HA7 Task 6 Constraints

Polygon moddeling 
In 3D computer graphics, polygonal modeling is an approach for modeling objects by representing or approximating their surfaces using polygons. Polygonal modeling is well suited to scanline rendering and is therefore the method of choice for real-time computer graphics. Alternate methods of representing 3D objects include NURBS surfaces, subdivision surfaces, and equation-based representations used in ray tracers. See polygon mesh for a description of how polygonal models are represented and stored.


Triangle Modeling 
The polygon count that's reported in a modelling app is always misleading, because a model's triangle count is higher. It's usually best therefore to switch the polygon counter to a triangle counter in your modelling app, so you're using the same counting method everyone else is using.

Polygons however do have a useful purpose in game development. A model made of mostly four-sided polygons (quads) will work well with edge-loop selection & transform methods that speed up modelling, make it easier to judge the "flow" of a model, and make it easier to weight a skinned model to its bones. Artists usually preserve these polygons in their models as long as possible. When a model is exported to a game engine, the polygons are all converted into triangles automatically. 

Triangle Count vs. Vertex Count
Vertex count is ultimately more important for performance and memory than the triangle count, but for historical reasons artists more commonly 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 and so on. However, seams in UVs, changes to shading/smoothing groups, and material changes from triangle to triangle etc. are all treated as a physical break in the model's surface, when the model is rendered by the game. The vertices must be duplicated at these breaks, so the model can be sent in renderable chunks to the graphics card.

http://wiki.polycount.net/PolygonCount

Rendering Time
Rendering is the final process of creating the actual 2D image or animation from the prepared scene. This can be compared to taking a photo or filming the scene after the setup is finished in real life. Several different, and often specialised, rendering methods have been developed. These range from the distinctly non-realistic wireframe rendering through polygon-based rendering, to more advanced techniques such as: scanline rendering, ray tracing, or radiosity. Rendering may take from fractions of a second to days for a single image/frame. In general, different methods are better suited for either photo-realistic rendering, or real-time rendering.

Rendering for interactive media, such as games and simulations, 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. The primary goal is to achieve an as high as possible degree of photorealism at an acceptable minimum rendering speed (usually 24 frames per second, as that is the minimum the human eye needs to see to successfully create the illusion of movement). In fact, 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. 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. Non-real time rendering enables the leveraging of limited processing power in order to obtain higher image quality. Rendering times for individual frames may vary from a few seconds to several days for complex scenes. Rendered frames are stored on a hard disk then can be transferred to other media such as motion picture film or optical disk. These frames are then displayed sequentially at high frame rates, typically 24, 25, or 30 frames per second, to achieve the illusion of movement.