matrix-react-sdk/lib/ImageUtils.js

SDK for matrix.org using React

"use strict";

Object.defineProperty(exports, "__esModule", {
  value: true
});
exports.thumbHeight = thumbHeight;
/*
Copyright 2024 New Vector Ltd.
Copyright 2015, 2016 , 2020 Copyright 2020 The Matrix.org Foundation C.I.C.

SPDX-License-Identifier: AGPL-3.0-only OR GPL-3.0-only
Please see LICENSE files in the repository root for full details.
*/

/**
 * Returns the actual height that an image of dimensions (fullWidth, fullHeight)
 * will occupy if resized to fit inside a thumbnail bounding box of size
 * (thumbWidth, thumbHeight).
 *
 * If the aspect ratio of the source image is taller than the aspect ratio of
 * the thumbnail bounding box, then we return the thumbHeight parameter unchanged.
 * Otherwise we return the thumbHeight parameter scaled down appropriately to
 * reflect the actual height the scaled thumbnail occupies.
 *
 * This is very useful for calculating how much height a thumbnail will actually
 * consume in the timeline, when performing scroll offset calculations
 * (e.g. scroll locking)
 */

function thumbHeight(fullWidth, fullHeight, thumbWidth, thumbHeight) {
  if (!fullWidth || !fullHeight) {
    // Cannot calculate thumbnail height for image: missing w/h in metadata. We can't even
    // log this because it's spammy
    return null;
  }
  if (fullWidth < thumbWidth && fullHeight < thumbHeight) {
    // no scaling needs to be applied
    return fullHeight;
  }
  const widthMulti = thumbWidth / fullWidth;
  const heightMulti = thumbHeight / fullHeight;
  if (widthMulti < heightMulti) {
    // width is the dominant dimension so scaling will be fixed on that
    return Math.floor(widthMulti * fullHeight);
  } else {
    // height is the dominant dimension so scaling will be fixed on that
    return Math.floor(heightMulti * fullHeight);
  }
}
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