returns:
      The name of the declared uniform

    • getUniformOffset

      public int getUniformOffset(int idx)
      Get the offset into the data block where data for this uniforms is stored.
      Parameters:
      idx - index of the uniform
      Returns:
      The data offset

    • getUniformType

      public int getUniformType(int idx)
      Get the type of the declared uniform for this shader at index @idx.
      Parameters:
      idx - index of the uniform
      Returns:
      The type of the declared uniform

    • getTypeID

      public static long getTypeID()

    • getParentTypeID

      public static long getParentTypeID()

    • getTypeSize

      public static TypeSystem.TypeSize getTypeSize()

    • getParentTypeSize

      public static TypeSystem.TypeSize getParentTypeSize()

    • getInstanceSize

      public static int getInstanceSize()