feat: support 'px' format in lineHeight option

Allow lineHeight to accept a string with 'px' suffix (e.g. '23px') in
addition to the existing numeric multiplier. This enables setting an
absolute pixel line height, which is useful when precise control over
row spacing is needed regardless of font size.

- Update type definitions to accept `number | string`
- Add validation for px string format in OptionsService
- Handle px values in DomRenderer and WebglRenderer dimension calculations
- Update WebGL char atlas config type

Fixes #2612

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

Author: evandroreichert

addons/addon-webgl/src/Types.ts

@@ -40,7 +40,7 @@ export interface ICharAtlasConfig {
   devicePixelRatio: number;
   deviceMaxTextureSize: number;
   letterSpacing: number;
-  lineHeight: number;
+  lineHeight: number | string;
   fontSize: number;
   fontFamily: string;
   fontWeight: FontWeight;

addons/addon-webgl/src/WebglRenderer.ts

@@ -623,14 +623,17 @@ export class WebglRenderer extends Disposable implements IRenderer {
     // cell.
     this.dimensions.device.char.height = Math.ceil(this._charSizeService.height * this._devicePixelRatio);
 
-    // Calculate the device cell height, if lineHeight is _not_ 1, the resulting value will be
-    // floored since lineHeight can never be lower then 1, this guarentees the device cell height
-    // will always be larger than device char height.
-    this.dimensions.device.cell.height = Math.floor(this.dimensions.device.char.height * this._optionsService.rawOptions.lineHeight);
+    // Calculate the device cell height, if lineHeight is _not_ 1 (or is a px string), the
+    // resulting value will be floored since lineHeight can never be lower than 1, this guarantees
+    // the device cell height will always be larger than device char height.
+    const lineHeight = this._optionsService.rawOptions.lineHeight;
+    this.dimensions.device.cell.height = typeof lineHeight === 'string'
+      ? Math.max(Math.floor(parseFloat(lineHeight) * this._devicePixelRatio), this.dimensions.device.char.height)
+      : Math.floor(this.dimensions.device.char.height * lineHeight);
 
     // Calculate the y offset within a cell that glyph should draw at in order for it to be centered
     // correctly within the cell.
-    this.dimensions.device.char.top = this._optionsService.rawOptions.lineHeight === 1 ? 0 : Math.round((this.dimensions.device.cell.height - this.dimensions.device.char.height) / 2);
+    this.dimensions.device.char.top = this.dimensions.device.cell.height === this.dimensions.device.char.height ? 0 : Math.round((this.dimensions.device.cell.height - this.dimensions.device.char.height) / 2);
 
     // Calculate the device cell width, taking the letterSpacing into account.
     this.dimensions.device.cell.width = this.dimensions.device.char.width + Math.round(this._optionsService.rawOptions.letterSpacing);

src/browser/renderer/dom/DomRenderer.ts

@@ -133,7 +133,10 @@ export class DomRenderer extends Disposable implements IRenderer {
     this.dimensions.device.char.width = this._charSizeService.width * dpr;
     this.dimensions.device.char.height = Math.ceil(this._charSizeService.height * dpr);
     this.dimensions.device.cell.width = this.dimensions.device.char.width + Math.round(this._optionsService.rawOptions.letterSpacing);
-    this.dimensions.device.cell.height = Math.floor(this.dimensions.device.char.height * this._optionsService.rawOptions.lineHeight);
+    const lineHeight = this._optionsService.rawOptions.lineHeight;
+    this.dimensions.device.cell.height = typeof lineHeight === 'string'
+      ? Math.max(Math.floor(parseFloat(lineHeight) * dpr), this.dimensions.device.char.height)
+      : Math.floor(this.dimensions.device.char.height * lineHeight);
     this.dimensions.device.char.left = 0;
     this.dimensions.device.char.top = 0;
     this.dimensions.device.canvas.width = this.dimensions.device.cell.width * this._bufferService.cols;

src/common/services/OptionsService.ts

@@ -178,12 +178,26 @@ export class OptionsService extends Disposable implements IOptionsService {
       case 'cursorWidth':
         value = Math.floor(value);
         // Fall through for bounds check
-      case 'lineHeight':
       case 'tabStopWidth':
         if (value < 1) {
           throw new Error(`${key} cannot be less than 1, value: ${value}`);
         }
         break;
+      case 'lineHeight':
+        if (typeof value === 'string') {
+          if (!value.endsWith('px')) {
+            throw new Error(`${key} string value must end with 'px', value: ${value}`);
+          }
+          const parsed = parseFloat(value);
+          if (isNaN(parsed) || parsed < 1) {
+            throw new Error(`${key} must be a number >= 1 when using px format, value: ${value}`);
+          }
+        } else if (typeof value === 'number') {
+          if (value < 1) {
+            throw new Error(`${key} cannot be less than 1, value: ${value}`);
+          }
+        }
+        break;
       case 'minimumContrastRatio':
         value = Math.max(1, Math.min(21, Math.round(value * 10) / 10));
         break;

src/common/services/Services.ts

@@ -243,7 +243,7 @@ export interface ITerminalOptions {
   fontWeightBold?: FontWeight;
   ignoreBracketedPasteMode?: boolean;
   letterSpacing?: number;
-  lineHeight?: number;
+  lineHeight?: number | string;
   linkHandler?: ILinkHandler | null;
   logLevel?: LogLevel;
   logger?: ILogger | null;

typings/xterm.d.ts

@@ -145,9 +145,12 @@ declare module '@xterm/xterm' {
     letterSpacing?: number;
 
     /**
-     * The line height used to render text.
+     * The line height used to render text. When a number is given, it is used
+     * as a multiplier of the character height (must be >= 1). When a string
+     * ending in `'px'` is given (e.g. `'23px'`), it sets an absolute pixel
+     * line height (the parsed value must be >= 1).
      */
-    lineHeight?: number;
+    lineHeight?: number | string;
 
     /**
      * The handler for OSC 8 hyperlinks. Links will use the `confirm` browser