riot-web/src/ImageUtils.ts

/*
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)
 */
export function thumbHeight(fullWidth: number, fullHeight: number, thumbWidth: number, thumbHeight: number): number;
export function thumbHeight(
    fullWidth: number | undefined,
    fullHeight: number | undefined,
    thumbWidth: number,
    thumbHeight: number,
): null;
export function thumbHeight(
    fullWidth: number | undefined,
    fullHeight: number | undefined,
    thumbWidth: number,
    thumbHeight: number,
): number | null {
    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);
    }
}