Implementation of https://github.com/nesbox/TIC-80/wiki/code-examples-and-snippets#rainbow-color-function in Zig ⚡

rainbow.zig

const tic = @import("tic80.zig");

const Rainbow = struct {
    red: u8 = 255,
    grn: u8 = 0,
    blu: u8 = 0,
    cyRG: bool = true,
    cyGB: bool = false,
    cyBR: bool = false,

    fn update(self: *Rainbow, slot: u32) void {
        if (self.cyRG == true) {
            self.grn +|= 1;
            if (self.grn == 255) {
                self.red -|= 1;
            }

            if (self.red == 0) {
                self.cyRG = false;
                self.cyGB = true;
            }
        }

        if (self.cyGB == true) {
            self.blu +|= 1;
            if (self.blu == 255) {
                self.grn -|= 1;

                if (self.grn == 0) {
                    self.cyGB = false;
                    self.cyBR = true;
                }
            }
        }

        if (self.cyBR == true) {
            self.red +|= 1;

            if (self.red == 255) {
                self.blu -|= 1;

                if (self.blu == 0) {
                    self.cyBR = false;
                    self.cyRG = true;
                }
            }
        }

        tic.poke(0x3fc0 + (slot * 3) + 2, self.blu);
        tic.poke(0x3fc0 + (slot * 3) + 1, self.grn);
        tic.poke(0x3fc0 + (slot * 3), self.red);
    }
};

Updating the color in BDR:

Updating the color in TIC: