Use browser's font size instead of hardcoded 16px as root font size (#12246)

* WIP Use browser font size instead of hardcoded 16px

* Add font migration to v3

* Remove custom font size input

* Use a dropdown instead of a slider

* Add margin to the font size dropdown

* Fix `UpdateFontSizeDelta` action typo

* Fix `fontScale`in `Call.ts`

* Rename `baseFontSizeV3` to `fontSizeDelta`

* Update playwright test

* Add `default` next to the browser font size

* Remove remaining `TODO`

* Remove falsy `private`

* Improve doc

* Update snapshots after develop merge

* Remove commented import

playwright/e2e/settings/appearance-user-settings-tab.spec.ts

@@ -73,48 +73,18 @@ test.describe("Appearance user settings tab", () => {
         await expect(page.locator(".mx_RoomView_body[data-layout='bubble']")).toBeVisible();
     });
 
-    test("should support changing font size by clicking the font slider", async ({ page, app, user }) => {
+    test("should support changing font size by using the font size dropdown", async ({ page, app, user }) => {
         await app.settings.openUserSettings("Appearance");
 
         const tab = page.getByTestId("mx_AppearanceUserSettingsTab");
-        const fontSliderSection = tab.locator(".mx_FontScalingPanel_fontSlider");
+        const fontDropdown = tab.locator(".mx_FontScalingPanel_Dropdown");
+        await expect(fontDropdown.getByLabel("Font size")).toBeVisible();
 
-        await expect(fontSliderSection.getByLabel("Font size")).toBeVisible();
+        // Default browser font size is 16px and the select value is 0
+        // -4 value is 12px
+        await fontDropdown.getByLabel("Font size").selectOption({ value: "-4" });
 
-        const slider = fontSliderSection.getByRole("slider");
+        await expect(page).toMatchScreenshot("window-12px.png");
-        // Click the left position of the slider
-        await slider.click({ position: { x: 0, y: 10 } });
-
-        const MIN_FONT_SIZE = 11;
-        // Assert that the smallest font size is selected
-        await expect(fontSliderSection.locator(`input[value='${MIN_FONT_SIZE}']`)).toBeVisible();
-        await expect(
-            fontSliderSection.locator("output .mx_Slider_selection_label", { hasText: String(MIN_FONT_SIZE) }),
-        ).toBeVisible();
-
-        await expect(fontSliderSection).toMatchScreenshot(`font-slider-${MIN_FONT_SIZE}.png`);
-
-        // Click the right position of the slider
-        await slider.click({ position: { x: 572, y: 10 } });
-
-        const MAX_FONT_SIZE = 21;
-        // Assert that the largest font size is selected
-        await expect(fontSliderSection.locator(`input[value='${MAX_FONT_SIZE}']`)).toBeVisible();
-        await expect(
-            fontSliderSection.locator("output .mx_Slider_selection_label", { hasText: String(MAX_FONT_SIZE) }),
-        ).toBeVisible();
-
-        await expect(fontSliderSection).toMatchScreenshot(`font-slider-${MAX_FONT_SIZE}.png`);
-    });
-
-    test("should disable font size slider when custom font size is used", async ({ page, app, user }) => {
-        await app.settings.openUserSettings("Appearance");
-
-        const panel = page.getByTestId("mx_FontScalingPanel");
-        await panel.locator("label", { hasText: "Use custom size" }).click();
-
-        // Assert that the font slider is disabled
-        await expect(panel.locator(".mx_FontScalingPanel_fontSlider input[disabled]")).toBeVisible();
     });
 
     test("should support enabling compact group (modern) layout", async ({ page, app, user }) => {

res/css/views/settings/_FontScalingPanel.pcss

@@ -36,26 +36,8 @@ limitations under the License.
     }
 }
 
-.mx_FontScalingPanel_fontSlider {
+.mx_FontScalingPanel_Dropdown {
-    display: flex;
+    width: 120px;
-    align-items: center;
+    /* Override default mx_Field margin */
-    padding: 15px $spacing-20 35px;
+    margin-bottom: var(--cpd-space-2x) !important;
-    background: $panels;
-    border-radius: 10px;
-    font-size: $font-10px;
-
-    .mx_FontScalingPanel_fontSlider_smallText,
-    .mx_FontScalingPanel_fontSlider_largeText {
-        font-weight: 500;
-    }
-
-    .mx_FontScalingPanel_fontSlider_smallText {
-        font-size: $font-15px;
-        padding-inline-end: $spacing-20;
-    }
-
-    .mx_FontScalingPanel_fontSlider_largeText {
-        font-size: $font-18px;
-        padding-inline-start: $spacing-20;
-    }
 }

src/components/views/settings/FontScalingPanel.tsx

@@ -14,29 +14,26 @@ See the License for the specific language governing permissions and
 limitations under the License.
 */
 
