🐛 Fix caret not mimicking text color (#10866)

frontend/src/app/render_wasm/api.cljs

@@ -440,6 +440,8 @@
           (when (= ev TEXT_EDITOR_EVENT_STYLES_CHANGED)
             (let [current-styles (text-editor/text-editor-get-current-styles)
                   shape-id (text-editor/text-editor-get-active-shape-id)]
+              ;; Keep the caret color matching the text at the caret position.
+              (text-editor/text-editor-apply-caret-color (:fills current-styles))
               (st/emit! (texts/v3-update-text-editor-styles shape-id current-styles))))
           (recur (or needs-render?
                      (= ev TEXT_EDITOR_EVENT_CONTENT_CHANGED)
@@ -531,9 +533,13 @@
              (not (render-pending?)))
     (when (is-text-editor-wasm-enabled @st/state)
       (text-editor/text-editor-update-blink (js/performance.now))
-      (text-editor/text-editor-render-caret)
-      (when (drain-text-editor-events!)
-        (request-render-preserving-target "text-editor-content")))))
+      ;; Drain before painting so the caret color (updated on StylesChanged when
+      ;; the caret crosses into differently-colored text) is applied before the
+      ;; overlay is drawn, instead of lagging a frame behind.
+      (let [needs-render? (drain-text-editor-events!)]
+        (text-editor/text-editor-render-caret)
+        (when needs-render?
+          (request-render-preserving-target "text-editor-content"))))))
 
 ;; CSS-pixel blur radius for the page-transition snapshot (DPR-scaled in WASM).
 (def ^:private TRANSITION_BLUR_RADIUS 4.0)

frontend/src/app/render_wasm/text_editor.cljs

@@ -128,7 +128,6 @@
       nil)))
 
 (def ^:private selection-color-css-var "--text-editor-selection-background-color")
-(def ^:private caret-color-css-var "--text-editor-caret-color")
 
 (defn- resolve-theme-color
   "Resolve a themed CSS color variable (read from the document body) into a
@@ -140,17 +139,54 @@
               (dom/get-css-variable css-var js/document.body))]
     (sr-clr/hex->u32argb color opacity)))
 
+;; ARGB u32 for opaque white, painted with a Difference blend mode so the caret
+;; always shows the inverted color of the background.
+(def ^:private caret-invert-color 0xffffffff)
+
 (defn text-editor-apply-theme
-  "Push the current theme's selection and caret colors (read from the CSS
-   custom properties on the document body) into the WASM text editor. The
-   editor theme is a persistent singleton, so call once after init and again
-   on every color-scheme change."
+  "Push the current theme's selection color (read from the CSS custom properties
+   on the document body) into the WASM text editor, together with the default
+   caret: white with invert, so it shows the inverted color of the background.
+   The caret only switches to a solid text color (invert off) via
+   `text-editor-apply-caret-color`. The editor theme is a persistent singleton,
+   so call once after init and again on every color-scheme change."
   []
+  (when wasm/context-initialized?
+    (let [selection (resolve-theme-color selection-color-css-var)]
+      (when selection
+        (h/call wasm/internal-module "_text_editor_apply_theme" selection caret-invert-color true)))))
+
+(defn- solid-fill?
+  [fill]
+  (some? (:fill-color fill)))
+
+(defn resolve-caret-color
+  "Compute the caret color from the text `fills` at the caret (as returned by
+   `text-editor-get-current-styles`), as `{:color <argb-u32> :invert? bool}`:
+
+   - when there is at least one solid fill, match the topmost (visible) one,
+     painted normally (`:invert? false`);
+   - otherwise (no fill, gradient, image fills, mixed selection, …) use white
+     with `:invert? true`, which the renderer paints with a Difference blend so
+     the caret is the inverted color of whatever is behind it."
+  [fills]
+  (if-let [solid (and (sequential? fills)
+                      (some #(when (solid-fill? %) %) fills))]
+    {:color (sr-clr/hex->u32argb (:fill-color solid) (:fill-opacity solid))
+     :invert? false}
+    {:color caret-invert-color
+     :invert? true}))
+
+(defn text-editor-apply-caret-color
+  "Update the WASM text-editor caret color so it matches the text at the caret
+   (see `resolve-caret-color`). Re-applies the current theme selection color
+   unchanged, since the WASM theme is a singleton holding both."
+  [fills]
   (when wasm/context-initialized?
     (let [selection (resolve-theme-color selection-color-css-var)
-          caret     (resolve-theme-color caret-color-css-var)]
-      (when (and selection caret)
-        (h/call wasm/internal-module "_text_editor_apply_theme" selection caret)))))
+          {:keys [color invert?]} (resolve-caret-color fills)]
+      (when selection
+        (h/call wasm/internal-module "_text_editor_apply_theme" selection color invert?)))))
 
