[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.

9 files changed, 43 insertions, 3 deletions

diff --git a/src/mbgl/programs/circle_program.hpp b/src/mbgl/programs/circle_program.hpp
index 690608a438..75c030b1c8 100644
--- a/src/mbgl/programs/circle_program.hpp
+++ b/src/mbgl/programs/circle_program.hpp
@@ -16,6 +16,7 @@ MBGL_DEFINE_UNIFORM_SCALAR(float, u_devicepixelratio);
 
 class CircleProgram : public Program<
     shaders::circle,
+    gl::Triangle,
     gl::Attributes<
         attributes::a_pos>,
     gl::Uniforms<
diff --git a/src/mbgl/programs/collision_box_program.hpp b/src/mbgl/programs/collision_box_program.hpp
index 66b1284621..5eda3fefb0 100644
--- a/src/mbgl/programs/collision_box_program.hpp
+++ b/src/mbgl/programs/collision_box_program.hpp
@@ -17,6 +17,7 @@ MBGL_DEFINE_UNIFORM_SCALAR(float, u_maxzoom);
 
 class CollisionBoxProgram : public Program<
     shaders::collision_box,
+    gl::Line,
     gl::Attributes<
         attributes::a_pos,
         attributes::a_extrude,
diff --git a/src/mbgl/programs/debug_program.hpp b/src/mbgl/programs/debug_program.hpp
new file mode 100644
index 0000000000..3596dc1f7e
--- /dev/null
+++ b/src/mbgl/programs/debug_program.hpp
@@ -0,0 +1,23 @@
+#pragma once
+
+#include <mbgl/programs/program.hpp>
+#include <mbgl/programs/attributes.hpp>
+#include <mbgl/programs/uniforms.hpp>
+#include <mbgl/shader/debug.hpp>
+
+namespace mbgl {
+
+class DebugProgram : public Program<
+    shaders::debug,
+    gl::Line,
+    gl::Attributes<
+        attributes::a_pos>,
+    gl::Uniforms<
+        uniforms::u_matrix,
+        uniforms::u_color>>
+{
+public:
+    using Program::Program;
+};
+
+} // namespace mbgl
diff --git a/src/mbgl/programs/fill_program.hpp b/src/mbgl/programs/fill_program.hpp
index 3f738527c8..d885215c59 100644
--- a/src/mbgl/programs/fill_program.hpp
+++ b/src/mbgl/programs/fill_program.hpp
@@ -86,6 +86,7 @@ struct FillPatternUniforms : gl::Uniforms<
 
 class FillProgram : public Program<
     shaders::fill,
+    gl::Triangle,
     FillAttributes,
     FillUniforms>
 {
@@ -94,6 +95,7 @@ class FillProgram : public Program<
 
 class FillPatternProgram : public Program<
     shaders::fill_pattern,
+    gl::Triangle,
     FillAttributes,
     FillPatternUniforms>
 {
@@ -102,6 +104,7 @@ class FillPatternProgram : public Program<
 
 class FillOutlineProgram : public Program<
     shaders::fill_outline,
+    gl::Line,
     FillAttributes,
     FillUniforms>
 {
@@ -110,6 +113,7 @@ class FillOutlineProgram : public Program<
 
 class FillOutlinePatternProgram : public Program<
     shaders::fill_outline_pattern,
+    gl::Line,
     FillAttributes,
     FillPatternUniforms>
 {
diff --git a/src/mbgl/programs/line_program.hpp b/src/mbgl/programs/line_program.hpp
index 960438f4cd..07ae35b8ed 100644
--- a/src/mbgl/programs/line_program.hpp
+++ b/src/mbgl/programs/line_program.hpp
@@ -88,6 +88,7 @@ using LineVertex = LineAttributes::Vertex;
 
 class LineProgram : public Program<
     shaders::line,
+    gl::Triangle,
     LineAttributes,
     gl::Uniforms<
         uniforms::u_matrix,
@@ -113,6 +114,7 @@ public:
 
