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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -0,0 +1,72 @@ | ||
| /** | ||
| * @license | ||
| * Copyright (c) 2022 Daniel Imms <http://www.growingwiththeweb.com> | ||
| * Released under MIT license. See LICENSE in the project root for details. | ||
| */ | ||
|
|
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| import { assertChunkDataLengthGte, assertChunkPrecedes, assertChunkSinglular, createChunkDecodeWarning } from '../assert.js'; | ||
| import { readText } from '../text.js'; | ||
| import { ChunkPartByteLength, IDecodeContext, IPngChunk, IPngHeaderDetails, IPngMetadataPhysicalScaleOfImageSubject, KnownChunkTypes } from '../types.js'; | ||
|
|
||
| /** | ||
| * `sCAL` Physical scale of image subject | ||
| * | ||
| * Spec: https://www.w3.org/TR/PNG/#11sCAL | ||
| */ | ||
| export function parseChunk(ctx: IDecodeContext, header: IPngHeaderDetails, chunk: IPngChunk): IPngMetadataPhysicalScaleOfImageSubject { | ||
| assertChunkSinglular(ctx, chunk); | ||
| assertChunkPrecedes(ctx, chunk, KnownChunkTypes.IDAT); | ||
| assertChunkDataLengthGte(ctx, chunk, 4); | ||
|
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| // Format: | ||
| // Unit specifier: 1 byte | ||
| // Pixel width: 1 or more bytes (ASCII floating-point) | ||
| // Null separator: 1 byte | ||
| // Pixel height: 1 or more bytes (ASCII floating-point) | ||
| const chunkDataOffset = chunk.offset + ChunkPartByteLength.Length + ChunkPartByteLength.Type; | ||
| const maxOffset = chunkDataOffset + chunk.dataLength; // Ensures reading outside this chunk is not allowed | ||
| let offset = chunkDataOffset; | ||
| const textDecoder = new TextDecoder('latin1'); | ||
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| const unitTypeByte = ctx.view.getUint8(offset); | ||
| let unitType: 'meter' | 'radian'; | ||
| switch (unitTypeByte) { | ||
| case 0: unitType = 'meter'; break; | ||
| case 1: unitType = 'radian'; break; | ||
| default: throw createChunkDecodeWarning(chunk, 'Invalid sCAL unit type', offset); | ||
| } | ||
| offset++; | ||
|
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| let readResult: { bytesRead: number, text: string }; | ||
| readResult = readText(ctx, chunk, textDecoder, undefined, offset, maxOffset, true); | ||
| offset += readResult.bytesRead; | ||
| if (!isValidFloatingPoint(readResult.text)) { | ||
| throw createChunkDecodeWarning(chunk, `Invalid character in floating point number ("${readResult.text}")`, offset); | ||
| } | ||
| const x = parseFloat(readResult.text); | ||
|
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| readResult = readText(ctx, chunk, textDecoder, undefined, offset, maxOffset, false); | ||
| offset += readResult.bytesRead; | ||
| if (!isValidFloatingPoint(readResult.text)) { | ||
| throw createChunkDecodeWarning(chunk, `Invalid character in floating point number ("${readResult.text}")`, offset); | ||
| } | ||
| const y = parseFloat(readResult.text); | ||
|
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| if (x < 0 || y < 0) { | ||
| throw createChunkDecodeWarning(chunk, `Values cannot be negative (${x}, ${y})`, offset); | ||
| } | ||
|
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| return { | ||
| type: 'sCAL', | ||
| pixelsPerUnit: { x, y }, | ||
| unitType | ||
| }; | ||
| } | ||
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| function isValidFloatingPoint(text: string) { | ||
| return ( | ||
| text.match(/^[+-]?[0-9]+\.[0-9]+([eE][+-][0-9]+)?$/) || | ||
| text.match(/^[+-]?[0-9]+\.?([eE][+-][0-9]+)?$/) || | ||
| text.match(/^[+-]?\.[0-9]+([eE][+-][0-9]+)?$/) | ||
| ); | ||
| } |
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