-import React, { ChangeEvent } from "react";
+import React from "react";
 
 import EventTilePreview from "../elements/EventTilePreview";
-import Field from "../elements/Field";
-import SettingsFlag from "../elements/SettingsFlag";
 import SettingsStore from "../../../settings/SettingsStore";
-import Slider from "../elements/Slider";
-import { FontWatcher } from "../../../settings/watchers/FontWatcher";
-import { IValidationResult, IFieldState } from "../elements/Validation";
 import { Layout } from "../../../settings/enums/Layout";
 import { MatrixClientPeg } from "../../../MatrixClientPeg";
 import { SettingLevel } from "../../../settings/SettingLevel";
 import { _t } from "../../../languageHandler";
-import { clamp } from "../../../utils/numbers";
 import SettingsSubsection from "./shared/SettingsSubsection";
+import Field from "../elements/Field";
+import { FontWatcher } from "../../../settings/watchers/FontWatcher";
 
 interface IProps {}
 
 interface IState {
+    browserFontSize: number;
     // String displaying the current selected fontSize.
-    // Needs to be string for things like '17.' without
+    // Needs to be string for things like '1.' without
     // trailing 0s.
-    fontSize: string;
+    fontSizeDelta: number;
     useCustomFontSize: boolean;
     layout: Layout;
     // User profile data for the message preview
@@ -47,6 +44,10 @@ interface IState {
 
 export default class FontScalingPanel extends React.Component<IProps, IState> {
     private readonly MESSAGE_PREVIEW_TEXT = _t("common|preview_message");
+    /**
+     * Font sizes available (in px)
+     */
+    private readonly sizes = [9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 20, 22, 24, 26, 28, 30, 32, 34, 36];
     private layoutWatcherRef?: string;
     private unmounted = false;
 
@@ -54,7 +55,8 @@ export default class FontScalingPanel extends React.Component<IProps, IState> {
         super(props);
 
         this.state = {
-            fontSize: SettingsStore.getValue("baseFontSizeV2", null).toString(),
+            fontSizeDelta: SettingsStore.getValue<number>("fontSizeDelta", null),
+            browserFontSize: FontWatcher.getBrowserDefaultFontSize(),
             useCustomFontSize: SettingsStore.getValue("useCustomFontSize"),
             layout: SettingsStore.getValue("layout"),
         };
@@ -90,30 +92,22 @@ export default class FontScalingPanel extends React.Component<IProps, IState> {
         }
     }
 
-    private onFontSizeChanged = (size: number): void => {
+    /**
-        this.setState({ fontSize: size.toString() });
+     * Save the new font size
-        SettingsStore.setValue("baseFontSizeV2", null, SettingLevel.DEVICE, size);
+     * @param delta
+     */
+    private onFontSizeChanged = async (delta: string): Promise<void> => {
+        const parsedDelta = parseInt(delta, 10) || 0;
+        this.setState({ fontSizeDelta: parsedDelta });
+        await SettingsStore.setValue("fontSizeDelta", null, SettingLevel.DEVICE, parsedDelta);
     };
 
-    private onValidateFontSize = async ({ value }: Pick<IFieldState, "value">): Promise<IValidationResult> => {
+    /**
-        const parsedSize = parseFloat(value!);
+     * Compute the difference between the selected font size and the browser font size
-        const min = FontWatcher.MIN_SIZE;
+     * @param fontSize
-        const max = FontWatcher.MAX_SIZE;
+     */
-
+    private computeDeltaFontSize = (fontSize: number): number => {
-        if (isNaN(parsedSize)) {
+        return fontSize - this.state.browserFontSize;
-            return { valid: false, feedback: _t("settings|appearance|font_size_nan") };
-        }
-
-        if (!(min <= parsedSize && parsedSize <= max)) {
-            return {
-                valid: false,
-                feedback: _t("settings|appearance|font_size_limit", { min, max }),
-            };
-        }
-
-        SettingsStore.setValue("baseFontSizeV2", null, SettingLevel.DEVICE, parseInt(value!, 10));
-
-        return { valid: true, feedback: _t("settings|appearance|font_size_valid", { min, max }) };
     };
 