 (defn text-editor-focus
   [id]

frontend/test/frontend_tests/render_wasm/text_editor_caret_color_test.cljs

@@ -0,0 +1,67 @@
+;; This Source Code Form is subject to the terms of the Mozilla Public
+;; License, v. 2.0. If a copy of the MPL was not distributed with this
+;; file, You can obtain one at http://mozilla.org/MPL/2.0/.
+;;
+;; Copyright (c) KALEIDOS INC Sucursal en España SL
+
+(ns frontend-tests.render-wasm.text-editor-caret-color-test
+  "Unit tests for the text-editor caret color resolution.
+
+   The caret matches the topmost solid fill of the text at the caret. For
+   anything else (no fill, gradient, image fills, mixed selection) it falls back
+   to an inverted caret (white painted with a Difference blend)."
+  (:require
+   [app.render-wasm.serializers.color :as sr-clr]
+   [app.render-wasm.text-editor :as text-editor]
+   [cljs.test :as t :include-macros true]))
+
+(def ^:private white 0xffffffff)
+
+(defn- solid [color opacity]
+  {:fill-color color :fill-opacity opacity})
+
+(defn- gradient [stops]
+  {:fill-color-gradient {:type :linear :stops stops}})
+
+(t/deftest resolve-caret-color-solid
+  (t/testing "a single solid fill is matched, painted normally"
+    (t/is (= {:color (sr-clr/hex->u32argb "#ff0000" 1) :invert? false}
+             (text-editor/resolve-caret-color [(solid "#ff0000" 1)]))))
+
+  (t/testing "the topmost (first, visible) solid fill wins over the ones below"
+    (t/is (= {:color (sr-clr/hex->u32argb "#ff0000" 1) :invert? false}
+             (text-editor/resolve-caret-color [(solid "#ff0000" 1) (solid "#00ff00" 1)]))))
+
+  (t/testing "the solid fill opacity is preserved"
+    (t/is (= {:color (sr-clr/hex->u32argb "#00ff00" 0.5) :invert? false}
+             (text-editor/resolve-caret-color [{:fill-image {:id "x"}} (solid "#00ff00" 0.5)]))))
+
+  (t/testing "a solid fill takes precedence over a gradient"
+    (t/is (= {:color (sr-clr/hex->u32argb "#ff0000" 1) :invert? false}
+             (text-editor/resolve-caret-color
+              [(solid "#ff0000" 1)
+               (gradient [{:color "#000000" :opacity 1 :offset 0}
+                          {:color "#ffffff" :opacity 1 :offset 1}])])))))
+
+(t/deftest resolve-caret-color-inverted
+  (t/testing "a gradient falls back to the inverted caret"
+    (t/is (= {:color white :invert? true}
+             (text-editor/resolve-caret-color
+              [(gradient [{:color "#ff0000" :opacity 1 :offset 0}
+                          {:color "#0000ff" :opacity 1 :offset 1}])]))))
+
+  (t/testing "an image-only fill falls back to the inverted caret"
+    (t/is (= {:color white :invert? true}
+             (text-editor/resolve-caret-color [{:fill-image {:id "x"}}]))))
+
+  (t/testing "no fills fall back to the inverted caret"
+    (t/is (= {:color white :invert? true}
+             (text-editor/resolve-caret-color []))))
+
+  (t/testing "nil falls back to the inverted caret"
+    (t/is (= {:color white :invert? true}
+             (text-editor/resolve-caret-color nil))))
+
+  (t/testing "a mixed selection (:multiple) falls back to the inverted caret"
+    (t/is (= {:color white :invert? true}
+             (text-editor/resolve-caret-color :multiple)))))

