diff --git a/src/autoreplace_gui.cpp b/src/autoreplace_gui.cpp
index deadcdd0af..29bf638e82 100644
--- a/src/autoreplace_gui.cpp
+++ b/src/autoreplace_gui.cpp
@@ -105,11 +105,11 @@ class ReplaceVehicleWindow : public Window {
 	GroupID sel_group;
 	static RailType sel_railtype;
 
-	/** Figure out if an engine should be added to a list
-	 * @param e The EngineID
-	 * @param draw_left If true, then the left list is drawn (the engines specific to the railtype you selected)
-	 * @param show_engines if truem then locomotives are drawn, else wagons (never both)
-	 * @return true if the engine should be in the list (based on this check)
+	/** Figure out if an engine should be added to a list.
+	 * @param e            The EngineID.
+	 * @param draw_left    If \c true, the the left list is drawn (the engines specific to the railtype you selected).
+	 * @param show_engines If \c true, the locomotives are drawn, else the wagons are drawn (never both).
+	 * @return \c true if the engine should be in the list (based on this check), else \c false.
 	 */
 	bool GenerateReplaceRailList(EngineID e, bool draw_left, bool show_engines)
 	{
diff --git a/src/gfx_func.h b/src/gfx_func.h
index dd7693f93a..70286ee69d 100644
--- a/src/gfx_func.h
+++ b/src/gfx_func.h
@@ -146,7 +146,7 @@ void SortResolutions(int count);
 bool ToggleFullScreen(bool fs);
 
 /* gfx.cpp */
-extern FontSize _cur_fontsize;
+extern FontSize _cur_fontsize; ///< Currently selected font.
 
 byte GetCharacterWidth(FontSize size, uint32 key);
 
@@ -162,8 +162,13 @@ static inline byte GetCharacterHeight(FontSize size)
 	return _font_height[size];
 }
 
+/** Height of characters in the small (#FS_SMALL) font. */
 #define FONT_HEIGHT_SMALL  (GetCharacterHeight(FS_SMALL))
+
+/** Height of characters in the normal (#FS_NORMAL) font. */
 #define FONT_HEIGHT_NORMAL (GetCharacterHeight(FS_NORMAL))
+
+/** Height of characters in the large (#FS_LARGE) font. */
 #define FONT_HEIGHT_LARGE  (GetCharacterHeight(FS_LARGE))
 
 extern DrawPixelInfo *_cur_dpi;
diff --git a/src/gfx_type.h b/src/gfx_type.h
index 569c78214d..7796d19e0f 100644
--- a/src/gfx_type.h
+++ b/src/gfx_type.h
@@ -129,6 +129,7 @@ struct CursorVars {
 	bool vehchain;   ///< vehicle chain is dragged
 };
 
+/** Data about how and where to blit pixels. */
 struct DrawPixelInfo {
 	void *dst_ptr;
 	int left, top, width, height;
@@ -136,6 +137,7 @@ struct DrawPixelInfo {
 	ZoomLevel zoom;
 };
 
+/** Structure to access the alpha, red, green, and blue channels from a 32 bit number. */
 struct Colour {
 #if TTD_ENDIAN == TTD_BIG_ENDIAN
 	uint8 a, r, g, b; ///< colour channels in BE order
@@ -143,7 +145,7 @@ struct Colour {
 	uint8 b, g, r, a; ///< colour channels in LE order
 #endif /* TTD_ENDIAN == TTD_BIG_ENDIAN */
 
-	operator uint32 () const { return *(uint32 *)this; }
+	operator uint32 () const { return *(uint32 *)this; } ///< Conversion of the channel information to a 32 bit number.
 };
 
 /** Available font sizes */