[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, 2 insertions, 2 deletions

diff --git a/src/mbgl/gl/context.cpp b/src/mbgl/gl/context.cpp
index b12c77c1a1..c4485ad0fd 100644
--- a/src/mbgl/gl/context.cpp
+++ b/src/mbgl/gl/context.cpp
@@ -533,9 +533,9 @@ void Context::draw(const Drawable& drawable) {
         if (drawable.indexBuffer) {
             MBGL_CHECK_ERROR(glDrawElements(
                 static_cast<GLenum>(primitiveType),
-                static_cast<GLsizei>(drawable.primitiveSize / sizeof(uint16_t) * segment.primitiveLength),
+                static_cast<GLsizei>(segment.indexLength),
                 GL_UNSIGNED_SHORT,
-                reinterpret_cast<GLvoid*>(drawable.primitiveSize * segment.primitiveOffset)));
+                reinterpret_cast<GLvoid*>(sizeof(uint16_t) * segment.indexOffset)));
         } else {
             MBGL_CHECK_ERROR(glDrawArrays(
                 static_cast<GLenum>(primitiveType),