GPUShader: Add support for vertex shader gl_Layer and fallback

This adds the possibility to use the `gpu_Layer` builtin to
support layered rendering without geometry shader.

The `BuiltinBits::LAYER` builtin needs to be manually added
to the `GPUShaderCreateInfo` in order to use this feature.
Note: This is only available for shaders using `GPUShaderCreateInfo`.

A geometry shader fallback is generated if the extension
`AMD_shader_explicit_vertex_parameter` is not available.

1 files changed, 8 insertions, 0 deletions

diff --git a/source/blender/gpu/opengl/gl_shader.hh b/source/blender/gpu/opengl/gl_shader.hh
index a82ab026c16..cc1c93142f8 100644
--- a/source/blender/gpu/opengl/gl_shader.hh
+++ b/source/blender/gpu/opengl/gl_shader.hh
@@ -94,6 +94,14 @@ class GLShader : public Shader {
   /** Create, compile and attach the shader stage to the shader program. */
   GLuint create_shader_stage(GLenum gl_stage, MutableSpan<const char *> sources);
 
+  /**
+   * \brief features available on newer implementation such as native barycentric coordinates
+   * and layered rendering, necessitate a geometry shader to work on older hardware.
+   */
+  std::string workaround_geometry_shader_source_create(const shader::ShaderCreateInfo &info);
+
+  bool do_geometry_shader_injection(const shader::ShaderCreateInfo *info);
+
   MEM_CXX_CLASS_ALLOC_FUNCS("GLShader");
 };