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OpenGL is a programming interface that allows software to interact with graphics hardware and create 3D scenes. Using 2D techniques, it can improve performance and ease of programming. It is widely accepted and can be used on a variety of systems, but can be more complex than traditional 2D programming. It requires a graphics card for increased rendering speed and does not provide native support for displaying text.
The Open Graphics Library® (OpenGL®) is primarily a programming interface that allows software applications to interact with graphics hardware and create three-dimensional (3D) scenes quickly and efficiently. Using two-dimensional (2D) OpenGL® programming techniques, the hardware acceleration provided by the library can improve the performance and, at times, the ease of programming of software that does not necessarily use 3D models or transforms. The most common method for using 2D OpenGL® is to draw quadrilaterals, or rectangles, that are textured with an image, effectively creating an object in 3D space from an image. Once established, these quadrilaterals can be manipulated, either by rigorous 2D methods, or by transforming them with 3D matrices for special effects that would otherwise be difficult to achieve with 2D raster graphics alone. There are some complications that come with using a 3D library when using it only for 2D graphics, including hyper-precision which can make it difficult to isolate single pixel locations, as well as requiring 3D hardware support for a program which may not require it.
Many hardware and software developers provide custom abstract programming interfaces (APIs) and drivers that make their particular products fully compatible with the OpenGL® library. This widespread acceptance of an open standard gives programmers a way to directly access hardware on a wide variety of systems. The hardware acceleration provided when using 2D OpenGL® can allow a program to run more smoothly than would otherwise be possible. This speed is balanced by the fact that using the OpenGL® pipeline for graphics can be very different from using traditional 2D programming methods which generally don’t use a state machine model like OpenGL® does.
Most 2D OpenGL® programs use flat rectangles made to the same aspect ratio as a texture image to portray graphics. This has the advantage of being very fast to render, as well as simplifying programming to use some of the same logic as raster-based buffered graphics. Some effects, such as scaling an image, rotating an image, or inverting an image, can actually be done much more efficiently using OpenGL®.
There are a few factors that can make 2D OpenGL® programs more complex than other 2D programs might normally be. One such factor is the pixel accuracy on the display. OpenGL® does not equate a part of the virtual coordinate system to a pixel on a screen, as raster graphics do, so it is sometimes necessary to use floating point numbers for screen coordinates to avoid gaps in the display or strange pixel placements .
Another problem is that OpenGL® requires the use of a graphics card to increase rendering speed. If an application uses OpenGL® for displaying an interface or system window, devices that do not have graphics acceleration may experience a performance loss for graphics that may seem very simple to an end user. OpenGL also doesn’t provide any native support for displaying text, which means that displaying large areas of text may require a fair amount of custom code.
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