[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, 22 insertions, 0 deletions

diff --git a/src/mbgl/gl/primitives.hpp b/src/mbgl/gl/primitives.hpp
new file mode 100644
index 0000000000..fe6b1b2e5b
--- /dev/null
+++ b/src/mbgl/gl/primitives.hpp
@@ -0,0 +1,22 @@
+#pragma once
+
+namespace mbgl {
+namespace gl {
+
+class Point {
+public:
+    static constexpr std::size_t vertexCount = 1;
+};
+
+class Line {
+public:
+    static constexpr std::size_t vertexCount = 2;
+};
+
+class Triangle {
+public:
+    static constexpr std::size_t vertexCount = 3;
+};
+
+} // namespace gl
+} // namespace mbgl