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| 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 | 1x 1x 1x 181x 181x 181x 181x 181x 181x 181x 181x 181x 181x 181x 181x 181x 181x 181x 181x 574x 574x 574x 574x 574x 574x 574x 574x 574x 574x 574x 574x 574x | const VIEWPORT_ELEMENT = 'viewport-element';
const CANVAS_CSS_CLASS = 'cornerstone-canvas';
export const EPSILON = 1e-4;
/**
* Create a canvas and append it to the element
*
* @param element - An HTML Element
* @returns canvas - A Canvas DOM element
*/
function createCanvas(element: Element | HTMLDivElement): HTMLCanvasElement {
const canvas = document.createElement('canvas');
canvas.style.position = 'absolute';
canvas.style.width = '100%';
canvas.style.height = '100%';
canvas.style.imageRendering = 'pixelated';
canvas.classList.add(CANVAS_CSS_CLASS);
element.appendChild(canvas);
return canvas;
}
/**
* Creates an internal div that will contain canvas and SVG layer as children
* @param element - An HTML Element
* @returns div Cornerstone internal div that will include the canvas and SVG
* as its children
*/
export function createViewportElement(element: HTMLDivElement): HTMLDivElement {
const div = document.createElement('div');
div.style.position = 'relative';
div.style.width = '100%';
div.style.height = '100%';
// Hide any canvas elements not viewable
div.style.overflow = 'hidden';
div.classList.add(VIEWPORT_ELEMENT);
element.appendChild(div);
return div;
}
/**
* Create a canvas or returns the one that already exists for a given element.
* It first checks if the element has a canvas, if not it creates one and returns it.
* The canvas is updated for:
* 1. width/height in screen pixels to completely cover the div element
* 2. CSS width/height in CSS pixels to be the size of the physical screen pixels
* width and height (from #1)
* This allows drawing to the canvas and having pixel perfect/exact drawing to
* the physical screen pixels.
*
* @param element - An HTML Element
* @returns canvas a Canvas DOM element
*/
export default function getOrCreateCanvas(
element: HTMLDivElement
): HTMLCanvasElement {
const canvasSelector = `canvas.${CANVAS_CSS_CLASS}`;
const viewportElement = `div.${VIEWPORT_ELEMENT}`;
// Internal div with `relative` positioning to enable absolute positioning
// of the canvas and svg layer.
const internalDiv =
element.querySelector(viewportElement) || createViewportElement(element);
const canvas = (internalDiv.querySelector(canvasSelector) ||
createCanvas(internalDiv)) as HTMLCanvasElement;
// Fit the canvas into the div
const rect = internalDiv.getBoundingClientRect();
const devicePixelRatio = window.devicePixelRatio || 1;
// The width/height is the number of physical pixels which will completely
// cover the div so that no pixels, fractional or full are left uncovered.
// Thus, it is the ceiling of the CSS size times the physical pixels.
// In theory, the physical pixels can be offset from CSS pixels, but in practice
// this hasn't been observed.
const width = Math.ceil(rect.width * devicePixelRatio);
const height = Math.ceil(rect.height * devicePixelRatio);
canvas.width = width;
canvas.height = height;
// Reset the size of the canvas to be the number of physical pixels,
// expressed as CSS pixels, with a tiny extra amount to prevent clipping
// to the next lower size in the physical display.
canvas.style.width = (width + EPSILON) / devicePixelRatio + 'px';
canvas.style.height = (height + EPSILON) / devicePixelRatio + 'px';
return canvas;
}
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