     public render(): React.ReactNode {
@@ -123,6 +117,21 @@ export default class FontScalingPanel extends React.Component<IProps, IState> {
                 stretchContent
                 data-testid="mx_FontScalingPanel"
             >
+                <Field
+                    element="select"
+                    className="mx_FontScalingPanel_Dropdown"
+                    label={_t("settings|appearance|font_size")}
+                    value={this.state.fontSizeDelta.toString()}
+                    onChange={(e) => this.onFontSizeChanged(e.target.value)}
+                >
+                    {this.sizes.map((size) => (
+                        <option key={size} value={this.computeDeltaFontSize(size)}>
+                            {size === this.state.browserFontSize
+                                ? _t("settings|appearance|font_size_default", { fontSize: size })
+                                : size}
+                        </option>
+                    ))}
+                </Field>
                 <EventTilePreview
                     className="mx_FontScalingPanel_preview"
                     message={this.MESSAGE_PREVIEW_TEXT}
@@ -131,49 +140,6 @@ export default class FontScalingPanel extends React.Component<IProps, IState> {
                     displayName={this.state.displayName}
                     avatarUrl={this.state.avatarUrl}
                 />
-                <div className="mx_FontScalingPanel_fontSlider">
-                    <div className="mx_FontScalingPanel_fontSlider_smallText">Aa</div>
-                    <Slider
-                        min={FontWatcher.MIN_SIZE}
-                        max={FontWatcher.MAX_SIZE}
-                        step={1}
-                        value={parseInt(this.state.fontSize, 10)}
-                        onChange={this.onFontSizeChanged}
-                        displayFunc={(_) => ""}
-                        disabled={this.state.useCustomFontSize}
-                        label={_t("settings|appearance|font_size")}
-                    />
-                    <div className="mx_FontScalingPanel_fontSlider_largeText">Aa</div>
-                </div>
-
-                <SettingsFlag
-                    name="useCustomFontSize"
-                    level={SettingLevel.ACCOUNT}
-                    onChange={(checked) => {
-                        this.setState({ useCustomFontSize: checked });
-                        if (!checked) {
-                            const size = parseInt(this.state.fontSize, 10);
-                            const clamped = clamp(size, FontWatcher.MIN_SIZE, FontWatcher.MAX_SIZE);
-                            if (clamped !== size) {
-                                this.onFontSizeChanged(clamped);
-                            }
-                        }
-                    }}
-                    useCheckbox={true}
-                />
-
-                <Field
-                    type="number"
-                    label={_t("settings|appearance|font_size")}
-                    autoComplete="off"
-                    placeholder={this.state.fontSize.toString()}
-                    value={this.state.fontSize.toString()}
-                    id="font_size_field"
-                    onValidate={this.onValidateFontSize}
-                    onChange={(value: ChangeEvent<HTMLInputElement>) => this.setState({ fontSize: value.target.value })}
-                    disabled={!this.state.useCustomFontSize}
-                    className="mx_AppearanceUserSettingsTab_checkboxControlledField"
-                />
             </SettingsSubsection>
         );
     }

src/dispatcher/actions.ts

@@ -107,9 +107,11 @@ export enum Action {
     MigrateBaseFontSize = "migrate_base_font_size",
 
     /**
-     * Sets the apps root font size. Should be used with UpdateFontSizePayload
+     * Sets the apps root font size delta. Should be used with UpdateFontSizeDeltaPayload
+     * It will add the delta to the current font size.
+     * The delta should be between {@link FontWatcher.MIN_DELTA} and {@link FontWatcher.MAX_DELTA}.
      */
-    UpdateFontSize = "update_font_size",
+    UpdateFontSizeDelta = "update_font_size_delta",
 
     /**
      * Sets a system font. Should be used with UpdateSystemFontPayload

src/dispatcher/payloads/UpdateFontSizeDeltaPayload.ts

@@ -17,11 +17,12 @@ limitations under the License.
 import { ActionPayload } from "../payloads";
 import { Action } from "../actions";
 
-export interface UpdateFontSizePayload extends ActionPayload {
+export interface UpdateFontSizeDeltaPayload extends ActionPayload {
-    action: Action.UpdateFontSize;
+    action: Action.UpdateFontSizeDelta;
 
     /**
-     * The font size to set the root to
+     * The delta is added to the current font size.
+     * The delta should be between {@link FontWatcher.MIN_DELTA} and {@link FontWatcher.MAX_DELTA}.
      */
-    size: number;
+    delta: number;
 }

src/i18n/strings/en_EN.json

@@ -2422,9 +2422,7 @@
             "custom_theme_success": "Theme added!",
             "custom_theme_url": "Custom theme URL",
             "font_size": "Font size",
-            "font_size_limit": "Custom font size can only be between %(min)s pt and %(max)s pt",
+            "font_size_default": "%(fontSize)s (default)",
-            "font_size_nan": "Size must be a number",
-            "font_size_valid": "Use between %(min)s pt and %(max)s pt",
             "heading": "Customise your appearance",
             "image_size_default": "Default",
             "image_size_large": "Large",

src/models/Call.ts

@@ -52,11 +52,11 @@ import WidgetStore from "../stores/WidgetStore";
 import { WidgetMessagingStore, WidgetMessagingStoreEvent } from "../stores/widgets/WidgetMessagingStore";
 import ActiveWidgetStore, { ActiveWidgetStoreEvent } from "../stores/ActiveWidgetStore";
 import { getCurrentLanguage } from "../languageHandler";
-import { FontWatcher } from "../settings/watchers/FontWatcher";
 import { PosthogAnalytics } from "../PosthogAnalytics";
 import { UPDATE_EVENT } from "../stores/AsyncStore";
 import { getJoinedNonFunctionalMembers } from "../utils/room/getJoinedNonFunctionalMembers";
 import { isVideoRoom } from "../utils/video-rooms";
+import { FontWatcher } from "../settings/watchers/FontWatcher";
 
 const TIMEOUT_MS = 16000;
 
