HA7 Task 6 - Constraints

The two common measurements of a game model are polygon count and vertex count. 

Polygon count of a model is really the triangle count. Games use triangles instead of polygons because the most modern graphic hardware is built to accelerate the rendering of triangles, so its renders quicker with triangles. 

When a model is exported to a game engine, the polygons are all converted into triangles so the triangles are counted now. However different tools will create different triangle layouts within those polygons for example, a quadrilateral can end up as either a "ridge" or a "valley" depending how its triangulated. 

Vertex count is more important for performance and memory than triangle count but more 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, 4 triangles use 6 vertices and so on.

File Size 

File size measures the size of a computer file. Typically it is measured in bytes. The actual amount of disk space consumed by the file depends on the file system. The maximum file size a file system supports depends on the number of bits reserved to store size information and the total size of the file system.

Rendering time 

Rendering is the process of creating the actual 2D image or animation from the prepared scene. This is like taking a photo after the setup is finished in real life. There are different rendering methods that have been developed that range from non-realistic wireframe rendering through polygon based rendering to more advanced techniques such as scan line rendering. Rendering can take second to days to complete depending on the method. 

Real time 

"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, exploitation 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. These effects can lend an element of realism to a scene, even if the effect is merely a simulated artifact of a camera. This is the basic method employed in games, interactive worlds and VRML. The rapid increase in computer processing power has allowed a progressively higher degree of realism even for real-time rendering, including techniques such as HDR rendering. Real-time rendering is often polygonal and aided by the computer's GPU."

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."

The difference between the two is really just real time rendering is used for games or interactive media, basically anything where you can look around using the camera, the quality isn't as good as non real time but it renders faster than non real time.