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Howto:Shader programming in FlightGear

457 bytes added, 20:56, 1 September 2019
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Effects file: added link to new page
{{forum|47|Effects & Shaders}}
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This is meant to become an introduction to '''shader programming in FlightGear''', for the time being (03/2010), this is work in progress, please feel free to ask questions or suggest topics.
User defined functions are supported, and a wide variety of commonly used functions are provided built-in as well. This allows the graphics card manufacturer the ability to optimize these built-in functions at the hardware level if they are inclined to do so. Many of these functions are similar to those found in the math library of the C programming language such as <code>exp()</code> and <code>abs()</code> while others are specific to graphics programming such as <code>smoothstep()</code> and <code>texture2D()</code>.
 
== Error Reports, Debugging, Troubleshooting ==
 
Shaders are compiled at FG startup.
 
Shader compilation errors can be found in the fgfs.log file. More about the [[Commonly_used_debugging_tools#fgfs.log|fgfs.log here]].
 
As of FG 2016.4.4, shaders do not seem to recompile upon Debug/Reload Aircraft Model or File/Reset. So the only option to re-compile/test a shader is to quit a re-start FG altogether.
== Shader types ==
In FlightGear, these files can be found in the <code>Shaders</code> subdirectory of the base package, in essence <code>$FG_ROOT/Shaders</code>.
For a list of currently available shaders, you may want to take a look at: http://gitorious.org/{{fg/fgdata/trees/master/root file|Shaders}}.
So, shaders generally go around in pairs - one shader (the ''vertex shader'') is a short program that takes in one vertex from the main CPU and produces one vertex that is passed on to the GPU rasterizer which uses the vertices to create triangles - which it then chops up into individual pixel-sized fragments.
=== Effects file ===
The effects file is the mechanism we use to combine and manipulate all the necessary data to create stunning visual effects. It's the link between the data contained and produced in Nasal, XML and the property tree and the graphics rendering pipeline. It's there to allow us to create these affects without having to know or use the C++ code base. Its flexible framework allows for an almost infinite range of sophisticated effects.
 
See this page for more details: [[Effect Framework]]
==== Parameters ====
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