Fix alpha blending formula (#594)

Since `srgb_to_linear` is non-linear we can't use it for premultiplied
colors. Instead of unpremultiplying them, I changed the rest of the app
to straight alpha and introduced types to ensure we don't mess it up.

Author: lhecker

benches/lib.rs

@@ -127,9 +127,14 @@ fn bench_hash(c: &mut Criterion) {
 
 fn bench_oklab(c: &mut Criterion) {
     c.benchmark_group("oklab")
-        .bench_function("srgb_to_oklab", |b| b.iter(|| oklab::srgb_to_oklab(black_box(0xff212cbe))))
-        .bench_function("oklab_blend", |b| {
-            b.iter(|| oklab::oklab_blend(black_box(0x7f212cbe), black_box(0x7f3aae3f)))
+        .bench_function("StraightRgba::as_oklab", |b| {
+            b.iter(|| black_box(oklab::StraightRgba::from_le(0xff212cbe)).as_oklab())
+        })
+        .bench_function("StraightRgba::oklab_blend", |b| {
+            b.iter(|| {
+                black_box(oklab::StraightRgba::from_le(0x7f212cbe))
+                    .oklab_blend(black_box(oklab::StraightRgba::from_le(0x7f3aae3f)))
+            })
         });
 }
 

src/bin/edit/main.rs

@@ -26,7 +26,7 @@ use edit::arena::{self, Arena, ArenaString, scratch_arena};
 use edit::framebuffer::{self, IndexedColor};
 use edit::helpers::{CoordType, KIBI, MEBI, MetricFormatter, Rect, Size};
 use edit::input::{self, kbmod, vk};
-use edit::oklab::oklab_blend;
+use edit::oklab::StraightRgba;
 use edit::tui::*;
 use edit::vt::{self, Token};
 use edit::{apperr, arena_format, base64, path, sys, unicode};
@@ -83,15 +83,15 @@ fn run() -> apperr::Result<()> {
 
     let _restore = setup_terminal(&mut tui, &mut state, &mut vt_parser);
 
-    state.menubar_color_bg = oklab_blend(
-        tui.indexed(IndexedColor::Background),
-        tui.indexed_alpha(IndexedColor::BrightBlue, 1, 2),
-    );
+    state.menubar_color_bg = tui.indexed(IndexedColor::Background).oklab_blend(tui.indexed_alpha(
+        IndexedColor::BrightBlue,
+        1,
+        2,
+    ));
     state.menubar_color_fg = tui.contrasted(state.menubar_color_bg);
-    let floater_bg = oklab_blend(
-        tui.indexed_alpha(IndexedColor::Background, 2, 3),
-        tui.indexed_alpha(IndexedColor::Foreground, 1, 3),
-    );
+    let floater_bg = tui
+        .indexed_alpha(IndexedColor::Background, 2, 3)
+        .oklab_blend(tui.indexed_alpha(IndexedColor::Foreground, 1, 3));
     let floater_fg = tui.contrasted(floater_bg);
     tui.setup_modifier_translations(ModifierTranslations {
         ctrl: loc(LocId::Ctrl),
@@ -630,7 +630,7 @@ fn setup_terminal(tui: &mut Tui, state: &mut State, vt_parser: &mut vt::Parser)
                         }
                     }
 
-                    *color = rgb | 0xff000000;
+                    *color = StraightRgba::from_le(rgb | 0xff000000);
                     color_responses += 1;
                     osc_buffer.clear();
                 }

src/bin/edit/state.rs

@@ -8,6 +8,7 @@ use std::path::{Path, PathBuf};
 
 use edit::framebuffer::IndexedColor;
 use edit::helpers::*;
+use edit::oklab::StraightRgba;
 use edit::tui::*;
 use edit::{apperr, buffer, icu, sys};
 
@@ -127,8 +128,8 @@ pub struct OscTitleFileStatus {
 }
 
 pub struct State {
-    pub menubar_color_bg: u32,
-    pub menubar_color_fg: u32,
+    pub menubar_color_bg: StraightRgba,
+    pub menubar_color_fg: StraightRgba,
 
     pub documents: DocumentManager,
 
@@ -176,8 +177,8 @@ pub struct State {
 impl State {
     pub fn new() -> apperr::Result<Self> {
         Ok(Self {
-            menubar_color_bg: 0,
-            menubar_color_fg: 0,
+            menubar_color_bg: StraightRgba::zero(),
+            menubar_color_fg: StraightRgba::zero(),
 
             documents: Default::default(),
 

src/buffer/mod.rs

@@ -42,7 +42,7 @@ use crate::clipboard::Clipboard;
 use crate::document::{ReadableDocument, WriteableDocument};
 use crate::framebuffer::{Framebuffer, IndexedColor};
 use crate::helpers::*;
-use crate::oklab::oklab_blend;
+use crate::oklab::StraightRgba;
 use crate::simd::memchr2;
 use crate::unicode::{self, Cursor, MeasurementConfig, Utf8Chars};
 use crate::{apperr, icu, simd};
@@ -1834,12 +1834,13 @@ impl TextBuffer {
                     bottom: top + 1,
                 };
 
-                let mut bg = oklab_blend(
-                    fb.indexed(IndexedColor::Foreground),
-                    fb.indexed_alpha(IndexedColor::BrightBlue, 1, 2),
-                );
+                let mut bg = fb.indexed(IndexedColor::Foreground).oklab_blend(fb.indexed_alpha(
+                    IndexedColor::BrightBlue,
+                    1,
+                    2,
+                ));
                 if !focused {
-                    bg = oklab_blend(bg, fb.indexed_alpha(IndexedColor::Background, 1, 2))
+                    bg = bg.oklab_blend(fb.indexed_alpha(IndexedColor::Background, 1, 2));
                 };
                 let fg = fb.contrasted(bg);
                 fb.blend_bg(rect, bg);
@@ -1975,7 +1976,7 @@ impl TextBuffer {
                 right: destination.left + self.margin_width,
                 bottom: destination.bottom,
             };
-            fb.blend_fg(margin, 0x7f3f3f3f);
+            fb.blend_fg(margin, StraightRgba::from_le(0x7f7f7f7f));
         }
 
         if self.ruler > 0 {
@@ -2023,7 +2024,7 @@ impl TextBuffer {
                             right: destination.right,
                             bottom: cursor.y + 1,
                         },
-                        0x50282828,
+                        StraightRgba::from_le(0x7f7f7f7f),
                     );
                 }
             }