Complete Guide to the 3D Pipeline #2: Mesh Optimization
This article is for beginners looking to become 3D artists. By the time you finish reading, you will know how game engines deceive us, why to be afraid of triangulation distortion, and what the deal is with cylinders. A careful study of the text will take about 8 minutes.
This is the third part of the AAA pipeline series. Here are links to all six. Choose the one you need:
Mesh is a three-dimensional structure that defines the shape of a model. Think of it as a wireframe or skeleton. Before digging into mesh optimization, you should understand some technical details. It may be challenging, though it is noteworthy.
So, let’s go over which elements make up the mesh.
Vertex is the essential element of 3D geometry.
Edge is two vertices connected by a line.
Polygon is a geometrical figure consisting of vertices and edges. The simplest example of a polygon is a triangle.
Why does the mesh need optimization?
Look at this picture of the same model opened in different software. While it renders similarly in Maya and Unreal, some issues occurred in Marmoset.
The thing is, there are countless types of polygons in geometry, and you can create them all. However, they are abstractions used to simplify the process. Ultimately, all 3D software and game engines render models as a mesh of triangles. For example, a square will be automatically converted into two triangles after uploading to a project.
Triangulation is transforming all the polygons of a model into triangles. Due to different algorithms in various software, the process can act unpredictably and deform your model.
If there is a square on the model and all vertices lie in the same plane, there won’t be any issues. However, if one or more vertices extend beyond the plane, problems may arise. This is known as triangulation distortion, and it's a good reason to optimize the mesh and convert polygons manually.
Types of mesh
After the blocking-out stage, the mesh on your model is unorganized. Just upload a blockout in a game, and you will face triangulation problems or exceed the polygon limit. To meet all the requirements, 3D artists use three types of meshes.
Low poly models are the ones used in games. They should maintain a balance between detail and lightness, forming a silhouette of an object. All the flat elements transfer as a special texture from a High poly model. Low poly differs from game to game. On mobile phones, the model should be extremely light, with an average of 6,000 triangles. At the same time, Kratos from God of War (2018) has about 80,000 triangles.
High poly models have a high level of detail. There are no restrictions on the number of polygons as long as your computer can handle the file. In game development, High poly modeling aims to make extra surface details and transfer them to Low poly as textures.
Mid poly is a compromise between Low poly and High poly. This mesh works great in cutscenes getting more detailed yet real-time graphics. However, it is mainly used in movie production, where overloading an engine just causes longer render time.
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In case of building up to the full cycle with a detailed model in the end, you better start transforming the blockout into a High poly model. If the aim is to design a lightweight model for a mobile game, you might jump straight into creating Low poly after blocking-out.
Create High poly
You will need High poly on the last stage of the pipeline to transfer details from it to the Low poly model. However, creating it should take place during mesh optimization. There are three primary techniques in designing High poly model:
Subdivision Surface(SubD) relies on dividing the original model into smaller polygons, then calculating the vertices' average position to create new, smoother surfaces.
Sculpting works like a digital version of Play-Doh. This method is highly suitable for modeling soft forms or organics as it makes the mesh so dense that our model becomes smooth and stretchy. While sculpting, you can operate tens and hundreds of millions of polygons.
CAD modeling allows the creation of models with high accuracy. A formula defines each surface, so the model is smooth and easy to edit at any stage. CAD is suitable especially for solid modeling. Engineers use this method to design bridges, cars, robots, and other stuff requiring precision.
Transforming a blockout into Low poly can be as time-consuming as creating High poly. Here is a step-by-step guide to help prioritize your actions. However, don’t hesitate to deviate as this is just one approach among many.
Create a backup: Save a copy of your initial model before starting the optimization process.
Focus on the silhouette: Remove and merge unnecessary vertices and edges while carefully maintaining the model's overall shape.
Eliminate hidden geometry: Delete hidden polygons and non-visible elements like backwalls to optimize the model.
Soften sharp angles: Add or modify geometry to smooth overly sharp angles on the silhouette, enhancing the model's visual appeal.
Keep hard edges intact: Be cautious when altering geometry around hard edges or creases to maintain the model's intended appearance.
Simplify flat objects: Remove or integrate unneeded flat objects into adjacent geometry to save polygons. Don’t worry as they will come later as textures transferred from High poly.
Optimize cylindrical shapes: Ensure cylinders have a multiple of four faces, adjusting the face count based on the object's size. For example, a water tower may have 48 faces, while a cup should stick with 10 or near it.
Arrange intersecting elements: Position intersecting elements to balance visual appeal and efficiency. Avoid too-close placements that may cause visible seams, and prevent excessive overlap that complicates texturing later.
Evenly distribute triangles: Avoid high-density areas and long, thin triangles. Use larger planar faces for flat surfaces to optimize the model.
Practice. There is no other way to fully comprehend the process without going through it several times. So, grab the blockout and keep refining it until you get the desired result.
If Low poly is sufficient, you can continue to create them from here. However, if you want to master the whole pipeline and learn to model detailed and textured 3D models, move forward with this complete guide: