90 lines
2.6 KiB
TypeScript
90 lines
2.6 KiB
TypeScript
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/**
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* Utility functions for xterm.js cell dimension access.
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* Centralizes access to xterm's internal renderer API to reduce upgrade risk.
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* Falls back to DOM measurement if the internal API is unavailable.
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*/
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import type { Terminal as XTerm } from "@xterm/xterm";
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export interface CellDimensions {
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width: number;
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height: number;
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}
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// Cache to avoid repeated DOM measurements (invalidated on resize)
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let cachedDims: CellDimensions | null = null;
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let cachedTermId: number = 0;
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let termIdCounter = 0;
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const termIdMap = new WeakMap<XTerm, number>();
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function getTermId(term: XTerm): number {
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let id = termIdMap.get(term);
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if (id === undefined) {
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id = ++termIdCounter;
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termIdMap.set(term, id);
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}
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return id;
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}
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/**
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* Get cell dimensions (width/height in CSS pixels) from an xterm instance.
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* Tries the internal renderer API first (fast path), falls back to DOM measurement.
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*/
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export function getXTermCellDimensions(term: XTerm): CellDimensions {
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// Try xterm core renderer API (fast path)
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const coreAccess = term as XTerm & {
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_core?: { _renderService?: { dimensions?: { css?: { cell?: CellDimensions } } } };
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};
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const coreDims = coreAccess._core?._renderService?.dimensions?.css?.cell;
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if (coreDims && coreDims.width > 0 && coreDims.height > 0) {
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// Update cache while we have a good value
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const id = getTermId(term);
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cachedDims = { width: coreDims.width, height: coreDims.height };
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cachedTermId = id;
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return cachedDims;
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}
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// Check cache (same terminal instance)
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const id = getTermId(term);
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if (cachedDims && cachedTermId === id) {
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return cachedDims;
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}
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// Fallback: measure from DOM (triggers single reflow)
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const dims = measureCellFromDOM(term);
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cachedDims = dims;
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cachedTermId = id;
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return dims;
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}
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/**
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* Measure cell dimensions by inserting a temporary span into the terminal element.
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* Triggers a single reflow (reading offsetWidth + offsetHeight).
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*/
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function measureCellFromDOM(term: XTerm): CellDimensions {
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const element = term.element;
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if (!element) return { width: 8, height: 16 };
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const span = document.createElement("span");
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span.textContent = "W";
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Object.assign(span.style, {
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position: "absolute",
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visibility: "hidden",
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fontFamily: term.options.fontFamily || "monospace",
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fontSize: `${term.options.fontSize}px`,
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lineHeight: "normal",
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});
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element.appendChild(span);
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const width = span.offsetWidth || 8;
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const height = span.offsetHeight || 16;
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span.remove();
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return { width, height };
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}
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/**
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* Invalidate the cached cell dimensions (call on terminal resize).
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*/
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export function invalidateCellDimensionCache(): void {
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cachedDims = null;
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}
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