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+## Purpose
+GLSL shader support exists to be compatible in case [[Cg shaders]] cannot be supported, which is the case for OpenGL ES, and EGL contexts ([[KMS mode]] in Linux for one).
+
+Like Cg shaders, GLSL shaders represent a single pass, and requires a preset file to describe how multiple shaders are combined. The extension is .glsl. The internal format of the shaders are the same as modern [[XML shaders]].
+
+As GLSL shaders are normally placed in two different files (vertex, fragment), making it very impractical to select in a menu. This is worked around by using compiler defines in order to be equivalent to Cg shaders.
+
+### Example GLSL shader
+    varying vec2 tex_coord;
+    #if defined(VERTEX)
+        attribute vec2 TexCoord;
+        attribute vec2 VertexCoord;
+        uniform mat4 MVPMatrix;
+        void main()
+        {
+            gl_Position = MVPMatrix * vec4(VertexCoord, 0.0, 1.0);
+            tex_coord = TexCoord;
+        }
+    #elif defined(FRAGMENT)
+        uniform sampler2D Texture;
+        void main()
+        {
+            gl_FragColor = texture2D(Texture, tex_coord);
+        }
+    #endif
+
+GLSL shaders must be modern style, and using `ruby` prefix is discouraged.
+
+## Converting from Cg shaders
+GLSL shaders are mostly considered a compatibility format. It is possible to compile Cg shaders into GLSL shaders automatically using our `cg2glsl` script found [here](https://github.com/Themaister/RetroArch/blob/master/tools/cg2glsl.py). It can convert single shaders as well as batch conversion.
+
+It relies on nVidia's `cgc` tool found in `nvidia-cg-toolkit` package.
+
+## GLSL preset
+Like [[Cg shaders]], there is a preset format. Instead of .cgp extension, .glslp extension is used. The format is exactly the same, just replace .cg shaders with .glsl. To convert a .cgp preset, rename to .glslp and replace all references to .cg shaders with .glsl.
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