Update

doom.md

@@ -1,6 +1,6 @@
 # Doom
 
-Doom is a legendary video [game](game.md) released in December [1993](1990s.md), perhaps the most famous video game of all time, the game that popularized the [first person shooter](first_person_shooter.md) genre and shocked by its at the time extremely advanced [3D](pseudo_3D.md) graphics (yes, it was actually 3D) and caused one the biggest revolutions in video game history. It was made by [Id Software](id_software.md), most notably by [John Carmack](john_carmack.md) (graphics + engine programmer) and [John Romero](john_romero.md) (tool programmer + level designer). Doom is sadly [proprietary](proprietary.md), it was originally distributed as [shareware](shareware.md) (a free "demo" was available for playing and sharing with the option to buy a full version). However the game engine was later (1999) released as [free (as in freedom) software](free_software.md) under [GPL](gpl.md) which gave rise to many source [ports](port.md). The assets remain non-free but a completely free alternative is offered by the [Freedoom](freedoom.md) project that has created [free as in freedom](free_culture.md) asset replacements for the game. [Anarch](anarch.md) is an official [LRS](lrs.md) game inspired by Doom, completely in the [public domain](public_domain.md).
+Doom is a legendary video [game](game.md) released in December [1993](1990s.md), perhaps the most famous video game of all time, the game that popularized the [first "person" shooter](first_person_shooter.md) genre and shocked by its at the time extremely advanced [3D](pseudo_3D.md) graphics (yes, **Doom is 3D**) and caused one the biggest revolutions in video game history. It was made by [Id Software](id_software.md), most notably by [John Carmack](john_carmack.md) (graphics + engine programmer) and [John Romero](john_romero.md) (tool programmer + level designer). Doom is sadly [proprietary](proprietary.md), it was originally distributed as [shareware](shareware.md) (a free "demo" was available for playing and sharing with the option to buy a full version). However the game engine was later (1999) released as [free (as in freedom) software](free_software.md) under [GPL](gpl.md) which gave rise to many source [ports](port.md) and "improved" "[modern](modern.md)" engines (which however look like shit, the original looks by far the best, if you want to play Doom use Chocolate Doom or Crispy Doom, avoid anything with GPU rendering). The assets remain non-free but a completely free alternative is offered by the [Freedoom](freedoom.md) project that has created [free as in freedom](free_culture.md) asset replacements for the game. [Anarch](anarch.md) is an official [LRS](lrs.md) game inspired by Doom, completely in the [public domain](public_domain.md).
 
 { Great books about Doom I can recommend: *Masters of Doom* (about the development) and *Game Engine Black Book: Doom* (details about the engine internals). ~drummyfish }
 
@@ -10,10 +10,14 @@ The major leap that Doom engine's graphics brought was unprecedented, however Do
 
 The game's backstory was simple and didn't stand in the way of gameplay, it's basically about a tough marine (so called *Doomguy*) on a Mars military base slaying hordes of demons from hell, all in a rock/metal style with a lot of gore and over-the-top violence (chain saws n stuff).
 
-LOL someone created a Doom system monitor for [Unix](unix.md) systems called [psDooM](psdoom.md) where the monsters in game are the operating system [processes](process.md) and killing the monsters kills the processes.
-
 Doom was followed by Doom II in 1995, which "content-wise" was basically just a data disc, the same game with new levels and some minor additions. Later there were some other releases and rereleases, notable is Doom III from 2004, Doom 2016 ("reboot") and Doom: Eternal (2020).
 
+Some **[interesting](interesting.md) things** about Doom:
+
+- Someone created a Doom system monitor for [Unix](unix.md) systems called [psDooM](psdoom.md) where the monsters in game are the operating system [processes](process.md) and killing the monsters kills the processes.
+- Someone (kgsws) has been [hacking](hacking.md) the ORIGINAL Doom engine in an impressive way WITHOUT modifying the source code or the binary, rather using [arbitrary code execution](arbitrary_code_execution.md) bug; he added very advanced features known from newer source ports, for example an improved 3D rendering algorithms allowing geometry above geometry etc. (see e.g. https://yt.artemislena.eu/watch?v=RdbRPNPUWlU).
+- TODO
+
 ## Doom Engine/Code
 
 *See also [game engine](game_engine.md) for the list of different Doom engines.*
@@ -22,7 +26,7 @@ Doom source code is written in [C89](c.md) and is about 36000 [lines of code](lo
 
 The game only used [fixed point](fixed_point.md), no [float](float.md)!
 
