Adds a color matrix layer to GAGS (tgstation#63957)

* Adds a color matrix layer to GAGS

* Fixes default row value

* Passes along the last viable icon for color matrix use

* Removes stray nocache reference

code/datums/greyscale/_greyscale_config.dm

@@ -231,20 +231,20 @@
 	fcopy(icon_output, "tmp/gags_debug_output.dmi")
 
 /// Actually create the icon and color it in, handles caching
-/datum/greyscale_config/proc/Generate(color_string)
+/datum/greyscale_config/proc/Generate(color_string, icon/last_external_icon)
 	var/key = color_string
 	var/icon/new_icon = icon_cache[key]
 	if(new_icon)
 		return icon(new_icon)
 
-	var/icon/icon_bundle = GenerateBundle(color_string)
+	var/icon/icon_bundle = GenerateBundle(color_string, last_external_icon=last_external_icon)
 	icon_bundle = fcopy_rsc(icon_bundle)
 	icon_cache[key] = icon_bundle
 	var/icon/output = icon(icon_bundle)
 	return output
 
 /// Handles the actual icon manipulation to create the spritesheet
-/datum/greyscale_config/proc/GenerateBundle(list/colors, list/render_steps)
+/datum/greyscale_config/proc/GenerateBundle(list/colors, list/render_steps, icon/last_external_icon)
 	if(!istype(colors))
 		colors = SSgreyscale.ParseColorString(colors)
 	if(length(colors) != expected_colors)
@@ -255,7 +255,7 @@
 		var/list/icon_state_steps
 		if(render_steps)
 			icon_state_steps = render_steps[icon_state] = list()
-		var/icon/generated_icon = GenerateLayerGroup(colors, icon_states[icon_state], icon_state_steps)
+		var/icon/generated_icon = GenerateLayerGroup(colors, icon_states[icon_state], icon_state_steps, last_external_icon)
 		// We read a pixel to force the icon to be fully generated before we let it loose into the world
 		// I hate this
 		generated_icon.GetPixel(1, 1)
@@ -271,15 +271,15 @@
 	return icon_bundle
 
 /// Internal recursive proc to handle nested layer groups
-/datum/greyscale_config/proc/GenerateLayerGroup(list/colors, list/group, list/render_steps)
+/datum/greyscale_config/proc/GenerateLayerGroup(list/colors, list/group, list/render_steps, icon/last_external_icon)
 	var/icon/new_icon
 	for(var/datum/greyscale_layer/layer as anything in group)
 		var/icon/layer_icon
 		if(islist(layer))
-			layer_icon = GenerateLayerGroup(colors, layer, render_steps)
+			layer_icon = GenerateLayerGroup(colors, layer, render_steps, new_icon || last_external_icon)
 			layer = layer[1] // When there are multiple layers in a group like this we use the first one's blend mode
 		else
-			layer_icon = layer.Generate(colors, render_steps)
+			layer_icon = layer.Generate(colors, render_steps, new_icon || last_external_icon)
 
 		if(!new_icon)
 			new_icon = layer_icon

code/datums/greyscale/json_reader.dm

@@ -31,6 +31,27 @@
 		new_values += new_value
 	return new_values
 
+/datum/json_reader/color_matrix/ReadJson(list/value)
+	if(!istype(value))
+		CRASH("Expected a list but got [value]")
+	if(length(value) > 5 || length(value) < 4)
+		CRASH("Color matrix must contain 4 or 5 rows")
+	var/list/new_values = list()
+	for(var/list/row in value)
+		var/list/interpreted_row = list()
+		if(!istype(row) || length(row) != 4)
+			stack_trace("Expected list to contain further row lists with exactly 4 entries")
+			interpreted_row = list(0, 0, 0, 0)
+			continue
+		for(var/number in row)
+			if(!isnum(number))
+				stack_trace("Each color matrix row must only contain numbers")
+				interpreted_row += 0
+			else
+				interpreted_row += number
+		new_values += interpreted_row
+	return new_values
+
 /datum/json_reader/blend_mode
 	var/static/list/blend_modes = list(
 		"add" = ICON_ADD,

code/datums/greyscale/layer.dm

@@ -66,18 +66,19 @@
 
 /// Used to actualy create the layer using the given colors
 /// Do not override, use InternalGenerate instead
-/datum/greyscale_layer/proc/Generate(list/colors, list/render_steps)
+/datum/greyscale_layer/proc/Generate(list/colors, list/render_steps, icon/new_icon)
 	var/list/processed_colors = list()
 	for(var/i in color_ids)
 		if(isnum(i))
 			processed_colors += colors[i]
 		else
 			processed_colors += i
-	return InternalGenerate(processed_colors, render_steps)
+	var/icon/copy_of_new_icon = icon(new_icon) // Layers shouldn't be modifying it directly, this is just for them to reference
+	return InternalGenerate(processed_colors, render_steps, copy_of_new_icon)
 
 /// Override this to implement layers.
 /// The colors var will only contain colors that this layer is configured to use.
-/datum/greyscale_layer/proc/InternalGenerate(list/colors, list/render_steps)
+/datum/greyscale_layer/proc/InternalGenerate(list/colors, list/render_steps, icon/new_icon)
 
 ////////////////////////////////////////////////////////
 // Subtypes
@@ -103,11 +104,25 @@
 	. = ..()
 	required_values[NAMEOF(src, icon_state)] = /datum/json_reader/text
 
-/datum/greyscale_layer/icon_state/InternalGenerate(list/colors, list/render_steps)
+/datum/greyscale_layer/icon_state/InternalGenerate(list/colors, list/render_steps, icon/new_icon)
 	. = ..()
-	var/icon/new_icon = icon(icon)
+	var/icon/generated_icon = icon(icon)
 	if(length(colors))
-		new_icon.Blend(colors[1], ICON_MULTIPLY)
+		generated_icon.Blend(colors[1], ICON_MULTIPLY)
+	return generated_icon
+
+/// A layer to modify the previous layer's colors with a color matrix
+/datum/greyscale_layer/color_matrix
+	layer_type = "color_matrix"
+	var/list/color_matrix
+
+/datum/greyscale_layer/color_matrix/GetExpectedValues(list/required_values, list/optional_values)
+	. = ..()
+	required_values[NAMEOF(src, color_matrix)] = /datum/json_reader/color_matrix
+
+/datum/greyscale_layer/color_matrix/InternalGenerate(list/colors, list/render_steps, icon/new_icon)
+	. = ..()
+	new_icon.MapColors(arglist(color_matrix))
 	return new_icon
 
 /// A layer created by using another greyscale icon's configuration
@@ -130,12 +145,12 @@
 	if(!reference_type.icon_states[icon_state])
 		CRASH("[src] expects icon_state '[icon_state]' but referenced configuration '[reference_type]' does not have it.")
 
-/datum/greyscale_layer/reference/InternalGenerate(list/colors, list/render_steps)
+/datum/greyscale_layer/reference/InternalGenerate(list/colors, list/render_steps, icon/new_icon)
 	var/icon/generated_icon
 	if(render_steps)
 		var/list/reference_data = list()
-		generated_icon = reference_type.GenerateBundle(colors, reference_data)
+		generated_icon = reference_type.GenerateBundle(colors, reference_data, new_icon)
 		render_steps += reference_data[icon_state]
 	else
-		generated_icon = reference_type.Generate(colors.Join())
+		generated_icon = reference_type.Generate(colors.Join(), new_icon)
 	return icon(generated_icon, icon_state)