Add padding to normal attribute in Compatibility renderer to match the RD renderers

drivers/gles3/storage/mesh_storage.cpp

@@ -217,8 +217,23 @@ void MeshStorage::mesh_add_surface(RID p_mesh, const RS::SurfaceData &p_surface)
 	if (new_surface.vertex_data.size()) {
 		glGenBuffers(1, &s->vertex_buffer);
 		glBindBuffer(GL_ARRAY_BUFFER, s->vertex_buffer);
-		GLES3::Utilities::get_singleton()->buffer_allocate_data(GL_ARRAY_BUFFER, s->vertex_buffer, new_surface.vertex_data.size(), new_surface.vertex_data.ptr(), (s->format & RS::ARRAY_FLAG_USE_DYNAMIC_UPDATE) ? GL_DYNAMIC_DRAW : GL_STATIC_DRAW, "Mesh vertex buffer");
-		s->vertex_buffer_size = new_surface.vertex_data.size();
+		// If we have an uncompressed surface that contains normals, but not tangents, we need to differentiate the array
+		// from a compressed array in the shader. To do so, we allow the the normal to read 4 components out of the buffer
+		// But only give it 2 components per normal. So essentially, each vertex reads the next normal in normal.zw.
+		// This allows us to avoid adding a shader permutation, and avoid passing dummy tangents. Since the stride is kept small
+		// this should still be a net win for bandwidth.
+		// If we do this, then the last normal will read past the end of the array. So we need to pad the array with dummy data.
+		if (!(new_surface.format & RS::ARRAY_FLAG_COMPRESS_ATTRIBUTES) && (new_surface.format & RS::ARRAY_FORMAT_NORMAL) && !(new_surface.format & RS::ARRAY_FORMAT_TANGENT)) {
+			// Unfortunately, we need to copy the buffer, which is fine as doing a resize triggers a CoW anyway.
+			Vector<uint8_t> new_vertex_data;
+			new_vertex_data.resize_zeroed(new_surface.vertex_data.size() + sizeof(uint16_t) * 2);
+			memcpy(new_vertex_data.ptrw(), new_surface.vertex_data.ptr(), new_surface.vertex_data.size());
+			GLES3::Utilities::get_singleton()->buffer_allocate_data(GL_ARRAY_BUFFER, s->vertex_buffer, new_vertex_data.size(), new_vertex_data.ptr(), (s->format & RS::ARRAY_FLAG_USE_DYNAMIC_UPDATE) ? GL_DYNAMIC_DRAW : GL_STATIC_DRAW, "Mesh vertex buffer");
+			s->vertex_buffer_size = new_vertex_data.size();
+		} else {
+			GLES3::Utilities::get_singleton()->buffer_allocate_data(GL_ARRAY_BUFFER, s->vertex_buffer, new_surface.vertex_data.size(), new_surface.vertex_data.ptr(), (s->format & RS::ARRAY_FLAG_USE_DYNAMIC_UPDATE) ? GL_DYNAMIC_DRAW : GL_STATIC_DRAW, "Mesh vertex buffer");
+			s->vertex_buffer_size = new_surface.vertex_data.size();
+		}
 	}
 
 	if (new_surface.attribute_data.size()) {
@@ -461,6 +476,11 @@ RS::SurfaceData MeshStorage::mesh_get_surface(RID p_mesh, int p_surface) const {
 	sd.format = s.format;
 	if (s.vertex_buffer != 0) {
 		sd.vertex_data = Utilities::buffer_get_data(GL_ARRAY_BUFFER, s.vertex_buffer, s.vertex_buffer_size);
+
+		// When using an uncompressed buffer with normals, but without tangents, we have to trim the padding.
+		if (!(s.format & RS::ARRAY_FLAG_COMPRESS_ATTRIBUTES) && (s.format & RS::ARRAY_FORMAT_NORMAL) && !(s.format & RS::ARRAY_FORMAT_TANGENT)) {
+			sd.vertex_data.resize(sd.vertex_data.size() - sizeof(uint16_t) * 2);
+		}
 	}
 
 	if (s.attribute_buffer != 0) {

servers/rendering/renderer_rd/storage_rd/mesh_storage.cpp

@@ -591,7 +591,6 @@ RS::SurfaceData MeshStorage::mesh_get_surface(RID p_mesh, int p_surface) const {
 		sd.vertex_data = RD::get_singleton()->buffer_get_data(s.vertex_buffer);
 		// When using an uncompressed buffer with normals, but without tangents, we have to trim the padding.
 		if (!(s.format & RS::ARRAY_FLAG_COMPRESS_ATTRIBUTES) && (s.format & RS::ARRAY_FORMAT_NORMAL) && !(s.format & RS::ARRAY_FORMAT_TANGENT)) {
-			Vector<uint8_t> new_vertex_data;
 			sd.vertex_data.resize(sd.vertex_data.size() - sizeof(uint16_t) * 2);
 		}
 	}