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|
import type { GraphicStrokeAlign } from "./definitions/shared";
type GraphicRenderContext =
| CanvasRenderingContext2D
| OffscreenCanvasRenderingContext2D;
function createTempCanvas({
width,
height,
}: {
width: number;
height: number;
}): OffscreenCanvas | HTMLCanvasElement {
try {
return new OffscreenCanvas(width, height);
} catch {
const canvas = document.createElement("canvas");
canvas.width = width;
canvas.height = height;
return canvas;
}
}
function applyStroke({
ctx,
path,
strokeWidth,
strokeColor,
}: {
ctx: GraphicRenderContext;
path: Path2D;
strokeWidth: number;
strokeColor: string;
}) {
ctx.strokeStyle = strokeColor;
ctx.lineWidth = strokeWidth;
ctx.stroke(path);
}
export function applyAlignedStroke({
ctx,
path,
strokeWidth,
strokeAlign,
strokeColor,
}: {
ctx: GraphicRenderContext;
path: Path2D;
strokeWidth: number;
strokeAlign: GraphicStrokeAlign;
strokeColor: string;
}): void {
if (strokeWidth <= 0) {
return;
}
if (strokeAlign === "inside") {
ctx.save();
ctx.clip(path);
applyStroke({
ctx,
path,
strokeWidth: strokeWidth * 2,
strokeColor,
});
ctx.restore();
return;
}
if (strokeAlign === "outside") {
const strokeCanvas = createTempCanvas({
width: ctx.canvas.width,
height: ctx.canvas.height,
});
const strokeCtx = strokeCanvas.getContext("2d") as GraphicRenderContext | null;
if (!strokeCtx) {
return;
}
applyStroke({
ctx: strokeCtx,
path,
strokeWidth: strokeWidth * 2,
strokeColor,
});
// Keep only the outer half of the doubled stroke so alpha fills do not
// leave a visible inner stroke behind.
strokeCtx.globalCompositeOperation = "destination-out";
strokeCtx.fill(path);
ctx.drawImage(strokeCanvas, 0, 0);
return;
}
applyStroke({
ctx,
path,
strokeWidth,
strokeColor,
});
}
|
