Drop enable_vbo setting

Consistently applying this setting requires some code work,
because Irrlicht does not provide a global toggle.
At the same time I don't see any reason for someone to disable this.

builtin/settingtypes.txt

@@ -1816,10 +1816,6 @@ video_driver (Video driver) enum  ,opengl,opengl3,ogles1,ogles2
 #    Use this to limit the performance impact of transparency depth sorting
 transparency_sorting_distance (Transparency Sorting Distance) int 16 0 128
 
-#    Enable vertex buffer objects.
-#    This should greatly improve graphics performance.
-enable_vbo (VBO) bool true
-
 #    Radius of cloud area stated in number of 64 node cloud squares.
 #    Values larger than 26 will start to produce sharp cutoffs at cloud area corners.
 cloud_radius (Cloud radius) int 12 1 62

src/client/mapblock_mesh.cpp

@@ -645,7 +645,6 @@ MapBlockMesh::MapBlockMesh(Client *client, MeshMakeData *data, v3s16 camera_offs
 	for (auto &m : m_mesh)
 		m = new scene::SMesh();
 	m_enable_shaders = data->m_use_shaders;
-	m_enable_vbo = g_settings->getBool("enable_vbo");
 
 	auto mesh_grid = client->getMeshGrid();
 	v3s16 bp = data->m_blockpos;
@@ -692,6 +691,8 @@ MapBlockMesh::MapBlockMesh(Client *client, MeshMakeData *data, v3s16 camera_offs
 	m_bounding_radius = std::sqrt(collector.m_bounding_radius_sq);
 
 	for (int layer = 0; layer < MAX_TILE_LAYERS; layer++) {
+		scene::SMesh *mesh = (scene::SMesh *)m_mesh[layer];
+
 		for(u32 i = 0; i < collector.prebuffers[layer].size(); i++)
 		{
 			PreMeshBuffer &p = collector.prebuffers[layer][i];
@@ -783,8 +784,6 @@ MapBlockMesh::MapBlockMesh(Client *client, MeshMakeData *data, v3s16 camera_offs
 				p.layer.applyMaterialOptions(material);
 			}
 
-			scene::SMesh *mesh = (scene::SMesh *)m_mesh[layer];
-
 			scene::SMeshBuffer *buf = new scene::SMeshBuffer();
 			buf->Material = material;
 			if (p.layer.isTransparent()) {
@@ -808,10 +807,9 @@ MapBlockMesh::MapBlockMesh(Client *client, MeshMakeData *data, v3s16 camera_offs
 			buf->drop();
 		}
 
-		if (m_mesh[layer]) {
+		if (mesh) {
 			// Use VBO for mesh (this just would set this for ever buffer)
-			if (m_enable_vbo)
-				m_mesh[layer]->setHardwareMappingHint(scene::EHM_STATIC);
+			mesh->setHardwareMappingHint(scene::EHM_STATIC);
 		}
 	}
 
@@ -896,15 +894,13 @@ bool MapBlockMesh::animate(bool faraway, float time, int crack,
 
 	// Day-night transition
 	if (!m_enable_shaders && (daynight_ratio != m_last_daynight_ratio)) {
-		// Force reload mesh to VBO
-		if (m_enable_vbo)
-			for (scene::IMesh *m : m_mesh)
-				m->setDirty();
 		video::SColorf day_color;
 		get_sunlight_color(&day_color, daynight_ratio);
 
 		for (auto &daynight_diff : m_daynight_diffs) {
-			scene::IMeshBuffer *buf = m_mesh[daynight_diff.first.first]->
+			auto *mesh = m_mesh[daynight_diff.first.first];
+			mesh->setDirty(scene::EBT_VERTEX); // force reload to VBO
+			scene::IMeshBuffer *buf = mesh->
 				getMeshBuffer(daynight_diff.first.second);
 			video::S3DVertex *vertices = (video::S3DVertex *)buf->getVertices();
 			for (const auto &j : daynight_diff.second)

src/client/mapblock_mesh.h

@@ -250,7 +250,6 @@ private:
 	v3f m_bounding_sphere_center;
 
 	bool m_enable_shaders;
-	bool m_enable_vbo;
 
 	// Must animate() be called before rendering?
 	bool m_has_animation;

src/defaultsettings.cpp

@@ -51,7 +51,6 @@ void set_default_settings()
 	settings->setDefault("enable_mesh_cache", "false");
 	settings->setDefault("mesh_generation_interval", "0");
 	settings->setDefault("mesh_generation_threads", "0");
-	settings->setDefault("enable_vbo", "true");
 	settings->setDefault("free_move", "false");
 	settings->setDefault("pitch_move", "false");
 	settings->setDefault("fast_move", "false");