sceJpegDecParseHeader and sceJpegDecDecode threw for every down scale
other than 1. SharpProspero's JpegDec.cs documents the factors 1, 2, 4
and 8 and output dimensions that account for the down scale.
Decoder::Jpeg gains DecodeScaled, which decodes through libjpeg-turbo's
scaled inverse DCT, and ScaledDimension, its rounded-up output size.
sceJpegDecParseHeader reports the scaled output size; sceJpegDecDecode
checks the pitch and image buffer against it, writes the scaled image
and packs the output size into its result. A down scale of 1 still
decodes as before. Decode modes other than 0, other down scales and a
down-scaled CMYK or YCCK image still throw.
The JpegDec structures were libScePngDec's under new names. OpenOrbis
jpeg.h and SharpProspero JpegDec.cs agree on a 12-byte create param, a
0x30-byte decode param with a coefficient buffer, decode mode and down
scale, and a 0x24-byte image info that reports the coefficient memory
size, the suitable CSC attribute and the output size.
Accept the CSC attributes 1 and 2 that SharpProspero passes, fill the
output size, component count, coefficient memory size and suitable
attribute, apply the requested alpha, and throw for decode modes other
than 0 and down scales other than 1.
Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com>
boykopovar