From 0bbc6b814cbec44be7026a0bac83d56e4d71a287 Mon Sep 17 00:00:00 2001
From: John Firebaugh <john.firebaugh@gmail.com>
Date: Wed, 8 Feb 2017 15:57:58 -0800
Subject: [core] Restore support for GL implementations without VAO extension

---
 src/mbgl/gl/context.cpp               |  14 +++++++++-----
 src/mbgl/gl/context.hpp               |   4 ++++
 src/mbgl/gl/segment.hpp               |  15 ++++++++++-----
 test/fixtures/map/no_vao/expected.png | Bin 0 -> 9832 bytes
 test/map/map.test.cpp                 |  19 +++++++++++++++++++
 5 files changed, 42 insertions(+), 10 deletions(-)
 create mode 100644 test/fixtures/map/no_vao/expected.png

diff --git a/src/mbgl/gl/context.cpp b/src/mbgl/gl/context.cpp
index a74e941bc6..5726eca5dc 100644
--- a/src/mbgl/gl/context.cpp
+++ b/src/mbgl/gl/context.cpp
@@ -123,12 +123,16 @@ UniqueTexture Context::createTexture() {
 }
 
 UniqueVertexArray Context::createVertexArray() {
-    if (!gl::GenVertexArrays) {
-        throw std::runtime_error("GL_ARB_vertex_array_object extension is required");
-    }
-
     VertexArrayID id = 0;
-    MBGL_CHECK_ERROR(gl::GenVertexArrays(1, &id));
+    if (gl::GenVertexArrays && !disableVAOExtension) {
+        MBGL_CHECK_ERROR(gl::GenVertexArrays(1, &id));
+    } else {
+        static bool reported = false;
+        if (!reported) {
+            Log::Warning(Event::OpenGL, "Not using Vertex Array Objects");
+            reported = true;
+        }
+    }
     return UniqueVertexArray(std::move(id), { this });
 }
 
diff --git a/src/mbgl/gl/context.hpp b/src/mbgl/gl/context.hpp
index 636dfc9eac..d1be794240 100644
--- a/src/mbgl/gl/context.hpp
+++ b/src/mbgl/gl/context.hpp
@@ -222,6 +222,10 @@ private:
     std::vector<VertexArrayID> abandonedVertexArrays;
     std::vector<FramebufferID> abandonedFramebuffers;
     std::vector<RenderbufferID> abandonedRenderbuffers;
+
+public:
+    // For testing
+    bool disableVAOExtension = false;
 };
 
 } // namespace gl
diff --git a/src/mbgl/gl/segment.hpp b/src/mbgl/gl/segment.hpp
index bb9f2f1ee8..7ce90e53a6 100644
--- a/src/mbgl/gl/segment.hpp
+++ b/src/mbgl/gl/segment.hpp
@@ -37,12 +37,17 @@ public:
             context.vertexBuffer.setDirty();
         }
 
-        context.vertexArrayObject = *vao;
-
-        if (indexBuffer != indexBuffer_) {
-            indexBuffer = indexBuffer_;
-            context.elementBuffer.setDirty();
+        if (*vao) {
+            context.vertexArrayObject = *vao;
+            if (indexBuffer != indexBuffer_) {
+                indexBuffer = indexBuffer_;
+                context.elementBuffer.setDirty();
+                context.elementBuffer = indexBuffer_;
+            }
+        } else {
+            // No VAO support. Force attributes to be rebound.
             context.elementBuffer = indexBuffer_;
+            variableBindings = {};
         }
 
         Attributes::bind(context,
diff --git a/test/fixtures/map/no_vao/expected.png b/test/fixtures/map/no_vao/expected.png
new file mode 100644
index 0000000000..d5b7c42762
Binary files /dev/null and b/test/fixtures/map/no_vao/expected.png differ
diff --git a/test/map/map.test.cpp b/test/map/map.test.cpp
index fd3bfe58d7..aec181e058 100644
--- a/test/map/map.test.cpp
+++ b/test/map/map.test.cpp
@@ -6,6 +6,7 @@
 #include <mbgl/map/map.hpp>
 #include <mbgl/gl/headless_backend.hpp>
 #include <mbgl/gl/offscreen_view.hpp>
+#include <mbgl/gl/context.hpp>
 #include <mbgl/util/default_thread_pool.hpp>
 #include <mbgl/sprite/sprite_image.hpp>
 #include <mbgl/storage/network_status.hpp>
@@ -305,6 +306,24 @@ TEST(Map, AddLayer) {
     test::checkImage("test/fixtures/map/add_layer", test::render(map, test.view));
 }
 
+TEST(Map, WithoutVAOExtension) {
+    MapTest test;
+
+    test.backend.getContext().disableVAOExtension = true;
+
+#ifdef MBGL_ASSET_ZIP
+    // Regenerate with `cd test/fixtures/api/ && zip -r assets.zip assets/`
+    DefaultFileSource fileSource(":memory:", "test/fixtures/api/assets.zip");
+#else
+    DefaultFileSource fileSource(":memory:", "test/fixtures/api/assets");
+#endif
+
+    Map map(test.backend, test.view.size, 1, fileSource, test.threadPool, MapMode::Still);
+    map.setStyleJSON(util::read_file("test/fixtures/api/water.json"));
+
+    test::checkImage("test/fixtures/map/no_vao", test::render(map, test.view), 0.002);
+}
+
 TEST(Map, RemoveLayer) {
     MapTest test;
 
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