Use xterm's to calc terminal char dimensions if available

Fixes #44608

src/typings/vscode-xterm.d.ts

@@ -606,5 +606,6 @@ declare module 'vscode-xterm' {
 
 		webLinksInit(handler?: (event: MouseEvent, uri: string) => void, options?: ILinkMatcherOptions): void;
 		winptyCompatInit(): void;
+		charMeasure?: { height: number, width: number }
 	}
 }
\ No newline at end of file

src/vs/workbench/parts/terminal/electron-browser/terminalConfigHelper.ts

@@ -14,6 +14,7 @@ import { ITerminalConfiguration, ITerminalConfigHelper, ITerminalFont, IShellLau
 import Severity from 'vs/base/common/severity';
 import { isFedora } from 'vs/workbench/parts/terminal/electron-browser/terminal';
 import { IChoiceService } from 'vs/platform/dialogs/common/dialogs';
+import { Terminal as XTermTerminal } from 'vscode-xterm';
 
 const DEFAULT_LINE_HEIGHT = 1.0;
 
@@ -50,20 +51,12 @@ export class TerminalConfigHelper implements ITerminalConfigHelper {
 	}
 
 	private _measureFont(fontFamily: string, fontSize: number, lineHeight: number): ITerminalFont {
-		// Return cached font if no config changed
-		if (this._lastFontMeasurement &&
-			this._lastFontMeasurement.fontFamily === fontFamily &&
-			this._lastFontMeasurement.fontSize === fontSize &&
-			this._lastFontMeasurement.lineHeight === lineHeight) {
-			return this._lastFontMeasurement;
-		}
-
 		// Create charMeasureElement if it hasn't been created or if it was orphaned by its parent
 		if (!this._charMeasureElement || !this._charMeasureElement.parentElement) {
 			this._charMeasureElement = document.createElement('div');
 			this.panelContainer.appendChild(this._charMeasureElement);
 		}
-		// TODO: This should leverage CharMeasure
+
 		const style = this._charMeasureElement.style;
 		style.display = 'block';
 		style.fontFamily = fontFamily;
@@ -92,7 +85,7 @@ export class TerminalConfigHelper implements ITerminalConfigHelper {
 	 * Gets the font information based on the terminal.integrated.fontFamily
 	 * terminal.integrated.fontSize, terminal.integrated.lineHeight configuration properties
 	 */
-	public getFont(excludeDimensions?: boolean): ITerminalFont {
+	public getFont(xterm?: XTermTerminal, excludeDimensions?: boolean): ITerminalFont {
 		const editorConfig = this._configurationService.getValue<IEditorOptions>('editor');
 
 		let fontFamily = this.config.fontFamily || editorConfig.fontFamily;
@@ -115,6 +108,20 @@ export class TerminalConfigHelper implements ITerminalConfigHelper {
 			};
 		}
 
+		// Get the character dimensions from xterm if it's available
+		if (xterm) {
+			if (xterm.charMeasure && xterm.charMeasure.width && xterm.charMeasure.height) {
+				return {
+					fontFamily,
+					fontSize,
+					lineHeight,
+					charHeight: xterm.charMeasure.height,
+					charWidth: xterm.charMeasure.width
+				};
+			}
+		}
+
+		// Fall back to measuring the font ourselves
 		return this._measureFont(fontFamily, fontSize, lineHeight);
 	}
 

src/vs/workbench/parts/terminal/electron-browser/terminalInstance.ts

@@ -223,7 +223,7 @@ export class TerminalInstance implements ITerminalInstance {
 			return null;
 		}
 
-		const font = this._configHelper.getFont();
+		const font = this._configHelper.getFont(this._xterm);
 
 		// Because xterm.js converts from CSS pixels to actual pixels through
 		// the use of canvas, window.devicePixelRatio needs to be used here in
@@ -243,7 +243,7 @@ export class TerminalInstance implements ITerminalInstance {
 
 	private _getDimension(width: number, height: number): Dimension {
 		// The font needs to have been initialized
-		const font = this._configHelper.getFont();
+		const font = this._configHelper.getFont(this._xterm);
 		if (!font || !font.charWidth || !font.charHeight) {
 			return null;
 		}
@@ -285,7 +285,7 @@ export class TerminalInstance implements ITerminalInstance {
 			Terminal.strings.tooMuchOutput = nls.localize('terminal.integrated.a11yTooMuchOutput', 'Too much output to announce, navigate to rows manually to read');
 		}
 		const accessibilitySupport = this._configurationService.getValue<IEditorOptions>('editor').accessibilitySupport;
-		const font = this._configHelper.getFont(true);
+		const font = this._configHelper.getFont(undefined, true);
 		this._xterm = new Terminal({
 			scrollback: this._configHelper.config.scrollback,
 			theme: this._getXtermTheme(),
@@ -1096,7 +1096,7 @@ export class TerminalInstance implements ITerminalInstance {
 		}
 
 		if (this._xterm) {
-			const font = this._configHelper.getFont();
+			const font = this._configHelper.getFont(this._xterm);
 
 			// Only apply these settings when the terminal is visible so that
 			// the characters are measured correctly.