### Enumeration

# Cogl SnippetHook

#### Declaration

    enum Cogl.SnippetHook

#### Description [src]

`CoglSnippetHook` is used to specify a location within a `CoglPipeline` where the code of the snippet should be used when it is attached to a pipeline.

- `COGL_SNIPPET_HOOK_VERTEX_GLOBALS`

Adds a shader snippet at the beginning of the global section of the shader for the vertex processing. Any declarations here can be shared with all other snippets that are attached to a vertex hook. Only the ‘declarations’ string is used and the other strings are ignored.

- `COGL_SNIPPET_HOOK_FRAGMENT_GLOBALS`

Adds a shader snippet at the beginning of the global section of the shader for the fragment processing. Any declarations here can be shared with all other snippets that are attached to a fragment hook. Only the ‘declarations’ string is used and the other strings are ignored.

- `COGL_SNIPPET_HOOK_VERTEX`

Adds a shader snippet that will hook on to the vertex processing stage of the pipeline. This gives a chance for the application to modify the vertex attributes generated by the shader. Typically the snippet will modify cogl_color_out or cogl_position_out builtins.

The ‘declarations’ string in `snippet` will be inserted in the global scope of the shader. Use this to declare any uniforms, attributes or functions that the snippet requires.

The ‘pre’ string in `snippet` will be inserted at the top of the `main()` function before any vertex processing is done.

The ‘replace’ string in `snippet` will be used instead of the generated vertex processing if it is present. This can be used if the application wants to provide a complete vertex shader and doesn’t need the generated output from Cogl.

The ‘post’ string in `snippet` will be inserted after all of the standard vertex processing is done. This can be used to modify the outputs.

- `COGL_SNIPPET_HOOK_VERTEX_TRANSFORM`

Adds a shader snippet that will hook on to the vertex transform stage. Typically the snippet will use the cogl_modelview_matrix, cogl_projection_matrix and cogl_modelview_projection_matrix matrices and the cogl_position_in attribute. The hook must write to cogl_position_out. The default processing for this hook will multiply cogl_position_in by the combined modelview-projection matrix and store it on cogl_position_out.

The ‘declarations’ string in `snippet` will be inserted in the global scope of the shader. Use this to declare any uniforms, attributes or functions that the snippet requires.

The ‘pre’ string in `snippet` will be inserted at the top of the `main()` function before the vertex transform is done.

The ‘replace’ string in `snippet` will be used instead of the generated vertex transform if it is present.

The ‘post’ string in `snippet` will be inserted after all of the standard vertex transformation is done. This can be used to modify the cogl_position_out in addition to the default processing.

- `COGL_SNIPPET_HOOK_POINT_SIZE`

Adds a shader snippet that will hook on to the point size calculation step within the vertex shader stage. The snippet should write to the builtin cogl_point_size_out with the new point size. The snippet can either read cogl_point_size_in directly and write a new value or first read an existing value in cogl_point_size_out that would be set by a previous snippet. Note that this hook is only used if `cogl_pipeline_set_per_vertex_point_size()` is enabled on the pipeline.

The ‘declarations’ string in `snippet` will be inserted in the global scope of the shader. Use this to declare any uniforms, attributes or functions that the snippet requires.

The ‘pre’ string in `snippet` will be inserted just before calculating the point size.

The ‘replace’ string in `snippet` will be used instead of the generated point size calculation if it is present.

The ‘post’ string in `snippet` will be inserted after the standard point size calculation is done. This can be used to modify cogl_point_size_out in addition to the default processing.

- `COGL_SNIPPET_HOOK_FRAGMENT`

Adds a shader snippet that will hook on to the fragment processing stage of the pipeline. This gives a chance for the application to modify the fragment color generated by the shader. Typically the snippet will modify cogl_color_out.

The ‘declarations’ string in `snippet` will be inserted in the global scope of the shader. Use this to declare any uniforms, attributes or functions that the snippet requires.

The ‘pre’ string in `snippet` will be inserted at the top of the `main()` function before any fragment processing is done.

The ‘replace’ string in `snippet` will be used instead of the generated fragment processing if it is present. This can be used if the application wants to provide a complete fragment shader and doesn’t need the generated output from Cogl.

The ‘post’ string in `snippet` will be inserted after all of the standard fragment processing is done. At this point the generated value for the rest of the pipeline state will already be in cogl_color_out so the application can modify the result by altering this variable.

- `COGL_SNIPPET_HOOK_TEXTURE_COORD_TRANSFORM`

Adds a shader snippet that will hook on to the texture coordinate transformation of a particular layer. This can be used to replace the processing for a layer or to modify the results.

