86 lines
3.2 KiB
TypeScript
86 lines
3.2 KiB
TypeScript
 
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/**
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* The image the OS shows under the cursor during a drag-out.
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*
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* `startDrag` requires one — the plugin's `image` argument is not optional, and
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* it only accepts a `data:image/png;base64,` URL — so this is drawn rather than
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* shipped as an asset. Drawing it is also what keeps the colours honest: the
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* palette lives in CSS custom properties, and reading them off the document is
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* the only way a raw-pixel preview can still come from the design tokens rather
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* than from hard-coded hexes.
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*/
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/**
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* A 1x1 transparent PNG, used when no 2D canvas is available — jsdom has none,
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* and a webview can refuse a context under memory pressure. `startDrag` needs
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* *an* image, and a drag with an invisible preview is much better than no drag.
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*/
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const TRANSPARENT_PNG =
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"data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAAEAAAABCAYAAAAfFcSJAAAAC0lEQVR4nGNgAAIAAAUAAXpeqz8AAAAASUVORK5CYII=";
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/** Longest filename drawn in full; past this the middle is elided. */
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const MAX_LABEL = 28;
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function cssVar(name: string, fallback: string): string {
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const value = getComputedStyle(document.documentElement).getPropertyValue(name).trim();
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return value || fallback;
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}
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/** Keep both ends of a long name — the extension is the informative half. */
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function elide(label: string): string {
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if (label.length <= MAX_LABEL) return label;
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const head = label.slice(0, MAX_LABEL - 12);
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const tail = label.slice(-9);
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return `${head}…${tail}`;
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}
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export function dragPreviewIcon(label: string): string {
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try {
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const text = elide(label);
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// Cap the scale: the OS draws this at logical size, so a 3x buffer is only
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// bytes over IPC.
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const scale = Math.min(window.devicePixelRatio || 1, 2);
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const height = 24;
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const padding = 8;
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const canvas = document.createElement("canvas");
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// Measuring needs a context, and sizing the canvas resets it — so measure
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// on a throwaway pass, then size, then draw.
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const probe = canvas.getContext("2d");
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if (!probe) return TRANSPARENT_PNG;
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const font = "12px ui-monospace, SFMono-Regular, Menlo, monospace";
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probe.font = font;
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const width = Math.ceil(probe.measureText(text).width) + padding * 2;
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canvas.width = Math.round(width * scale);
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canvas.height = Math.round(height * scale);
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const ctx = canvas.getContext("2d");
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if (!ctx) return TRANSPARENT_PNG;
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ctx.scale(scale, scale);
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ctx.fillStyle = cssVar("--bg-tertiary", "#2a2a2a");
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ctx.strokeStyle = cssVar("--accent", "#6aa8ff");
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ctx.lineWidth = 1;
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if (typeof ctx.roundRect === "function") {
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ctx.beginPath();
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ctx.roundRect(0.5, 0.5, width - 1, height - 1, 4);
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ctx.fill();
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ctx.stroke();
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} else {
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ctx.fillRect(0.5, 0.5, width - 1, height - 1);
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ctx.strokeRect(0.5, 0.5, width - 1, height - 1);
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}
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ctx.font = font;
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ctx.fillStyle = cssVar("--text-primary", "#e6e6e6");
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ctx.textBaseline = "middle";
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ctx.fillText(text, padding, height / 2);
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const url = canvas.toDataURL("image/png");
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// jsdom (and a canvas that failed to encode) answers `data:,` — which the
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// Rust side rejects outright, taking the whole drag with it.
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return url.startsWith("data:image/png;base64,") ? url : TRANSPARENT_PNG;
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} catch {
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return TRANSPARENT_PNG;
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}
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}
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