1 files changed, 20 insertions, 0 deletions
diff --git a/src/draw.zig b/src/draw.zig
index 93d5b2d9..b0b16e12 100644
--- a/src/draw.zig
+++ b/src/draw.zig
@@ -723,6 +723,7 @@ fn composedCell(
     return switch (animation.charSource(track, col - area.x0, row - area.y0, area)) {
         .old => canonical.previous_cells[index],
         .byte => |byte| withByte(canonical.cells[index], byte),
+        .edge => |weight| towardGround(canonical.cells[index], canonical.previous_cells[index].style.bg, weight),
         // Churn belongs on the glyph, not on the pane's empty space, and it
         // borrows whichever side of the diff actually has one.
         .churn => |byte| blk: {
@@ -749,6 +750,25 @@ fn composedCell(
     };
 }
 
+/// A cell with its ink and ground drawn `weight` of the way toward another
+/// ground, in OKLab. A palette or default colour cannot be mixed, so the
+/// ground steps over at the halfway point instead.
+fn towardGround(cell: Cell, ground: Color, weight: f32) Cell {
+    var out = cell;
+    const to = switch (ground) {
+        .rgb => |rgb| rgb,
+        .default, .index => return if (weight >= 0.5) blk: {
+            out.style.bg = ground;
+            break :blk out;
+        } else out,
+    };
+    inline for (.{ &out.style.fg, &out.style.bg }) |color| switch (color.*) {
+        .rgb => |rgb| color.* = .{ .rgb = colors.mixOklab(rgb, to, weight) },
+        .default, .index => {},
+    };
+    return out;
+}
+
 fn withByte(cell: Cell, byte: u8) Cell {
     var out = cell;
     out.text[0] = byte;