Tiled rendering

Tiled rendering is the process of subdividing a computer graphics image by a regular grid in optical space and rendering each section of the grid, or tile, separately. The advantage to this design is that the amount of memory and bandwidth is reduced compared to immediate mode rendering systems that draw the entire frame at once. This has made tile rendering systems particularly common for low-power handheld device use. Tiled rendering is sometimes known as a "sort middle" architecture, because it performs the sorting of the geometry in the middle of the graphics pipeline instead of near the end. Creating a 3D image for display consists of a series of steps. First, the objects to be displayed are loaded into memory from individual models. The system then applies mathematical functions to transform the models into a common coordinate system, the world view. From this world view, a series of polygons (typically triangles) is created that approximates the original models as seen from a particular viewpoint, the camera. Next, a compositing system produces an image by rendering the triangles and applying textures to the outside. Textures are small images that are painted onto the triangles to produce realism. The resulting image is then combined with various special effects, and moved into a frame buffer, which video hardware then scans to produce the displayed image. This basic conceptual layout is known as the display pipeline. Each of these steps increases the amount of memory needed to hold the resulting image. By the time it reaches the end of the pipeline the images are so large that typical graphics card designs often use specialized high-speed memory and a very fast computer bus to provide the required bandwidth to move the image in and out of the various sub-components of the pipeline. This sort of support is possible on dedicated graphics cards, but as power and size budgets become more limited, providing enough bandwidth becomes expensive in design terms.