|
14 | 14 | * limitations under the License. |
15 | 15 | */ |
16 | 16 |
|
| 17 | +import { arrayHasDiff } from "./arrays"; |
| 18 | + |
17 | 19 | export function mayBeAnimated(mimeType: string): boolean { |
18 | | - return ["image/gif", "image/webp"].includes(mimeType); |
| 20 | + return ["image/gif", "image/webp", "image/png", "image/apng"].includes(mimeType); |
19 | 21 | } |
20 | 22 |
|
21 | 23 | function arrayBufferRead(arr: ArrayBuffer, start: number, len: number): Uint8Array { |
22 | 24 | return new Uint8Array(arr.slice(start, start + len)); |
23 | 25 | } |
24 | 26 |
|
| 27 | +function arrayBufferReadInt(arr: ArrayBuffer, start: number): number { |
| 28 | + const dv = new DataView(arr, start, 4); |
| 29 | + return dv.getUint32(0); |
| 30 | +} |
| 31 | + |
25 | 32 | function arrayBufferReadStr(arr: ArrayBuffer, start: number, len: number): string { |
26 | 33 | return String.fromCharCode.apply(null, arrayBufferRead(arr, start, len)); |
27 | 34 | } |
28 | 35 |
|
29 | 36 | export async function blobIsAnimated(mimeType: string, blob: Blob): Promise<boolean> { |
30 | | - if (mimeType === "image/webp") { |
31 | | - // Only extended file format WEBP images support animation, so grab the expected data range and verify header. |
32 | | - // Based on https://developers.google.com/speed/webp/docs/riff_container#extended_file_format |
33 | | - const arr = await blob.slice(0, 17).arrayBuffer(); |
34 | | - if ( |
35 | | - arrayBufferReadStr(arr, 0, 4) === "RIFF" && |
36 | | - arrayBufferReadStr(arr, 8, 4) === "WEBP" && |
37 | | - arrayBufferReadStr(arr, 12, 4) === "VP8X" |
38 | | - ) { |
39 | | - const [flags] = arrayBufferRead(arr, 16, 1); |
40 | | - // Flags: R R I L E X _A_ R (reversed) |
41 | | - const animationFlagMask = 1 << 1; |
42 | | - return (flags & animationFlagMask) != 0; |
43 | | - } |
44 | | - } else if (mimeType === "image/gif") { |
45 | | - // Based on https://gist.github.com/zakirt/faa4a58cec5a7505b10e3686a226f285 |
46 | | - // More info at http://www.matthewflickinger.com/lab/whatsinagif/bits_and_bytes.asp |
47 | | - const dv = new DataView(await blob.arrayBuffer(), 10); |
48 | | - |
49 | | - const globalColorTable = dv.getUint8(0); |
50 | | - let globalColorTableSize = 0; |
51 | | - // check first bit, if 0, then we don't have a Global Color Table |
52 | | - if (globalColorTable & 0x80) { |
53 | | - // grab the last 3 bits, to calculate the global color table size -> RGB * 2^(N+1) |
54 | | - // N is the value in the last 3 bits. |
55 | | - globalColorTableSize = 3 * Math.pow(2, (globalColorTable & 0x7) + 1); |
| 37 | + switch (mimeType) { |
| 38 | + case "image/webp": { |
| 39 | + // Only extended file format WEBP images support animation, so grab the expected data range and verify header. |
| 40 | + // Based on https://developers.google.com/speed/webp/docs/riff_container#extended_file_format |
| 41 | + const arr = await blob.slice(0, 17).arrayBuffer(); |
| 42 | + if ( |
| 43 | + arrayBufferReadStr(arr, 0, 4) === "RIFF" && |
| 44 | + arrayBufferReadStr(arr, 8, 4) === "WEBP" && |
| 45 | + arrayBufferReadStr(arr, 12, 4) === "VP8X" |
| 46 | + ) { |
| 47 | + const [flags] = arrayBufferRead(arr, 16, 1); |
