OptiFine

OptiFine is a mod created many years ago by sp614x. It was designed to overhaul Minecraft's lighting and rendering systems to increase their efficiency and detail. OptiFine is a purely client-side mod, and will crash if loaded by a server. As with all mods intended to improve performance, although it is rare, it is possible for it to decrease performance. As a related point, a small number of mods use custom-made rendering systems that may not work alongside OptiFine. For copyright reasons, OptiFine cannot be redistributed from any locations other than its Minecraft Forum thread and optifine.net. However, because of its general performance improvements, its use is highly recommended for most mod packs. OptiFine is compatible with Fastcraft, and using them together is also recommended for most mod packs.

OptiFine is somewhat unique among mods in that it is not actually reliant upon Minecraft Forge. It can be added to a Forge mod pack as any other mod, but it can also be manually installed into an un-modified Minecraft .jar file. As a result, OptiFine is almost always one of the first mods to advance to new Minecraft versions (although its initial releases are usually incompatible with subsequent initial Forge releases).

OptiFine adds two new Control hotkeys as well: a "Zoom" key and a "Cinematic Camera" key. The Zoom control (default LControl), when held, zooms in the camera significantly, akin to the effect gained by the user of a scoped weapon in a first-person shooter. The Zoom control is very useful for both scouting and Bow aiming. The Cinematic Camera key (default None) causes the camera to actually have inertia. Moving the mouse no longer simply whips the camera around, it causes the camera to smoothly turn in the direction of the movement. Cinematic Camera is automatically used whenever the Zoom control is held, but otherwise its usefulness is somewhat limited.

Many of OptiFine's visual and performance enhancements can be configured through Video Settings in the Options menu. Listed below are OptiFine's various features.
 * Smooth Lighting becomes a percentage, rather than simply being a toggle.
 * Fog gains a quality toggle as well as a start range toggle.
 * The Render Distance slider is expanded substantially, allowing for render distances up to 32 Chunks.
 * Smooth and Multi-Core Chunk Loading options are added. These attempt to reduce the FPS loss incurred by loading and rendering new chunks.
 * An option is added to cause Water to render transparently, allowing users to actually see the bottoms of rivers they are standing near.
 * Options are added to cause Snow to render under Fences and Snow and Grass to visually cover full blocks rather than just their top sides.
 * An option is added to cause plants and water in Swamps to render darker.
 * An option is added to smooth the color transitions on Biome borders into gradients, so that adjacent grass and leaves are not abruptly completely different colors.
 * The "Natural Textures" option causes walls of identical blocks to alternate their normal textures with rotated and flipped versions of their textures, to break up the monotous gridlike nature of such walls.
 * The "Fast Math" option tries to use more optimized rendering functions to further increase FPS.
 * The "Fast Render" option uses completely different rendering algorithms altogether to decrease processing load and attempt to significantly increase FPS. However, Fast Render can cause the textures of some blocks to flicker.
 * The "Chunk Updates" setting changes the number of chunks updates that occur in between each frame generated. Higher settings will cause the world to render more quickly, but can significantly impact FPS, especially when first loading into a world.
 * The "Dynamic Updates" setting causes more chunk updates to occur when the player is not moving. This causes the world to load and render faster at times when the potential performance impact would be less important.