ST77xx LCD driver (#926)

ST7735 and ST7789 driver implementation. Tested against [Pico LCD
0.96](https://www.waveshare.com/wiki/Pico-LCD-0.96) [ST7735] and [Pico
LCD 1.3](https://www.waveshare.com/wiki/Pico-LCD-1.3) [ST7789]

---------

Co-authored-by: Arkadiusz Wójcik <wojcik.arkadiusz@outlook.com>

Author: arkadiuszwojcik

drivers/display/colors.zig

@@ -1,40 +1,38 @@
 //!
 //! This file provides common color types found on the supported displays.
 //!
+//!
+const std = @import("std");
 
 /// A color type encoding only black and white.
 pub const BlackWhite = enum(u1) {
     black = 0,
     white = 1,
 };
 
-pub const RGB565 = Color(.{ u5, u6, u5 });
-pub const RGB888 = Color(.{ u8, u8, u8 });
-
-/// Provides a namespace with the default colors for the given `Color` type.
-pub fn Color(comptime Ts: [3]type) type {
-    return packed struct {
+pub fn RGB565_Generic(desired_endianness: std.builtin.Endian) type {
+    return struct {
         const Self = @This();
 
-        r: Ts[0],
-        g: Ts[1],
-        b: Ts[2],
+        value: u16,
 
-        pub const black: Self = .from_rgb(0x00, 0x00, 0x00);
-        pub const white: Self = .from_rgb(0xFF, 0xFF, 0xFF);
-        pub const red: Self = .from_rgb(0xFF, 0x00, 0x00);
-        pub const green: Self = .from_rgb(0x00, 0xFF, 0x00);
-        pub const blue: Self = .from_rgb(0x00, 0x00, 0xFF);
-        pub const cyan: Self = .from_rgb(0x00, 0xFF, 0xFF);
-        pub const magenta: Self = .from_rgb(0xFF, 0x00, 0xFF);
-        pub const yellow: Self = .from_rgb(0xFF, 0xFF, 0x00);
+        pub const black: Self = from_rgb(0x00, 0x00, 0x00);
+        pub const white: Self = from_rgb(0xFF, 0xFF, 0xFF);
+        pub const red: Self = from_rgb(0xFF, 0x00, 0x00);
+        pub const green: Self = from_rgb(0x00, 0xFF, 0x00);
+        pub const blue: Self = from_rgb(0x00, 0x00, 0xFF);
+        pub const cyan: Self = from_rgb(0x00, 0xFF, 0xFF);
+        pub const magenta: Self = from_rgb(0xFF, 0x00, 0xFF);
+        pub const yellow: Self = from_rgb(0xFF, 0xFF, 0x00);
 
         pub fn from_rgb(r: u8, g: u8, b: u8) Self {
-            return Self{
-                .r = @truncate(r >> (8 - @bitSizeOf(Ts[0]))),
-                .g = @truncate(g >> (8 - @bitSizeOf(Ts[1]))),
-                .b = @truncate(b >> (8 - @bitSizeOf(Ts[2]))),
-            };
+            const r5: u16 = @as(u16, r) >> 3;
+            const g6: u16 = @as(u16, g) >> 2;
+            const b5: u16 = @as(u16, b) >> 3;
+
+            const v: u16 = (r5 << 11) | (g6 << 5) | b5;
+
+            return .{ .value = std.mem.nativeTo(u16, v, desired_endianness) };
         }
     };
 }