Merge branch 'master' into jgrpp

# Conflicts:
#	CMakeLists.txt
#	bin/ai/CMakeLists.txt
#	bin/game/CMakeLists.txt
#	src/ai/ai_info.cpp
#	src/company_base.h
#	src/economy.cpp
#	src/game/game_info.cpp
#	src/gfx_type.h
#	src/linkgraph/linkgraph_gui.cpp
#	src/palette.cpp
#	src/palette_func.h
#	src/saveload/saveload.h
#	src/saveload/vehicle_sl.cpp
#	src/ship_cmd.cpp
#	src/train_cmd.cpp
#	src/vehicle_base.h
#	src/window.cpp
#	src/window_func.h

src/palette.cpp

@@ -25,8 +25,6 @@
 Palette _cur_palette;
 std::mutex _cur_palette_mutex;
 
-byte _colour_gradient[COLOUR_END][8];
-
 byte _colour_value[COLOUR_END] = {
 	133, // COLOUR_DARK_BLUE
 	 99, // COLOUR_PALE_GREEN,
@@ -294,3 +292,38 @@ TextColour GetContrastColour(uint8_t background, uint8_t threshold)
 	/* Compare with threshold brightness which defaults to 128 (50%) */
 	return sq1000_brightness < ((uint) threshold) * ((uint) threshold) * 1000 ? TC_WHITE : TC_BLACK;
 }
+
+/**
+ * Lookup table of colour shades for all 16 colour gradients.
+ * 8 colours per gradient from darkest (0) to lightest (7)
+ */
+struct ColourGradients
+{
+	using ColourGradient = std::array<byte, SHADE_END>;
+
+	static inline std::array<ColourGradient, COLOUR_END> gradient{};
+};
+
+/**
+ * Get colour gradient palette index.
+ * @param colour Colour.
+ * @param shade Shade level from 1 to 7.
+ * @returns palette index of colour.
+ */
+byte GetColourGradient(Colours colour, ColourShade shade)
+{
+	return ColourGradients::gradient[colour % COLOUR_END][shade % SHADE_END];
+}
+
+/**
+ * Set colour gradient palette index.
+ * @param colour Colour.
+ * @param shade Shade level from 1 to 7.
+ * @param palette_index Palette index to set.
+ */
+void SetColourGradient(Colours colour, ColourShade shade, byte palette_index)
+{
+	assert(colour < COLOUR_END);
+	assert(shade < SHADE_END);
+	ColourGradients::gradient[colour % COLOUR_END][shade % SHADE_END] = palette_index;
+}