@@ -687,7 +687,8 @@ export class ElementCall extends Call {
             roomId: roomId,
             baseUrl: client.baseUrl,
             lang: getCurrentLanguage().replace("_", "-"),
-            fontScale: `${(SettingsStore.getValue("baseFontSizeV2") ?? 16) / FontWatcher.DEFAULT_SIZE}`,
+            fontScale: (FontWatcher.getRootFontSize() / FontWatcher.getBrowserDefaultFontSize()).toString(),
+
             analyticsID,
         });
 

src/settings/Settings.tsx

@@ -511,6 +511,9 @@ export const SETTINGS: { [setting: string]: ISetting } = {
         supportedLevels: [SettingLevel.CONFIG],
         default: 0,
     },
+    /**
+     * @deprecated in favor of {@link fontSizeDelta}
+     */
     "baseFontSize": {
         displayName: _td("settings|appearance|font_size"),
         supportedLevels: LEVELS_ACCOUNT_SETTINGS,
@@ -530,12 +533,22 @@ export const SETTINGS: { [setting: string]: ISetting } = {
      * With the transition to Compound we are moving to a base font size
      * of 16px. We're taking the opportunity to move away from the `baseFontSize`
      * setting that had a 5px offset.
-     *
+     * @deprecated in favor {@link fontSizeDelta}
      */
     "baseFontSizeV2": {
         displayName: _td("settings|appearance|font_size"),
         supportedLevels: [SettingLevel.DEVICE],
-        default: FontWatcher.DEFAULT_SIZE,
+        default: "",
+        controller: new FontSizeController(),
+    },
+    /**
+     * This delta is added to the browser default font size
+     * Moving from `baseFontSizeV2` to `fontSizeDelta` to replace the default 16px to --cpd-font-size-root (browser default font size) + fontSizeDelta
+     */
+    "fontSizeDelta": {
+        displayName: _td("settings|appearance|font_size"),
+        supportedLevels: [SettingLevel.DEVICE],
+        default: FontWatcher.DEFAULT_DELTA,
         controller: new FontSizeController(),
     },
     "useCustomFontSize": {

src/settings/controllers/FontSizeController.ts

@@ -16,7 +16,7 @@ limitations under the License.
 
 import SettingController from "./SettingController";
 import dis from "../../dispatcher/dispatcher";
-import { UpdateFontSizePayload } from "../../dispatcher/payloads/UpdateFontSizePayload";
+import { UpdateFontSizeDeltaPayload } from "../../dispatcher/payloads/UpdateFontSizeDeltaPayload";
 import { Action } from "../../dispatcher/actions";
 import { SettingLevel } from "../SettingLevel";
 
@@ -34,9 +34,9 @@ export default class FontSizeController extends SettingController {
             dis.fire(Action.MigrateBaseFontSize);
         } else if (newValue !== "") {
             // Dispatch font size change so that everything open responds to the change.
-            dis.dispatch<UpdateFontSizePayload>({
+            dis.dispatch<UpdateFontSizeDeltaPayload>({
-                action: Action.UpdateFontSize,
+                action: Action.UpdateFontSizeDelta,
-                size: newValue,
+                delta: newValue,
             });
         }
     }

src/settings/watchers/FontWatcher.ts

@@ -22,20 +22,19 @@ import { Action } from "../../dispatcher/actions";
 import { SettingLevel } from "../SettingLevel";
 import { UpdateSystemFontPayload } from "../../dispatcher/payloads/UpdateSystemFontPayload";
 import { ActionPayload } from "../../dispatcher/payloads";
-import { clamp } from "../../utils/numbers";
 
 export class FontWatcher implements IWatcher {
     /**
-     * Value indirectly defined by Compound.
+     * This Compound value is using `100%` of the default browser font size.
-     * All `rem` calculations are made from a `16px` values in the
+     * It allows EW to use the browser's default font size instead of a fixed value.
-     * @vector-im/compound-design-tokens package
+     * All the Compound font size are using `rem`, they are relative to the root font size
-     *
+     * and therefore of the browser font size.
-     * We might want to move to using `100%` instead so we can inherit the user
-     * preference set in the browser regarding font sizes.
      */
-    public static readonly DEFAULT_SIZE = 16;
+    private static readonly DEFAULT_SIZE = "var(--cpd-font-size-root)";
-    public static readonly MIN_SIZE = FontWatcher.DEFAULT_SIZE - 5;
+    /**
-    public static readonly MAX_SIZE = FontWatcher.DEFAULT_SIZE + 5;
+     * Default delta added to the ${@link DEFAULT_SIZE}
+     */
+    public static readonly DEFAULT_DELTA = 0;
 
     private dispatcherRef: string | null;
 
@@ -54,28 +53,106 @@ export class FontWatcher implements IWatcher {
     }
 
     /**
-     * Migrating the old `baseFontSize` for Compound.
+     * Migrate the base font size from the V1 and V2 version to the V3 version
-     * Everything will becomes slightly larger, and getting rid of the `SIZE_DIFF`
+     * @private
-     * weirdness for locally persisted values
      */
     private async migrateBaseFontSize(): Promise<void> {
-        const legacyBaseFontSize = SettingsStore.getValue("baseFontSize");
+        await this.migrateBaseFontV1toFontSizeDelta();
-        if (legacyBaseFontSize) {
+        await this.migrateBaseFontV2toFontSizeDelta();
-            console.log("Migrating base font size for Compound, current value", legacyBaseFontSize);
+    }
 