 class LinePatternProgram : public Program<
     shaders::line_pattern,
+    gl::Triangle,
     LineAttributes,
     gl::Uniforms<
         uniforms::u_matrix,
@@ -147,6 +149,7 @@ public:
 
 class LineSDFProgram : public Program<
     shaders::line_sdf,
+    gl::Triangle,
     LineAttributes,
     gl::Uniforms<
         uniforms::u_matrix,
diff --git a/src/mbgl/programs/program.hpp b/src/mbgl/programs/program.hpp
index 9f154b051a..fa41d43e5c 100644
--- a/src/mbgl/programs/program.hpp
+++ b/src/mbgl/programs/program.hpp
@@ -11,11 +11,13 @@ enum class ProgramDefines : bool {
     Overdraw = true,
 };
 
-template <class Shaders, class As, class Us>
-class Program : public gl::Program<As, Us> {
+template <class Shaders, class Primitive, class Attributes, class Uniforms>
+class Program : public gl::Program<Primitive, Attributes, Uniforms> {
 public:
+    using ParentType = gl::Program<Primitive, Attributes, Uniforms>;
+
     Program(gl::Context& context, ProgramDefines defines)
-        : gl::Program<As, Us>(context, Shaders::vertexSource, fragmentSource(defines))
+        : ParentType(context, Shaders::vertexSource, fragmentSource(defines))
         {}
 
     static std::string fragmentSource(ProgramDefines defines) {
diff --git a/src/mbgl/programs/programs.hpp b/src/mbgl/programs/programs.hpp
index aebafaec62..53ed26e969 100644
--- a/src/mbgl/programs/programs.hpp
+++ b/src/mbgl/programs/programs.hpp
@@ -5,6 +5,7 @@
 #include <mbgl/programs/line_program.hpp>
 #include <mbgl/programs/raster_program.hpp>
 #include <mbgl/programs/symbol_program.hpp>
+#include <mbgl/programs/debug_program.hpp>
 #include <mbgl/programs/collision_box_program.hpp>
 
 namespace mbgl {
@@ -24,6 +25,7 @@ public:
           symbolIcon(context, defines),
           symbolIconSDF(context, defines),
           symbolGlyph(context, defines),
+          debug(context, ProgramDefines::None),
           collisionBox(context, ProgramDefines::None) {
     }
 
@@ -40,6 +42,7 @@ public:
     SymbolSDFProgram symbolIconSDF;
     SymbolSDFProgram symbolGlyph;
 
+    DebugProgram debug;
     CollisionBoxProgram collisionBox;
 };
 
diff --git a/src/mbgl/programs/raster_program.hpp b/src/mbgl/programs/raster_program.hpp
index 1e9a0cdb6a..1bab2d5765 100644
--- a/src/mbgl/programs/raster_program.hpp
+++ b/src/mbgl/programs/raster_program.hpp
@@ -25,6 +25,7 @@ MBGL_DEFINE_UNIFORM_VECTOR(float, 2, u_tl_parent);
 
 class RasterProgram : public Program<
     shaders::raster,
+    gl::Triangle,
     gl::Attributes<
         attributes::a_pos,
         attributes::a_texture_pos>,
diff --git a/src/mbgl/programs/symbol_program.hpp b/src/mbgl/programs/symbol_program.hpp
index eb8c56b326..be987551c0 100644
--- a/src/mbgl/programs/symbol_program.hpp
+++ b/src/mbgl/programs/symbol_program.hpp
@@ -72,6 +72,7 @@ using SymbolVertex = SymbolAttributes::Vertex;
 
 class SymbolIconProgram : public Program<
     shaders::symbol_icon,
+    gl::Triangle,
     SymbolAttributes,
     gl::Uniforms<
         uniforms::u_matrix,
@@ -95,6 +96,7 @@ public:
 
 class SymbolSDFProgram : public Program<
     shaders::symbol_sdf,
+    gl::Triangle,
     SymbolAttributes,
     gl::Uniforms<
         uniforms::u_matrix,