| 48 | + // Flags: R R I L E X _A_ R (reversed) |
| 49 | + const animationFlagMask = 1 << 1; |
| 50 | + return (flags & animationFlagMask) != 0; |
| 51 | + } |
| 52 | + break; |
56 | 53 | } |
57 | 54 |
|
58 | | - // move on to the Graphics Control Extension |
59 | | - const offset = 3 + globalColorTableSize; |
| 55 | + case "image/gif": { |
| 56 | + // Based on https://gist.github.com/zakirt/faa4a58cec5a7505b10e3686a226f285 |
| 57 | + // More info at http://www.matthewflickinger.com/lab/whatsinagif/bits_and_bytes.asp |
| 58 | + const dv = new DataView(await blob.arrayBuffer(), 10); |
| 59 | + |
| 60 | + const globalColorTable = dv.getUint8(0); |
| 61 | + let globalColorTableSize = 0; |
| 62 | + // check first bit, if 0, then we don't have a Global Color Table |
| 63 | + if (globalColorTable & 0x80) { |
| 64 | + // grab the last 3 bits, to calculate the global color table size -> RGB * 2^(N+1) |
| 65 | + // N is the value in the last 3 bits. |
| 66 | + globalColorTableSize = 3 * Math.pow(2, (globalColorTable & 0x7) + 1); |
| 67 | + } |
60 | 68 |
|
61 | | - const extensionIntroducer = dv.getUint8(offset); |
62 | | - const graphicsControlLabel = dv.getUint8(offset + 1); |
63 | | - let delayTime = 0; |
| 69 | + // move on to the Graphics Control Extension |
| 70 | + const offset = 3 + globalColorTableSize; |
64 | 71 |
|
65 | | - // Graphics Control Extension section is where GIF animation data is stored |
66 | | - // First 2 bytes must be 0x21 and 0xF9 |
67 | | - if ((extensionIntroducer & 0x21) && (graphicsControlLabel & 0xF9)) { |
68 | | - // skip to the 2 bytes with the delay time |
69 | | - delayTime = dv.getUint16(offset + 4); |
| 72 | + const extensionIntroducer = dv.getUint8(offset); |
| 73 | + const graphicsControlLabel = dv.getUint8(offset + 1); |
| 74 | + let delayTime = 0; |
| 75 | + |
| 76 | + // Graphics Control Extension section is where GIF animation data is stored |
| 77 | + // First 2 bytes must be 0x21 and 0xF9 |
| 78 | + if ((extensionIntroducer & 0x21) && (graphicsControlLabel & 0xF9)) { |
| 79 | + // skip to the 2 bytes with the delay time |
| 80 | + delayTime = dv.getUint16(offset + 4); |
| 81 | + } |
| 82 | + |
| 83 | + return !!delayTime; |
70 | 84 | } |
71 | 85 |
|
72 | | - return !!delayTime; |
| 86 | + case "image/png": |
| 87 | + case "image/apng": { |
| 88 | + // Based on https://stackoverflow.com/a/68618296 |
| 89 | + const arr = await blob.arrayBuffer(); |
| 90 | + if (arrayHasDiff([ |
| 91 | + 0x89, |
| 92 | + 0x50, 0x4E, 0x47, |
| 93 | + 0x0D, 0x0A, |
| 94 | + 0x1A, |
| 95 | + 0x0A, |
| 96 | + ], Array.from(arrayBufferRead(arr, 0, 8)))) { |
| 97 | + return false; |
| 98 | + } |
| 99 | + |
| 100 | + for (let i = 8; i < blob.size;) { |
| 101 | + const length = arrayBufferReadInt(arr, i); |
| 102 | + i += 4; |
| 103 | + const type = arrayBufferReadStr(arr, i, 4); |
| 104 | + i += 4; |
| 105 | + |
| 106 | + switch (type) { |
| 107 | + case "acTL": |
| 108 | + return true; |
| 109 | + case "IDAT": |
| 110 | + return false; |
| 111 | + } |
| 112 | + i += length + 4; |
| 113 | + } |
| 114 | + break; |
| 115 | + } |
73 | 116 | } |
74 | 117 |
|
75 | 118 | return false; |
|
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