+    /**
+     * Migrating from the V1 version of the base font size to the new delta system.
+     * The delta system is using the default browser font size as a base
+     * Everything will become slightly larger, and getting rid of the `SIZE_DIFF`
+     * weirdness for locally persisted values
+     * @private
+     */
+    private async migrateBaseFontV1toFontSizeDelta(): Promise<void> {
+        const legacyBaseFontSize = SettingsStore.getValue<number>("baseFontSize");
+        // No baseFontV1 found, nothing to migrate
+        if (!legacyBaseFontSize) return;
+
+        console.log(
+            "Migrating base font size -> base font size V2 -> font size delta for Compound, current value",
+            legacyBaseFontSize,
+        );
+
+        // Compute the V1 to V2 version before migrating to fontSizeDelta
+        const baseFontSizeV2 = this.computeBaseFontSizeV1toV2(legacyBaseFontSize);
+
+        // Compute the difference between the V2 and the fontSizeDelta
+        const delta = this.computeFontSizeDeltaFromV2BaseFontSize(baseFontSizeV2);
+
+        await SettingsStore.setValue("fontSizeDelta", null, SettingLevel.DEVICE, delta);
+        await SettingsStore.setValue("baseFontSize", null, SettingLevel.DEVICE, 0);
+        console.log("Migration complete, deleting legacy `baseFontSize`");
+    }
+
+    /**
+     * Migrating from the V2 version of the base font size to the new delta system
+     * @private
+     */
+    private async migrateBaseFontV2toFontSizeDelta(): Promise<void> {
+        const legacyBaseFontV2Size = SettingsStore.getValue<number>("baseFontSizeV2");
+        // No baseFontV2 found, nothing to migrate
+        if (!legacyBaseFontV2Size) return;
+
+        console.log("Migrating base font size V2 for Compound, current value", legacyBaseFontV2Size);
+
+        // Compute the difference between the V2 and the fontSizeDelta
+        const delta = this.computeFontSizeDeltaFromV2BaseFontSize(legacyBaseFontV2Size);
+
+        await SettingsStore.setValue("fontSizeDelta", null, SettingLevel.DEVICE, delta);
+        await SettingsStore.setValue("baseFontSizeV2", null, SettingLevel.DEVICE, 0);
+        console.log("Migration complete, deleting legacy `baseFontSizeV2`");
+    }
+
+    /**
+     * Compute the V2 font size from the V1 font size
+     * @param legacyBaseFontSize
+     * @private
+     */
+    private computeBaseFontSizeV1toV2(legacyBaseFontSize: number): number {
         // For some odd reason, the persisted value in user storage has an offset
         // of 5 pixels for all values stored under `baseFontSize`
         const LEGACY_SIZE_DIFF = 5;
+
         // Compound uses a base font size of `16px`, whereas the old Element
         // styles based their calculations off a `15px` root font size.
         const ROOT_FONT_SIZE_INCREASE = 1;
 
-            const baseFontSize = legacyBaseFontSize + ROOT_FONT_SIZE_INCREASE + LEGACY_SIZE_DIFF;
+        // Compute the font size of the V2 version before migrating to V3
-
+        return legacyBaseFontSize + ROOT_FONT_SIZE_INCREASE + LEGACY_SIZE_DIFF;
-            await SettingsStore.setValue("baseFontSizeV2", null, SettingLevel.DEVICE, baseFontSize);
-            await SettingsStore.setValue("baseFontSize", null, SettingLevel.DEVICE, "");
-            console.log("Migration complete, deleting legacy `baseFontSize`");
     }
+
+    /**
+     * Compute the difference between the V2 font size and the default browser font size
+     * @param legacyBaseFontV2Size
+     * @private
+     */
+    private computeFontSizeDeltaFromV2BaseFontSize(legacyBaseFontV2Size: number): number {
+        const browserDefaultFontSize = FontWatcher.getRootFontSize();
+
+        // Compute the difference between the V2 font size and the default browser font size
+        return legacyBaseFontV2Size - browserDefaultFontSize;
+    }
+
+    /**
+     * Get the root font size of the document
+     * Fallback to 16px if the value is not found
+     * @returns {number}
+     */
+    public static getRootFontSize(): number {
+        return parseInt(window.getComputedStyle(document.documentElement).getPropertyValue("font-size"), 10) || 16;
+    }
+
+    /**
+     * Get the browser default font size
+     * @returns {number} the default font size of the browser
+     */
+    public static getBrowserDefaultFontSize(): number {
+        return this.getRootFontSize() - SettingsStore.getValue<number>("fontSizeDelta");
     }
 
     public stop(): void {
@@ -84,7 +161,7 @@ export class FontWatcher implements IWatcher {
     }
 
