Understanding computer graphics is hard. It is even harder to figure out where to start. This guide aims to provide a top-level understanding of common terms and processes that make pictures happen. The examples are implemented using Blender and Unreal Editor and do not require any programming or art skills.

Vertices

Vertices are an important building block of computer graphics. A vertex is a single point in a virtual space that can be implemented in multiple different ways. The most basic version of a vertex in a 3d space consists only of the values X, Y, Z that represent its position. Vertices are commonly used to define lists of triangles that represent a 3d mesh because triangles can be easily rendered by GPU programs called shader.

When working with 3d editing software like Blender you will be presented with quads instead of triangles as quads are easier to shape into complex models. The mesh will be automatically triangulated during export to be later used in your game engine.

Back-Face Culling

Triangles have a front-face and a back-face. Usually only triangles facing the player are rendered as this almost halves the number of triangles that have to be rendered on screen. This technique is called back-face culling and leverages the assumption that you shouldn’t be able to see the back-faces of solid 3D objects.

Back-face culling is off: The back-faces of this object are visible and take up valuable resources. This is typically unnecessary as most objects do not have holes in their mesh.
Back-face culling is on: The back-faces of this object are invisible and we render only the outside of the object as we assume that our objects typically don’t let us look inside of them.
The material settings of Unreal Editor allow you to deactivate back-face culling for each material.

UV-Mapping

The first common extension of vertices are a set of texture coordinates usually referred to as UV-coordinates and are used for a process that is called UV-mapping. The two values u and v are ranging from 0 to 1. They reference a point in the 2d space of an image with (0.5, 0.5) representing the center. If you create a triangle in 3d space with 3 distinct UV-coordinates you can visualize that triangle in the textures 2d space. The UV-coordinates for each rendered pixel of the triangle are interpolated and used to look up a specific pixel from a texture in a process called texture-sampling.

UV-coordinates are assigned to a mesh. A shader can use these coordinates to sample the texture.

Normal Maps

The combination of UV-mapping and texture-sampling can also be used to implement normal-maps to create more detailed models without using more vertices. Normal maps are used to ‘bend light with math’. This creates an illusion of bumps and dents that are missing from the mesh.

  • The Texture
  • The Normal Map
  • The Material in Unreal Editor
I created the texture by taking a picture of my coffee table and cropping it into square dimensions. The normal map was based on that texture and created with a process called baking normals using Blender. The added normal map creates the illusion of deep ridges that are not really there. Creating a mesh with that level of detail would require a lot more resources than just adding a normal map.

Texture Masks

UV-Mapping can also be used to implement texture-masks to enable color customization. Masking a texture is similar to setting up the texture itself. You assign texture coordinates to the 3d model and paint the areas you want to mask. The mask acts as a switch between the texture and a dynamically specified color on each rendered pixel. A common RGBA texture mask comes with 4 switches that enable you to blend and combine a total of 5 textures.

  • The Mesh
  • The UV-Map
  • The Texture
  • The Mask
  • The Material in Unreal Editor
The colors of the marked areas of the mesh can be adjusted easily while preserving the rest of the texture. Masking is commonly used in character customization or to color code team members.

Vertex Color

Another common extension of vertices is the addition of a vertex color. A vertex color is usually represented by 1-4 values but can be even higher depending on the use case. Vertex color is used to mix and blend textures on terrains or walls that would otherwise look very stale. This is achieved by associating each value of the vertex color with a different texture and by blending accordingly. This effect works better with models that have lot of vertices as vertex coloring with very simple meshes does not allow for enough details.

  • The Material in Unreal Editor
  • A Vertex Color Visualization
The vertex painting tool in Unreal Editor enables level designer to paint right on the mesh.
A Quick Comparison
Vertex ColoringTexture Masking
– no additional texture required
– quality depends on vertex density
– information stored in vertices
– designed to create endless variations
– used for level design		– information stored in texture
– independent of underlying mesh
– typically one mask per object
– designed for dynamic coloring
– used for gameplay features
Vertex Coloring and Texture Masking both implement texture blending but have different use cases.

This was just a quick peak into the world of rendering techniques. Let me know what you want to see next.

Hope that helps.