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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. We may also say it's a simpler version of the popular algorithm called **[raytracing](raytracing.md)**, or perhaps that raycasting is the initial idea of rendering via casting rays, which subsequently inspires many improvements and extensions like recursive rays (raytracing), [Monte Carlo](monte_carlo.md) sampling (pathtracing), using cones instead of lines (conetracting) etc. 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 originating from the camera -- of course we do this [mathematically](math.md), using [analytic geometry](analytic_geometry.md), i.e. finding intersections of the rays with geometric shapes by solving algebraic equations. 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.
+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 virtual rays cast from the camera. We may also say it's a simpler version of the popular algorithm called **[raytracing](raytracing.md)**, or perhaps that raycasting is the initial idea of rendering via casting rays, which subsequently inspires many improvements and extensions like recursive rays (raytracing), [Monte Carlo](monte_carlo.md) sampling (pathtracing), using cones instead of lines (conetracting) etc. 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 originating from the camera -- of course we do this [mathematically](math.md), using [analytic geometry](analytic_geometry.md), i.e. finding intersections of the rays with geometric shapes by solving algebraic equations. 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.
 
 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.