[core] Use gl::Program to resolve some rough edges in the GL binding types

* Extract `ignore` util to separate header.
* `Segment` now tracks offset and length of indices, rather than primitives. This is more natural.
* Introduce `VertexVector` and `IndexVector` types. These types carry information about the intended draw mode (`Triangles`, `LineStrip`, etc.), and ensure that elements are always appended in a group size appropriate for that draw mode, for both indexed and unindexed rendering.
* `Program`, rather than `Drawable`, is now the unifying object for draw calls. `Program` is the best place to type check the draw call, because it is typed to carry information about the intended primitive, vertex type, attributes, and uniforms.
* Use the debug shaders for debug tile rendering, like gl-js.
* Fix the draw mode for background. It was drawing triangle strips with a triangles array. Surprised this didn’t cause issues. Now it’s type checked.

1 files changed, 21 insertions, 0 deletions

diff --git a/src/mbgl/util/ignore.hpp b/src/mbgl/util/ignore.hpp
new file mode 100644
index 0000000000..31cd092c0e
--- /dev/null
+++ b/src/mbgl/util/ignore.hpp
@@ -0,0 +1,21 @@
+#pragma once
+
+#include <initializer_list>
+
+namespace mbgl {
+
+// Accept any number of parameters of any types, and do nothing with them.
+// Useful for providing a context for parameter pack expansion where a legal
+// expansion context is not otherwise available.
+//
+// See https://github.com/mapbox/cpp/blob/master/C%2B%2B%20Structural%20Metaprogramming.md
+// for more details.
+//
+template <class... Ts> void ignore(Ts&&...) {}
+
+// std::initializer_list overload, for situations where you need sequenced
+// modifications.
+//
+template <class T> void ignore(const std::initializer_list<T>&) {}
+
+} // namespace mbgl