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raycasting.md

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 # Raycasting
 
-In [computer graphics](graphics.md) raycasting refers to a rendering technique in which we determine which parts of the scene should be drawn according to which parts of the scene are hit by rays cast from the camera. This is based on the idea that we can trace rays of light that enter the camera by going backwards, i.e. starting from the camera towards the parts of the scene that reflected the light. The term raycasting specifically has two main meanings:
+In [computer graphics](graphics.md) raycasting refers to a rendering technique in which we determine which parts of the scene should be drawn according to which parts of the scene are hit by rays cast from the camera; it is a simpler version of **[raytracing](raytracing.md)**. The whole idea is based on the observation that we can trace rays of light that enter the camera by going BACKWARDS, i.e. instead of tracing light from light sources we rather start from the camera and go towards the parts of the scene that reflected the light (by which we ensure we are only considering the RELEVANT paths of light that actually end up hitting the camera) -- that is we are asking the question "in order for this screen pixel to light up, where would the light be coming from?", and then computing the answer to the question. A simplified way to quickly imagine what's going on is therefore to think of drawing the scene via "scanning" it with some kind of laser beam. Despite perhaps sounding intimidating at first, raycasting is one of the [simplest](minimalism.md) rendering methods, and for that it is also quite elegant -- [we](lrs.md) definitely do recommend it.
 
-- **[3D](3d.md) raycasting**: [Algorithm](algorithm.md) that works the same as [raytracing](raytracing.md) but without [recursion](recursion.md). I.e. raycasting is simpler than raytracing and only casts primary rays (those originating from the camera), hence, unlike in raytracing, there are no shadows, reflections and refractions. Raytracing is the extension of raycasting.
-- **[2D](2d.md) raycasting**: Technique for rendering so called "[pseudo3D](pseudo3D.md)" (primitive 3D) graphics, probably best known from the old [game](game.md) Wolf3D (predecessor of [Doom](doom.md)). The principle of casting the rays is the same but we only limit ourselves to casting the rays within a single 2 dimensional plane and render the environemnt by columns (unlike the 3D variant that casts rays and renders by individual pixels).
+Raycasting is an **image order** rendering method, meaning that we iterate over the pixels of the screen and for each determine its [color](color.md) (as opposed to object order methods that iterate over 3D objects that are then "pasted" to the screen). I.e. the image can be drawn in any order -- let's say from top left to bottom right -- and without drawing any pixel more than once or leaving out any. This is advantageous as we may leave out [double buffering](double_buffering.md) and save A LOT of memory on the extra frame buffer. We may also utilize for example [frameless rendering](frameless.md). All these attributes are why we consider raycasting so nice.
+ 
+Now it's important to mention that among graphics programmers the term raycasting has come to have two meanings:
+
+- **[3D](3d.md) raycasting**: Casts a ray for each pixels of the screen. I.e. this works the same as traditional [raytracing](raytracing.md) but without [recursion](recursion.md). I.e. raycasting is simpler than raytracing and only casts so called primary rays (those originating from the camera), hence, unlike in raytracing, there are no shadows, reflections and refractions. So raytracing is the extension of raycasting. Similarly to raytracing this kind of raycasting is considered slow as it requires casting screen width times screen height rays (one for each pixel) every frame, but it must be said this is a lot due to fact that [GPUs](gpu.md) are built for different kind of rendering, so raycasting many times ends up being implemented in [software](sw_rendering.md). As an image order method there is actually a good potential for raycasting to be [parallelized](parallelism.md) (the rays may in theory be cast simultaneously), so with special hardware raycasting could be quite fast. With nice tricks and [optimizations](optimization.md) (hierarchical accelerating structures, subsampling, mathematically simple shapes, ...) however even software raycasting may be used for real time rendering.
+- **[2D](2d.md) raycasting** (also called 1D raycasting): Technique for rendering so called "[pseudo3D](pseudo3D.md)" (primitive 3D) graphics, probably best known from the old [game](game.md) [Wolf3D](wolf3d.md) (predecessor of [Doom](doom.md)), also used in [Anarch](anarch.md). The principle of casting the rays is still the same but we only limit ourselves to casting them within a single 2 dimensional plane and render the environemnt by columns (unlike the 3D variant that casts rays and renders by individual pixels). I.e. we are [cheating](cheating.md) a bit -- instead of casting a ray for each screen pixel we only cast a ray for each screen COLUMN and so we reduce the full 3D raycasting into a fewer dimensional one and use clever tricks to still keep it looking "3D". Of course this introduces some limitation (like not being able to rotate camera up and down) but makes the method MUCH faster -- so fast it was used for real time "3D" rendering on the early 90s computers. Additionally this method may be greatly improved to make it yet more awesome -- for example it's possible to add some verticality to the environments by casting a few extra rays for each column.
+
+**If it's so awesome, why isn't it used in the [mainstream](mainstream.md)?** As always because mainstream is [shit](shit.md) -- it rather settled on the more ugly but business friendly rasterization of polygonal models -- probably the main reason is that with rasterization companies can split people into graphics programmers, who just program a rasterizer, and graphic artists, who can make whatever 3D model out of polygons without caring about technical details. Raycasting is more of an [art](art.md) requiring individual tweaks to each program and considering the technical side when making the 3D models. [Capitalism](capitalism.md) does ugly things to produce huge quantities of products to be [consumed](consumerism.md), it never cares about efficiency, elegance or beauty of art.
 
 ## 2D Raycasting