fix(mode): restore indexed pixels after clearing transparency (#3080) (#3153)

crates/engine/src/mode_cmds.rs

@@ -325,11 +325,23 @@ fn color_table(s: &mut Session, p: &Value) -> Result<Value> {
             let mut data = surf.read_region(r);
             for q in data.chunks_exact_mut(n) {
                 let c = photocraft_raster::to_rgba(&fmt, q);
-                if c[3] <= 0.0 {
-                    continue;
-                }
-                let i = old.nearest([c[0], c[1], c[2]]);
-                let alpha = if table.transparent == Some(i as u8) { 0.0 } else { c[3] };
+                let rgb = [c[0], c[1], c[2]];
+                let i = if c[3] <= 0.0 {
+                    let Some(i) = old.transparent.map(usize::from) else { continue };
+                    if i >= old.colors.len() || old.rgb(i) != rgb {
+                        continue;
+                    }
+                    i
+                } else {
+                    old.nearest(rgb)
+                };
+                let alpha = if table.transparent == Some(i as u8) {
+                    0.0
+                } else if c[3] <= 0.0 {
+                    1.0
+                } else {
+                    c[3]
+                };
                 let nc = if i < table.colors.len() { table.rgb(i) } else { table.rgb(table.nearest([c[0], c[1], c[2]])) };
                 let mut enc = [0.0f32; 8];
                 let m = photocraft_raster::from_rgba_into(&fmt, [nc[0], nc[1], nc[2], alpha], &mut enc);

crates/engine/src/mode_cmds/tests.rs

@@ -192,6 +192,35 @@ fn color_table_presets_and_entries() {
     assert!(s.execute("image.mode.colorTable", json!({"entries": {"999": "#000000"}})).is_err());
 }
 
+#[test]
+fn clearing_color_table_transparency_restores_indexed_pixels() {
+    let pixel = |s: &mut Session| -> [f32; 4] { serde_json::from_value(s.execute("document.pixel", json!({"x": 5, "y": 8})).unwrap()).unwrap() };
+    let mut s = Session::new();
+    s.execute("file.new", json!({"width": 16, "height": 16, "background": "#ff0000"})).unwrap();
+    s.execute("image.mode.indexedColor", json!({"palette": "exact", "colors": 2, "forced": "none", "dither": "none"})).unwrap();
+    assert_eq!(doc(&s).color_table.as_ref().unwrap().colors, vec![[255, 0, 0]]);
+    assert_eq!(pixel(&mut s), [1.0, 0.0, 0.0, 1.0]);
+
+    s.execute("image.mode.colorTable", json!({"transparent": 0})).unwrap();
+    assert_eq!(pixel(&mut s), [0.0; 4]);
+    s.execute("image.mode.colorTable", json!({"transparent": null})).unwrap();
+    assert_eq!(doc(&s).layers[0].surface().unwrap().rgba(5, 8), [1.0, 0.0, 0.0, 1.0], "clearing the transparent palette entry should restore the stored pixel");
+    assert_eq!(pixel(&mut s), [1.0, 0.0, 0.0, 1.0]);
+    s.execute("image.mode.rgb", json!({})).unwrap();
+    assert_eq!(pixel(&mut s), [1.0, 0.0, 0.0, 1.0]);
+
+    let mut control = Session::new();
+    control.execute("file.new", json!({"width": 16, "height": 16, "background": "#ff0000"})).unwrap();
+    control.execute("image.mode.indexedColor", json!({"palette": "exact", "colors": 2, "forced": "none", "dither": "none"})).unwrap();
+    control.execute("image.mode.colorTable", json!({"entries": {"0": "#0000ff"}})).unwrap();
+    let blue: [f32; 4] = serde_json::from_value(control.execute("document.pixel", json!({"x": 5, "y": 8})).unwrap()).unwrap();
+    assert_eq!(blue, [0.0, 0.0, 1.0, 1.0]);
+    control.execute("image.mode.colorTable", json!({"transparent": 0})).unwrap();
+    control.execute("edit.undo", json!({})).unwrap();
+    let restored: [f32; 4] = serde_json::from_value(control.execute("document.pixel", json!({"x": 5, "y": 8})).unwrap()).unwrap();
+    assert_eq!(restored, [0.0, 0.0, 1.0, 1.0]);
+}
+
 #[test]
 fn bitmap_methods_need_grayscale() {
     let mut s = session(32, 32, 16, "rgb");