HA4 Task 6 – Constraints

What constraints are involved in working within a 3D environment - polygon count, file size and rendering time?

Remember that you are trying to comprehensively explain the theory and applications of 3D with elucidated examples and consistently using subject terminology correctly.

Polygon Count And File Size - Two common measurements of an object's 'cost’ or file size are the polygon count and vertex count. E.g. a game character may stretch anywhere from 200-300 polygons, to 40,000+ polygons. A high-end third-person console or PC game may use a bunch of vertices or polygons for each character and an IOS tower defense game might use very few per character.



Polygonal Vs Triangles - Games almost always use triangles and not polygons because most modern graphic hardware is built to accelerate the rendering of triangles. However, the polygon count that's reported in a modelling app is always misleading. This is partly because a model's triangle count is increasingly higher. It's usually best therefore to switch the polygon counter to a triangle counter when you have chance in your modelling app; so you're using the same counting method everyone else is using. Polygons also do have a useful purpose in game development. A model made of mostly four-sided polygons, will work well with edge-loop selection and transform methods that speed up modelling. However, different tools will create different triangle layouts within those polygons. A quad (4 Sided Polygon) can end up either as a "ridge" or as a "valley" depending on how it's triangulated. In contrast, artists need to carefully examine a new model in the game engine to see if the triangle edges are turned the way they are intended to be. If not, certain polygons can then be triangulated manually. 




Triangle Count Vs Vertex Count - Vertex count is far more important for performance and memory than the triangle count, but for historical reasons, artists more frequently use triangle count as a performance measurement. On the most basic level, the triangle count and the vertex count can be similar if the all the triangles are connected to one another. 1 triangle uses 3 vertices, 2 triangles use 4 vertices, 3 triangles use 5 vertices, and 4 triangles use 6 vertices e.c.t. However, seams in UVs, changes to shading/smoothing groups, and material changes from triangle to triangle etc. This means that they are all treated as a physical break in the model's surface, when the model is rendered by the game.





Rendering Time - Rendering is the final process of creating an actual 2D image or animation from the prepared scene. This can be compared to taking a photo or even filming the scene after the setup is finished in real life. Many different, and often specialised, rendering methods have been developed throughout the years. These range from the distinctly non-realistic wireframe rendering through polygon-based rendering, to more advanced techniques such as scanline rendering.



Real Time - Rendering for interactive media, such as games, is calculated and displayed in real time, at rates of approximately 20 to 120 frames per second. In real-time rendering, the goal is to show as much information as possible as the eye can process in a fraction of a second, i.e. one frame. In fact, in Real Time, exploitations can be applied in the way the eye 'perceives' the world and as a result the final image presented is not necessarily that of the real-world; but one close enough for the human eye to tolerate. In addition, Rendering software may simulate such visual effects as lens flares, depth of field or motion blur. These are attempts to simulate visual phenomena resulting from the optical characteristics of cameras and of the human eye.



Non - Real Time - Animations for non-interactive media, such as feature films and video, are rendered much more slowly than just Real Time. Non-real time rendering enables the leveraging of limited processing power in order to keep hold of higher image quality. Rendering times for individual frames may vary from a few seconds to several days for complex scenes. Also, rendered frames are stored on a hard disk then can be transferred to other media's such as motion picture film or optical disk. Therefor, these frames are then displayed sequentially at high frame rates, typically 24, 25, or 30 frames per second, to achieve the illusion of movement.

Reflection/Scattering - How light interacts with the surface at a given point

Shading - How material properties vary across the surface