[core] Split layer type specific code in mbgl::Programs

Progams code for a certain layer type is encapsulted within
a dedicated `<layer type>Programs` class, inherited from
the generic base `LayerTypePrograms` class.

`mbgl::Programs::get<layer type>Programs()` lazily initializes the
layer type-specific programs code using pointer to the base class,
which allows LTO to remove this code from binaries (if the corresponding
`get<layer type>Programs()` method can never be invoked).

1 files changed, 9 insertions, 0 deletions

diff --git a/src/mbgl/programs/background_program.hpp b/src/mbgl/programs/background_program.hpp
index 667db7792b..6f9ab2a200 100644
--- a/src/mbgl/programs/background_program.hpp
+++ b/src/mbgl/programs/background_program.hpp
@@ -80,4 +80,13 @@ public:
 using BackgroundLayoutVertex = BackgroundProgram::LayoutVertex;
 using BackgroundAttributes = BackgroundProgram::Attributes;
 
+class BackgroundLayerPrograms final : public LayerTypePrograms  {
+public:
+    BackgroundLayerPrograms(gl::Context& context, const ProgramParameters& programParameters)
+        : background(context, programParameters),
+          backgroundPattern(context, programParameters) {}
+    BackgroundProgram background;
+    BackgroundPatternProgram backgroundPattern;
+};
+
 } // namespace mbgl