Add shader registry (#924)

test/map/map.test.cpp

@@ -7,6 +7,7 @@
 
 #include <mbgl/gfx/backend_scope.hpp>
 #include <mbgl/gfx/headless_frontend.hpp>
+#include <mbgl/gfx/shader_registry.hpp>
 #include <mbgl/gl/context.hpp>
 #include <mbgl/map/map_options.hpp>
 #include <mbgl/math/log2.hpp>
@@ -1576,3 +1577,23 @@ TEST(Map, VolatileSource) {
     test.runLoop.run();
     EXPECT_EQ(8, requestedTiles);
 }
+
+TEST(Map, ObserveShaderRegistration) {
+    MapTest<> test;
+
+    bool observedRegistry = false;
+    test.observer.onRegisterShadersCallback = [&observedRegistry](gfx::ShaderRegistry&) {
+        observedRegistry = true;
+    };
+
+    test.map.jumpTo(CameraOptions().withZoom(10));
+    test.map.getStyle().loadJSON(util::read_file("test/fixtures/api/empty.json"));
+    
+    test.frontend.render(test.map);
+    EXPECT_EQ(observedRegistry, true);
+    
+    // Should not see it again
+    observedRegistry = false;
+    test.frontend.render(test.map);
+    EXPECT_EQ(observedRegistry, false);
+}