Document the blit shaders

shaders/gles2/blit-gamma.fs.glsl

@@ -8,15 +8,20 @@
 // option. This file may not be copied, modified, or distributed
 // except according to those terms.
 
-/// Blits a texture, applying gamma correction.
+//! Blits a texture, applying gamma correction.
 
 precision mediump float;
 
+/// The source texture to blit.
 uniform sampler2D uSource;
 
+/// The approximate background color, in linear RGB.
 uniform vec3 uBGColor;
+
+/// The gamma LUT.
 uniform sampler2D uGammaLUT;
 
+/// The incoming texture coordinate.
 varying vec2 vTexCoord;
 
 void main() {

shaders/gles2/blit-linear.fs.glsl

@@ -8,12 +8,14 @@
 // option. This file may not be copied, modified, or distributed
 // except according to those terms.
 
-/// A trivial shader that does nothing more than blit a texture.
+//! A trivial shader that does nothing more than blit a texture.
 
 precision mediump float;
 
+/// The source texture to blit.
 uniform sampler2D uSource;
 
+/// The incoming texture coordinate.
 varying vec2 vTexCoord;
 
 void main() {

shaders/gles2/blit.vs.glsl

@@ -8,21 +8,23 @@
 // option. This file may not be copied, modified, or distributed
 // except according to those terms.
 
-/// A trivial shader that does nothing more than blit a texture.
+//! A trivial shader that does nothing more than blit a texture.
 
 precision mediump float;
 
 /// A 3D transform to apply to the scene.
 uniform mat4 uTransform;
-/// A fixed scaling to be applied to the texture coordinates.
+
+/// A pair of fixed scale factors to be applied to the texture coordinates.
 uniform vec2 uTexScale;
 
 /// The 2D vertex position.
 attribute vec2 aPosition;
+
 /// The texture coordinate.
 attribute vec2 aTexCoord;
 
-/// The scaled texture coordinate.
+/// The outgoing texture coordinate.
 varying vec2 vTexCoord;
 
 void main() {