     private updateFont(): void {
-        this.setRootFontSize(SettingsStore.getValue("baseFontSizeV2"));
+        this.setRootFontSize(SettingsStore.getValue<number>("fontSizeDelta"));
         this.setSystemFont({
             useBundledEmojiFont: SettingsStore.getValue("useBundledEmojiFont"),
             useSystemFont: SettingsStore.getValue("useSystemFont"),
@@ -95,13 +172,13 @@ export class FontWatcher implements IWatcher {
     private onAction = (payload: ActionPayload): void => {
         if (payload.action === Action.MigrateBaseFontSize) {
             this.migrateBaseFontSize();
-        } else if (payload.action === Action.UpdateFontSize) {
+        } else if (payload.action === Action.UpdateFontSizeDelta) {
-            this.setRootFontSize(payload.size);
+            this.setRootFontSize(payload.delta);
         } else if (payload.action === Action.UpdateSystemFont) {
             this.setSystemFont(payload as UpdateSystemFontPayload);
         } else if (payload.action === Action.OnLoggedOut) {
             // Clear font overrides when logging out
-            this.setRootFontSize(FontWatcher.DEFAULT_SIZE);
+            this.setRootFontSize(FontWatcher.DEFAULT_DELTA);
             this.setSystemFont({
                 useBundledEmojiFont: false,
                 useSystemFont: false,
@@ -113,13 +190,14 @@ export class FontWatcher implements IWatcher {
         }
     };
 
-    private setRootFontSize = async (size: number): Promise<void> => {
+    /**
-        const fontSize = clamp(size, FontWatcher.MIN_SIZE, FontWatcher.MAX_SIZE);
+     * Set the root font size of the document
-
+     * @param delta {number} the delta to add to the default font size
-        if (fontSize !== size) {
+     */
-            await SettingsStore.setValue("baseFontSizeV2", null, SettingLevel.DEVICE, fontSize);
+    private setRootFontSize = async (delta: number): Promise<void> => {
-        }
+        // Add the delta to the browser default font size
-        document.querySelector<HTMLElement>(":root")!.style.fontSize = toPx(fontSize);
+        document.querySelector<HTMLElement>(":root")!.style.fontSize =
+            `calc(${FontWatcher.DEFAULT_SIZE} + ${toPx(delta)})`;
     };
 
     public static readonly FONT_FAMILY_CUSTOM_PROPERTY = "--cpd-font-family-sans";

test/components/views/settings/FontScalingPanel-test.tsx

@@ -15,11 +15,10 @@ limitations under the License.
 */
 
 import React from "react";
-import { fireEvent, render, waitFor } from "@testing-library/react";
+import { render } from "@testing-library/react";
 
 import * as TestUtils from "../../../test-utils";
 import FontScalingPanel from "../../../../src/components/views/settings/FontScalingPanel";
-import SettingsStore from "../../../../src/settings/SettingsStore";
 
 describe("FontScalingPanel", () => {
     it("renders the font scaling UI", () => {
@@ -27,19 +26,4 @@ describe("FontScalingPanel", () => {
         const { asFragment } = render(<FontScalingPanel />);
         expect(asFragment()).toMatchSnapshot();
     });
-
-    it("should clamp custom font size when disabling it", async () => {
-        jest.spyOn(SettingsStore, "setValue").mockResolvedValue(undefined);
-        TestUtils.stubClient();
-        const { container, getByText } = render(<FontScalingPanel />);
-        fireEvent.click(getByText("Use custom size"));
-        await waitFor(() => {
-            expect(container.querySelector("input[checked]")).toBeDefined();
-        });
-        fireEvent.change(container.querySelector("#font_size_field")!, { target: { value: "25" } });
-        fireEvent.click(getByText("Use custom size"));
-        await waitFor(() => {
-            expect(container.querySelector("#font_size_field")).toHaveValue(21);
-        });
-    });
 });

