76 lines
2.6 KiB
Plaintext
76 lines
2.6 KiB
Plaintext
/*
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* Copyright (C) 2024 Huawei Device Co., Ltd.
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* Licensed under the Apache License, Version 2.0 (the 'License');
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* you may not use this file except in compliance with the License.
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* You may obtain a copy of the License at
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*
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* http://www.apache.org/licenses/LICENSE-2.0
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*
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* Unless required by applicable law or agreed to in writing, software
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* distributed under the License is distributed on an 'AS IS' BASIS,
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* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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* See the License for the specific language governing permissions and
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* limitations under the License.
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*/
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import {
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AtMost,
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CenterInside,
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AtLeast,
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DownsampleStrategy,
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FitCenter,
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DefaultDownSampling,
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} from './DownsampleStartegy';
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export class Downsampler {
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calculateScaling(
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typeValue: string,
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sourceWidth: number, //原始宽高
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sourceHeight: number, //原始宽高
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requestWidth: number, //请求宽高
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requestHeight: number, //请求宽高
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downsampType: DownsampleStrategy,
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): Size {
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if (sourceHeight <= 0 || sourceWidth <= 0) {
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throw new Error(`Invalid width and height, sourceHeight:${sourceHeight}+ sourceWidth:${sourceWidth}`)
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}
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let downsampler = this.getDownsampler(downsampType);
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let scaleFactor: number =
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downsampler.getScaleFactor(sourceWidth, sourceHeight, requestWidth, requestHeight, downsampType);//缩放比
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//基于上一步得出的采样大小，根据不同的图片类型，计算采样后的图片尺寸
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if (typeValue === 'png') {
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return {
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width: Math.floor(sourceWidth / scaleFactor),
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height: Math.floor(sourceHeight / scaleFactor)
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}
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} else if (typeValue === 'webp') {
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return {
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width: Math.round(sourceWidth / scaleFactor),
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height: Math.round(sourceHeight / scaleFactor)
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}
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} else {
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return {
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width: sourceWidth / scaleFactor,
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height: sourceHeight / scaleFactor
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}
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}
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}
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getDownsampler(downsampType: DownsampleStrategy) {
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switch (downsampType) {
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case DownsampleStrategy.FIT_CENTER_MEMORY:
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case DownsampleStrategy.FIT_CENTER_QUALITY:
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return new FitCenter();
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case DownsampleStrategy.AT_MOST:
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return new AtMost();
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case DownsampleStrategy.CENTER_INSIDE_MEMORY:
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case DownsampleStrategy.CENTER_INSIDE_QUALITY:
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return new CenterInside();
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case DownsampleStrategy.AT_LEAST:
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return new AtLeast();
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case DownsampleStrategy.DEFAULT:
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return new DefaultDownSampling();
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default:
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throw new Error('Unsupported downsampling strategy');
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}
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}
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} |