Merge pull request #857 from wader/webp-lossless

webp: Decode width, height and flags for lossless webp
wader · Jan 20, 2024 · a13808d · a13808d
2 parents 422dd65 + b0421df
commit a13808d
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diff --git a/format/riff/testdata/4x4.lossless.webp b/format/riff/testdata/4x4.lossless.webp
diff --git a/format/riff/testdata/4x4.lossless.webp.fqtest b/format/riff/testdata/4x4.lossless.webp.fqtest
@@ -0,0 +1,18 @@
+# convert -size 4x4 "xc:#000" -define webp:lossless=true 4x4.lossless.webp
+$ fq -d webp dv 4x4.lossless.webp
+    |00 01 02 03 04 05 06 07 08 09 0a 0b 0c 0d 0e 0f|0123456789abcdef|.{}: 4x4.lossless.webp (webp) 0x0-0x22 (34)
+0x00|52 49 46 46                                    |RIFF            |  id: "RIFF" 0x0-0x4 (4)
+0x00|            1a 00 00 00                        |    ....        |  size: 26 0x4-0x8 (4)
+0x00|                        57 45 42 50            |        WEBP    |  format: "WEBP" (valid) 0x8-0xc (4)
+    |                                               |                |  chunks[0:1]: 0xc-0x22 (22)
+    |                                               |                |    [0]{}: chunk 0xc-0x22 (22)
+0x00|                                    56 50 38 4c|            VP8L|      id: "VP8L" 0xc-0x10 (4)
+0x10|0e 00 00 00                                    |....            |      size: 14 0x10-0x14 (4)
+0x10|            2f                                 |    /           |      signature: 0x2f (valid) 0x14-0x15 (1)
+0x10|               03 c0 00 00                     |     ....       |      width_height_flags: 49155 0x15-0x19 (4)
+    |                                               |                |      width: 4
+    |                                               |                |      height: 4
+    |                                               |                |      alpha_is_used: false
+    |                                               |                |      version_number: 0
+0x10|                           07 10 11 fd 0f 44 44|         .....DD|      data: raw bits 0x19-0x22 (9)
+0x20|ff 03|                                         |..|             |
diff --git a/format/riff/testdata/4x4.fqtest → format/riff/testdata/4x4.webp.fqtest b/format/riff/testdata/4x4.fqtest → format/riff/testdata/4x4.webp.fqtest
diff --git a/format/riff/webp.go b/format/riff/webp.go
@@ -52,6 +52,26 @@ func webpDecode(d *decode.D) any {
 			case "VP8":
 				d.Format(&vp8FrameGroup, nil)
 				return false, nil
+			case "VP8L":
+				d.FieldU8("signature", d.UintAssert(0x2f), scalar.UintHex)
+				n := d.FieldU32("width_height_flags")
+				// TODO: replace with "bit endian" decoding
+				b0 := (n >> 24) & 0xff
+				b1 := (n >> 16) & 0xff
+				b2 := (n >> 8) & 0xff
+				b3 := (n >> 0) & 0xf
+				width := b3 | (b2&0b0011_111)<<8
+				width += 1
+				height := (b2&0b1100_0000)>>6 | b1<<8 | (b0&0b0000_1111)<<16
+				height += 1
+				alphaIsUsed := b3&0b0001_0000 != 0
+				versionNumber := (b3 & 0b1110_0000) >> 5
+				d.FieldValueUint("width", width)
+				d.FieldValueUint("height", height)
+				d.FieldValueBool("alpha_is_used", alphaIsUsed)
+				d.FieldValueUint("version_number", versionNumber)
+				d.FieldRawLen("data", d.BitsLeft())
+				return false, nil
 			case "VP8X":
 				d.FieldU2("reserved0")
 				d.FieldBool("icc_profile")