-The **Doom engine** was revolutionary and advanced (not only but especially) video game graphics by a great leap, considering its predecessor [Wolf3D](wolf3D.md) was really primitive in comparison (Doom basically set the direction for future trends in games such as driving the development of more and more powerful [GPUs](gpu.md) in a race for more and more impressive visuals). Doom used a technique called **[BSP rendering](bsp.md)** (levels were made of convex 2D sectors that were then placed in a BSP tree which helped quickly sort the walls for rendering front-to-back) that was able to render [realtime](realtime.md) 3D views of textured (all walls, floors and ceilings) environments with primitive lighting (per-sector plus diminishing lighting), enemies and items represented by 2D [billboards](billboard.md) ("[sprites](sprite.md)"). No [GPU](gpu.md) acceleration was used, graphics was rendered purely with [CPU](cpu.md) (so called [software rendering](sw_rendering.md), GPU rendering would come with Doom's successor [Quake](quake.md), and would also later be brought to Doom by newer community made engines, though the original always looks the best). This had its limitations, for example the camera could not look up and down, there could be no tilted walls and the levels could not have rooms above other rooms. The geometry of levels was only static, i.e. it could not change during play (only height of walls could), because rendering was dependent on precomputed BSP trees (which is what made it so fast). For these reasons some call Doom "[pseudo 3D](pseudo3d.md)" or 2.5D rather than "true 3D". Nevertheless, though with limitations, Doom did present 3D views and internally it did work with 3D coordinates (for example the player or projectiles have 2D position plus height coordinate), despite some dumb YouTube videos saying otherwise. For this reason we prefer to call Doom a **primitive 3D** engine, but 3D nonetheless. Other games later used the Doom engine, such as Heretic, Hexen and Strife. The Doom engine was similar to and competing with [Build](build_engine.md) engine that ran games like [Duke Nukem 3D](duke_3d.md), Blood and Shadow Warrior. All of these 90s shooters were amazing in their visuals and looked far better than any [modern](modern.md) shit. Build engine games had similar limitations to those of the Doom engine but would improve on them (e.g. faking looking up and down by camera tilting, which could in theory be done in Doom too, or allowing sloped floor and dynamic level geometry).
+The **Doom engine** was revolutionary and advanced (not only but especially) video game graphics by a great leap, considering its predecessor [Wolf3D](wolf3D.md) was really primitive in comparison (Doom basically set the direction for future trends in games such as driving the development of more and more powerful [GPUs](gpu.md) in a race for more and more impressive visuals). Doom used a technique called **[BSP rendering](bsp.md)** (levels were made of convex 2D sectors that were then placed in a BSP tree which helped quickly sort the walls for rendering front-to-back) that was able to render [realtime](realtime.md) 3D views of textured (all walls, floors and ceilings) environments with primitive lighting (per-sector plus diminishing lighting), enemies and items represented by 2D [billboards](billboard.md) ("[sprites](sprite.md)"). No [GPU](gpu.md) acceleration was used, graphics was rendered purely with [CPU](cpu.md) (so called [software rendering](sw_rendering.md), GPU rendering would come with Doom's successor [Quake](quake.md), and would also later be brought to Doom by newer community made engines, though the original always looks the best). This had its limitations, for example the camera could not look up and down, there could be no tilted walls and the levels could not have rooms above other rooms. The geometry of levels was only static, i.e. it could not change during play (only height of walls could), because rendering was dependent on precomputed BSP trees (which is what made it so fast). For these reasons some call Doom "[pseudo 3D](pseudo3d.md)" or 2.5D rather than "true 3D", some retards took this even as far as calling Doom 2D with its graphics being just an "illusion", as if literally every 3D graphics ever wasn't a mere illusion. Nevertheless, though with limitations, Doom did present 3D views and internally it did work with 3D coordinates (for example the player or projectiles have 2D position plus height coordinate), despite some dumb YouTube videos saying otherwise. For this reason we prefer to call Doom a **primitive 3D** engine, but 3D nonetheless. Other games later used the Doom engine, such as Heretic, Hexen and Strife. The Doom engine was similar to and competing with [Build](build_engine.md) engine that ran games like [Duke Nukem 3D](duke_3d.md), Blood and Shadow Warrior. All of these 90s shooters were amazing in their visuals and looked far better than any [modern](modern.md) shit. Build engine games had similar limitations to those of the Doom engine but would improve on them (e.g. faking looking up and down by camera tilting, which could in theory be done in Doom too, or allowing sloped floor and dynamic level geometry).
 
 Indexed ([palette](palette.md)) mode with "only" 256 colors was used for rendering. Precomputed color tables were used to make dimming of colors faster.