Add bestContrast function

Author: Perlkonig

src/renderers/_base.ts

@@ -9386,6 +9386,12 @@ export abstract class RendererBase {
                     const base = hex2rgb(this.resolveColour(val.colour) as string);
                     colour = rgb2hex(lighten(base, val.ds, val.dl));
                 }
+                // bestContrast
+                else if (val.func === "bestContrast") {
+                    const bg = this.resolveColour(val.bg) as string;
+                    const fg = val.fg.map(c => this.resolveColour(c) as string);
+                    return tinycolor.mostReadable(bg, fg).toHexString();
+                }
             }
         } else if (typeof val === "number") {
             colour = this.options.colours[val - 1];

src/schemas/schema.d.ts

@@ -12,7 +12,7 @@ export type Colourstrings = string;
 /**
  * Colours can also be derived using various functions.
  */
-export type Colourfuncs = FunctionFlatten | FunctionLighten;
+export type Colourfuncs = FunctionFlatten | FunctionBestContrast | FunctionLighten;
 export type PositiveInteger = number;
 /**
  * Schema for the `matrix` part of a polyomino-related feature
@@ -284,6 +284,14 @@ export interface FunctionFlatten {
   bg: PositiveInteger | Colourstrings;
   opacity: number;
 }
+/**
+ * Chooses the foreground colour with the best contrast against the given background.
+ */
+export interface FunctionBestContrast {
+  func: "bestContrast";
+  bg: PositiveInteger | Colourstrings;
+  fg: (PositiveInteger | Colourstrings)[];
+}
 /**
  * Lightens or darkens a colour by the specified amount of saturation and luminance. Positive deltas lighten, negative darken.
  */

src/schemas/schema.json

@@ -86,10 +86,37 @@
             "required": ["func", "colour", "ds", "dl"],
             "additionalProperties": false
         },
-        "colourfuncs": {
+        "functionBestContrast": {
+            "description": "Chooses the foreground colour with the best contrast against the given background.",
+            "type": "object",
+            "properties": {
+                "func": {
+                    "enum": ["bestContrast"]
+                },
+                "bg": {
+                    "anyOf": [
+                        {"$ref": "#/$defs/positiveInteger"},
+                        {"$ref": "#/$defs/colourstrings"}
+                    ]
+                },
+                "fg": {
+                    "type": "array",
+                    "items": {
+                        "anyOf": [
+                            {"$ref": "#/$defs/positiveInteger"},
+                            {"$ref": "#/$defs/colourstrings"}
+                        ]
+                    }
+                }
+            },
+            "required": ["func", "bg", "fg"],
+            "additionalProperties": false
+        },
+       "colourfuncs": {
             "description": "Colours can also be derived using various functions.",
             "anyOf": [
                 {"$ref": "#/$defs/functionFlatten"},
+                {"$ref": "#/$defs/functionBestContrast"},
                 {"$ref": "#/$defs/functionLighten"}
             ]
         },