test/components/views/settings/__snapshots__/FontScalingPanel-test.tsx.snap

@@ -18,6 +18,117 @@ exports[`FontScalingPanel renders the font scaling UI 1`] = `
     <div
       class="mx_SettingsSubsection_content mx_SettingsSubsection_contentStretch"
     >
+      <div
+        class="mx_Field mx_Field_select mx_FontScalingPanel_Dropdown"
+      >
+        <select
+          id="mx_Field_1"
+          label="Font size"
+          placeholder="Font size"
+          type="text"
+        >
+          <option
+            value="-7"
+          >
+            9
+          </option>
+          <option
+            value="-6"
+          >
+            10
+          </option>
+          <option
+            value="-5"
+          >
+            11
+          </option>
+          <option
+            value="-4"
+          >
+            12
+          </option>
+          <option
+            value="-3"
+          >
+            13
+          </option>
+          <option
+            value="-2"
+          >
+            14
+          </option>
+          <option
+            value="-1"
+          >
+            15
+          </option>
+          <option
+            value="0"
+          >
+            16 (default)
+          </option>
+          <option
+            value="1"
+          >
+            17
+          </option>
+          <option
+            value="2"
+          >
+            18
+          </option>
+          <option
+            value="4"
+          >
+            20
+          </option>
+          <option
+            value="6"
+          >
+            22
+          </option>
+          <option
+            value="8"
+          >
+            24
+          </option>
+          <option
+            value="10"
+          >
+            26
+          </option>
+          <option
+            value="12"
+          >
+            28
+          </option>
+          <option
+            value="14"
+          >
+            30
+          </option>
+          <option
+            value="16"
+          >
+            32
+          </option>
+          <option
+            value="18"
+          >
+            34
+          </option>
+          <option
+            value="20"
+          >
+            36
+          </option>
+        </select>
+        <label
+          for="mx_Field_1"
+        >
+          Font size
+        </label>
+      </div>
       <div
         class="mx_FontScalingPanel_preview mx_EventTilePreview_loader"
       >
@@ -33,83 +144,6 @@ exports[`FontScalingPanel renders the font scaling UI 1`] = `
           />
         </div>
       </div>
-      <div
-        class="mx_FontScalingPanel_fontSlider"
-      >
-        <div
-          class="mx_FontScalingPanel_fontSlider_smallText"
-        >
-          Aa
-        </div>
-        <div
-          class="mx_Slider"
-        >
-          <input
-            aria-label="Font size"
-            autocomplete="off"
-            max="21"
-            min="11"
-            step="1"
-            type="range"
-            value="16"
-          />
-          <output
-            class="mx_Slider_selection"
-            style="left: calc(2px + 50% + 1.2em - 1.2em);"
-          >
-            <span
-              class="mx_Slider_selection_label"
-            >
-              16
-            </span>
-          </output>
-        </div>
-        <div
-          class="mx_FontScalingPanel_fontSlider_largeText"
-        >
-          Aa
-        </div>
-      </div>
-      <span
-        class="mx_Checkbox mx_Checkbox_hasKind mx_Checkbox_kind_solid"
-      >
-        <input
-          id="checkbox_QgU2PomxwK"
-          type="checkbox"
-        />
-        <label
-          for="checkbox_QgU2PomxwK"
-        >
-          <div
-            class="mx_Checkbox_background"
-          >
-            <div
-              class="mx_Checkbox_checkmark"
-            />
-          </div>
-          <div>
-            Use custom size
-          </div>
-        </label>
-      </span>
-      <div
-        class="mx_Field mx_Field_input mx_AppearanceUserSettingsTab_checkboxControlledField"
-      >
-        <input
-          autocomplete="off"
-          disabled=""
-          id="font_size_field"
-          label="Font size"
-          placeholder="16"
-          type="number"
-          value="16"
-        />
-        <label
-          for="font_size_field"
-        >
-          Font size
-        </label>
-      </div>
     </div>
   </div>
 </DocumentFragment>

test/components/views/settings/tabs/user/__snapshots__/AppearanceUserSettingsTab-test.tsx.snap

@@ -247,6 +247,117 @@ exports[`AppearanceUserSettingsTab should render 1`] = `
             <div
               class="mx_SettingsSubsection_content mx_SettingsSubsection_contentStretch"
             >
+              <div
+                class="mx_Field mx_Field_select mx_FontScalingPanel_Dropdown"
+              >
+                <select
+                  id="mx_Field_1"
+                  label="Font size"
+                  placeholder="Font size"
+                  type="text"
+                >
+                  <option
+                    value="-7"
+                  >
+                    9
+                  </option>
+                  <option
+                    value="-6"
+                  >
+                    10
+                  </option>
+                  <option
+                    value="-5"
+                  >
+                    11
+                  </option>
+                  <option
+                    value="-4"
+                  >
+                    12
+                  </option>
+                  <option
+                    value="-3"
+                  >
+                    13
+                  </option>
+                  <option
+                    value="-2"
+                  >
+                    14
+                  </option>
+                  <option
+                    value="-1"
+                  >
+                    15
+                  </option>
+                  <option
+                    value="0"
+                  >
+                    16 (default)
+                  </option>
+                  <option
+                    value="1"
+                  >
+                    17
+                  </option>
+                  <option
+                    value="2"
+                  >
+                    18
+                  </option>
+                  <option
+                    value="4"
+                  >
+                    20
+                  </option>
+                  <option
+                    value="6"
+                  >
+                    22
+                  </option>
+                  <option
+                    value="8"
+                  >
+                    24
+                  </option>
+                  <option
+                    value="10"
+                  >
+                    26
+                  </option>
+                  <option
+                    value="12"
+                  >
+                    28
+                  </option>
+                  <option
+                    value="14"
+                  >
+                    30
+                  </option>
+                  <option
+                    value="16"
+                  >
+                    32
+                  </option>
+                  <option
+                    value="18"
+                  >
+                    34
+                  </option>
+                  <option
+                    value="20"
+                  >
+                    36
+                  </option>
+                </select>
+                <label
+                  for="mx_Field_1"
+                >
+                  Font size
+                </label>
+              </div>
               <div
                 class="mx_FontScalingPanel_preview mx_EventTilePreview_loader"
               >
@@ -262,83 +373,6 @@ exports[`AppearanceUserSettingsTab should render 1`] = `
                   />
                 </div>
               </div>
-              <div
-                class="mx_FontScalingPanel_fontSlider"
-              >
-                <div
-                  class="mx_FontScalingPanel_fontSlider_smallText"
-                >
-                  Aa
-                </div>
-                <div
-                  class="mx_Slider"
-                >
-                  <input
-                    aria-label="Font size"
-                    autocomplete="off"
-                    max="21"
-                    min="11"
-                    step="1"
-                    type="range"
-                    value="16"
-                  />
-                  <output
-                    class="mx_Slider_selection"
-                    style="left: calc(2px + 50% + 1.2em - 1.2em);"
-                  >
-                    <span
-                      class="mx_Slider_selection_label"
-                    >
-                      16
-                    </span>
-                  </output>
-                </div>
-                <div
-                  class="mx_FontScalingPanel_fontSlider_largeText"
-                >
-                  Aa
-                </div>
-              </div>
-              <span
-                class="mx_Checkbox mx_Checkbox_hasKind mx_Checkbox_kind_solid"
-              >
-                <input
-                  id="checkbox_QgU2PomxwK"
-                  type="checkbox"
-                />
-                <label
-                  for="checkbox_QgU2PomxwK"
-                >
-                  <div
-                    class="mx_Checkbox_background"
-                  >
-                    <div
-                      class="mx_Checkbox_checkmark"
-                    />
-                  </div>
-                  <div>
-                    Use custom size
-                  </div>
-                </label>
-              </span>
-              <div
-                class="mx_Field mx_Field_input mx_AppearanceUserSettingsTab_checkboxControlledField"
-              >
-                <input
-                  autocomplete="off"
-                  disabled=""
-                  id="font_size_field"
-                  label="Font size"
-                  placeholder="16"
-                  type="number"
-                  value="16"
-                />
-                <label
-                  for="font_size_field"
-                >
-                  Font size
-                </label>
-              </div>
             </div>
           </div>
           <div