Within the snippet code for this hook there are two extra variables. The first is a mat4 called cogl_matrix which represents the user matrix for this layer. The second is called cogl_tex_coord and represents the incoming and outgoing texture coordinate. On entry to the hook, cogl_tex_coord contains the value of the corresponding texture coordinate attribute for this layer. The hook is expected to modify this variable. The output will be passed as a varying to the fragment processing stage. The default code will just multiply cogl_matrix by cogl_tex_coord and store the result in cogl_tex_coord.

The ‘declarations’ string in `snippet` will be inserted in the global scope of the shader. Use this to declare any uniforms, attributes or functions that the snippet requires.

The ‘pre’ string in `snippet` will be inserted just before the fragment processing for this layer. At this point cogl_tex_coord still contains the value of the texture coordinate attribute. If a ‘replace’ string is given then this will be used instead of the default fragment processing for this layer. The snippet can modify cogl_tex_coord or leave it as is to apply no transformation.

The ‘post’ string in `snippet` will be inserted just after the transformation. At this point cogl_tex_coord will contain the results of the transformation but it can be further modified by the snippet.

- `COGL_SNIPPET_HOOK_LAYER_FRAGMENT`

Adds a shader snippet that will hook on to the fragment processing of a particular layer. This can be used to replace the processing for a layer or to modify the results.

Within the snippet code for this hook there is an extra vec4 variable called ‘cogl_layer’. This contains the resulting color that will be used for the layer. This can be modified in the ‘post’ section or it the default processing can be replaced entirely using the ‘replace’ section.

The ‘declarations’ string in `snippet` will be inserted in the global scope of the shader. Use this to declare any uniforms, attributes or functions that the snippet requires.

The ‘pre’ string in `snippet` will be inserted just before the fragment processing for this layer.

If a ‘replace’ string is given then this will be used instead of the default fragment processing for this layer. The snippet must write to the ‘cogl_layer’ variable in that case.

The ‘post’ string in `snippet` will be inserted just after the fragment processing for the layer. The results can be modified by changing the value of the ‘cogl_layer’ variable.

- `COGL_SNIPPET_HOOK_TEXTURE_LOOKUP`

Adds a shader snippet that will hook on to the texture lookup part of a given layer. This gives a chance for the application to modify the coordinates that will be used for the texture lookup or to alter the returned texel.

Within the snippet code for this hook there are three extra variables available. ‘cogl_sampler’ is a sampler object representing the sampler for the layer where the snippet is attached. ‘cogl_tex_coord’ is a vec4 which contains the texture coordinates that will be used for the texture lookup. This can be modified. ‘cogl_texel’ will contain the result of the texture lookup. This can also be modified.

The ‘declarations’ string in `snippet` will be inserted in the global scope of the shader. Use this to declare any uniforms, attributes or functions that the snippet requires.

The ‘pre’ string in `snippet` will be inserted at the top of the `main()` function before any fragment processing is done. This is a good place to modify the cogl_tex_coord variable.

If a ‘replace’ string is given then this will be used instead of a the default texture lookup. The snippet would typically use its own sampler in this case.

The ‘post’ string in `snippet` will be inserted after texture lookup has been performed. Here the snippet can modify the cogl_texel variable to alter the returned texel.

#### Members

`COGL_SNIPPET_HOOK_VERTEX`

  A hook for the entire vertex processing stage of the pipeline.

  - Value: `0`
  - Available since: 14
`COGL_SNIPPET_HOOK_VERTEX_TRANSFORM`

  A hook for the vertex transformation.

  - Value: `1`
  - Available since: 14
`COGL_SNIPPET_HOOK_VERTEX_GLOBALS`

  A hook for declaring global data that can be shared with all other snippets that are on a vertex hook.

  - Value: `2`
  - Available since: 14
`COGL_SNIPPET_HOOK_POINT_SIZE`

  A hook for manipulating the point size of a vertex. This is only used if `cogl_pipeline_set_per_vertex_point_size()` is enabled on the pipeline.

  - Value: `3`
  - Available since: 14
`COGL_SNIPPET_HOOK_FRAGMENT`

  A hook for the entire fragment processing stage of the pipeline.

  - Value: `2048`
  - Available since: 14
`COGL_SNIPPET_HOOK_FRAGMENT_GLOBALS`

  A hook for declaring global data wthat can be shared with all other snippets that are on a fragment hook.

  - Value: `2049`
  - Available since: 14
`COGL_SNIPPET_HOOK_TEXTURE_COORD_TRANSFORM`

  A hook for applying the layer matrix to a texture coordinate for a layer.

  - Value: `4096`
  - Available since: 14
`COGL_SNIPPET_HOOK_LAYER_FRAGMENT`

  A hook for the fragment processing of a particular layer.

  - Value: `6144`
  - Available since: 14
`COGL_SNIPPET_HOOK_TEXTURE_LOOKUP`

  A hook for the texture lookup stage of a given layer in a pipeline.

  - Value: `6145`
  - Available since: 14