colour emulation

Cargo.lock

@@ -992,6 +992,7 @@ dependencies = [
  "bytemuck",
  "futures",
  "itertools",
+ "num-traits",
  "once_cell",
  "rand",
  "serde",

lib/Cargo.toml

@@ -16,3 +16,4 @@ itertools = "0.10.5"
 serde = { version = "1.0", features = ["derive"] }
 serde_with = "2.3.1"
 bytemuck = "1.13"
+num-traits = "0.2"

lib/src/processor/memory/mmio/gpu/types.rs

@@ -3,7 +3,7 @@ use serde::{Deserialize, Serialize};
 
 use crate::{
     processor::memory::addresses::{OamAddress, VramAddress},
-    util::{as_signed, get_bit},
+    util::{as_signed, get_bit, SaturatingCast},
 };
 
 use super::cgb::CgbPalette;
@@ -117,10 +117,24 @@ impl From<Colour> for [u8; 4] {
 }
 
 fn rgb_from_bytes(bytes: u16) -> Colour {
-    let blue = (((bytes & (0b11111 << 10)) >> 10) << 3) as u8;
+    let b = (bytes & (0b11111 << 10)) >> 10;
-    let green = (((bytes & (0b11111 << 5)) >> 5) << 3) as u8;
+    let g = (bytes & (0b11111 << 5)) >> 5;
-    let red = ((bytes & 0b11111) << 3) as u8;
+    let r = bytes & 0b11111;
-    Colour(red, green, blue)
+    // direct colour emulation:
+    // let blue = (raw_blue << 3) | (raw_blue >> 2);
+    // let green = (raw_green << 3) | (raw_green >> 2);
+    // let red = (raw_red << 3) | (raw_red >> 2);
+
+    // colour emulation from
+    // https://web.archive.org/web/20200322151952/https://byuu.net/video/color-emulation
+    let blue = (r * 6 + g * 4 + b * 22).min(960) >> 2;
+    let green = (g * 24 + b * 8).min(960) >> 2;
+    let red = (r * 26 + g * 4 + b * 2).min(960) >> 2;
+    Colour(
+        red.saturating_cast(),
+        green.saturating_cast(),
+        blue.saturating_cast(),
+    )
 }
 
 impl ColourInner {

lib/src/util.rs

@@ -1,3 +1,5 @@
+use num_traits::{PrimInt, Unsigned};
+
 use crate::processor::{memory::mmio::gpu::Colour, Direction};
 use std::{io, mem::transmute};
 
@@ -82,6 +84,23 @@ impl Nibbles for u8 {
     }
 }
 
+pub trait SaturatingCast<T>
+where
+    T: PrimInt + Unsigned,
+{
+    fn saturating_cast(&self) -> T;
+}
+
+impl<F, T> SaturatingCast<T> for F
+where
+    T: PrimInt + Unsigned + TryFrom<F>,
+    F: PrimInt + Unsigned,
+{
+    fn saturating_cast(&self) -> T {
+        (*self).try_into().unwrap_or(T::max_value())
+    }
+}
+
 pub fn scale_buffer<T: From<Colour> + Copy>(
     buffer: &[T],
     width: usize,