test/models/Call-test.ts

@@ -710,8 +710,8 @@ describe("ElementCall", () => {
             const originalGetValue = SettingsStore.getValue;
             SettingsStore.getValue = <T>(name: string, roomId?: string, excludeDefault?: boolean) => {
                 switch (name) {
-                    case "baseFontSizeV2":
+                    case "fontSizeDelta":
-                        return 12 as T;
+                        return 4 as T;
                     case "useSystemFont":
                         return true as T;
                     case "systemFont":
@@ -720,13 +720,14 @@ describe("ElementCall", () => {
                         return originalGetValue<T>(name, roomId, excludeDefault);
                 }
             };
+            document.documentElement.style.fontSize = "12px";
 
             await ElementCall.create(room);
             const call = Call.get(room);
             if (!(call instanceof ElementCall)) throw new Error("Failed to create call");
 
             const urlParams = new URLSearchParams(new URL(call.widget.url).hash.slice(1));
-            expect(urlParams.get("fontScale")).toBe("0.75");
+            expect(urlParams.get("fontScale")).toBe("1.5");
             expect(urlParams.getAll("font")).toEqual(["OpenDyslexic", "DejaVu Sans"]);
 
             SettingsStore.getValue = originalGetValue;

test/settings/watchers/FontWatcher-test.tsx

@@ -123,6 +123,7 @@ describe("FontWatcher", function () {
         let watcher: FontWatcher | undefined;
 
         beforeEach(() => {
+            document.documentElement.style.fontSize = "14px";
             watcher = new FontWatcher();
         });
 
@@ -132,13 +133,35 @@ describe("FontWatcher", function () {
 
         it("should not run the migration", async () => {
             await watcher!.start();
-            expect(SettingsStore.getValue("baseFontSizeV2")).toBe(16);
+            expect(SettingsStore.getValue("fontSizeDelta")).toBe(0);
         });
 
-        it("should migrate to default font size", async () => {
+        it("should migrate from V1 font size to V3", async () => {
             await SettingsStore.setValue("baseFontSize", null, SettingLevel.DEVICE, 13);
             await watcher!.start();
-            expect(SettingsStore.getValue("baseFontSizeV2")).toBe(19);
+            // 13px (V1 font size) + 5px (V1 offset) + 1px (root font size increase) - 14px (default browser font size) = 5px
+            expect(SettingsStore.getValue("fontSizeDelta")).toBe(5);
+            // baseFontSize should be cleared
+            expect(SettingsStore.getValue("baseFontSize")).toBe(0);
+        });
+
+        it("should migrate from V2 font size to V3 using browser font size", async () => {
+            await SettingsStore.setValue("baseFontSizeV2", null, SettingLevel.DEVICE, 18);
+            await watcher!.start();
+            // 18px - 14px (default browser font size) = 2px
+            expect(SettingsStore.getValue("fontSizeDelta")).toBe(4);
+            // baseFontSize should be cleared
+            expect(SettingsStore.getValue("baseFontSizeV2")).toBe(0);
+        });
+
+        it("should migrate from V2 font size to V3 using fallback font size", async () => {
+            document.documentElement.style.fontSize = "";
+            await SettingsStore.setValue("baseFontSizeV2", null, SettingLevel.DEVICE, 18);
+            await watcher!.start();
+            // 18px - 16px (fallback) = 2px
+            expect(SettingsStore.getValue("fontSizeDelta")).toBe(2);
+            // baseFontSize should be cleared
+            expect(SettingsStore.getValue("baseFontSizeV2")).toBe(0);
         });
     });
 });