frontend/test/frontend_tests/runner.cljs

@@ -49,6 +49,7 @@
    [frontend-tests.plugins.utils-test]
    [frontend-tests.plugins.value-objects-test]
    [frontend-tests.render-wasm.process-objects-test]
+   [frontend-tests.render-wasm.text-editor-caret-color-test]
    [frontend-tests.svg-fills-test]
    [frontend-tests.text-editor-paste-guard-test]
    [frontend-tests.tokens.copy-paste-props-test]
@@ -136,6 +137,7 @@
    'frontend-tests.plugins.utils-test
    'frontend-tests.plugins.value-objects-test
    'frontend-tests.render-wasm.process-objects-test
+   'frontend-tests.render-wasm.text-editor-caret-color-test
    'frontend-tests.svg-fills-test
    'frontend-tests.tokens.copy-paste-props-test
    'frontend-tests.tokens.import-export-test

render-wasm/src/render/text_editor.rs

@@ -66,6 +66,11 @@ fn render_cursor(
     if editor_state.is_overtype_mode {
         paint.set_blend_mode(BlendMode::Exclusion);
         paint.set_color(Color::WHITE);
+    } else if editor_state.theme.cursor_invert {
+        // Default (no solid fill to match): a white caret with a Difference
+        // blend renders the inverted color of whatever is behind it.
+        paint.set_blend_mode(BlendMode::Difference);
+        paint.set_color(editor_state.theme.cursor_color);
     } else {
         paint.set_blend_mode(BlendMode::SrcOver);
         paint.set_color(editor_state.theme.cursor_color);

render-wasm/src/state/text_editor.rs

@@ -101,7 +101,7 @@ pub enum TextEditorEvent {
 
 /// FIXME: It should be better to get these constants from the frontend through the API.
 const SELECTION_COLOR: Color = Color::from_argb(127, 0, 209, 184);
-const CURSOR_COLOR: Color = Color::BLACK;
+const CURSOR_COLOR: Color = Color::WHITE;
 const CURSOR_WIDTH: f32 = 1.0;
 const CURSOR_BLINK_INTERVAL_MS: f32 = 530.0;
 
@@ -274,6 +274,10 @@ pub struct TextEditorTheme {
     pub selection_color: Color,
     pub cursor_color: Color,
     pub cursor_width: f32,
+    /// When true the caret is painted with a Difference blend mode, so it shows
+    /// as the inverted color of whatever is behind it. Used as the default when
+    /// the text has no solid fill whose color the caret can match.
+    pub cursor_invert: bool,
 }
 
 pub struct TextComposition {
@@ -364,6 +368,7 @@ impl TextEditorState {
                 selection_color: SELECTION_COLOR,
                 cursor_color: CURSOR_COLOR,
                 cursor_width: CURSOR_WIDTH,
+                cursor_invert: true,
             },
             selection: TextSelection::new(),
             composition: TextComposition::new(),

render-wasm/src/wasm/text_editor.rs

@@ -33,12 +33,17 @@ pub enum CursorDirection {
 // STATE MANAGEMENT
 // ============================================================================
 
+/// Apply the editor theme. When `invert` is true the caret is painted with a
+/// Difference blend mode (pass white as `cursor_color` to always show the
+/// inverted color of the background); otherwise it is painted with the given
+/// solid `cursor_color`.
 #[no_mangle]
-pub extern "C" fn text_editor_apply_theme(selection_color: u32, cursor_color: u32) {
+pub extern "C" fn text_editor_apply_theme(selection_color: u32, cursor_color: u32, invert: bool) {
     // NOTE: In the future could be interesting to fill al this data from
     // a structure pointer.
     get_text_editor_state().theme.selection_color = Color::new(selection_color);
     get_text_editor_state().theme.cursor_color = Color::new(cursor_color);
+    get_text_editor_state().theme.cursor_invert = invert;
 }
 
 #[no_mangle]