Support JPEG compression #583
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with parameters of generation
thirdparty/stb_image_write.h
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| stbiw__putc(s, param_length >> 8); // no need to mask, length < 65536 | ||
| stbiw__putc(s, param_length & 0xFF); | ||
| s->func(s->context, (void*)"parameters", strlen("parameters") + 1); // std::string is zero-terminated | ||
| s->func(s->context, (void*)parameters, param_length - 2 - strlen("parameters") - 1); |
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Might be missing a zero-termination for parameters with length above 65522 (0xFFFF - strlen("parameters") - 1 - 1)
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@idostyle, thanks for review.
JPEG comment block:
comment_marker { 0xFF, 0xFE /* comment marker */ }
comment_body {
uint16be comment_body.length(),
"comment" /* std::string terminates with 0 for compatibility with C strings */
}
Comment length can be 2..65535 bytes, according to https://www.w3.org/Graphics/JPEG/itu-t81.pdf, "Table B.8 – Comment segment parameter sizes and values".
size_t param_length = std::min(2 + strlen("parameters") + 1 + strlen(parameters) + 1, (size_t) 0xFFFF);
// maker_length + len('parameters') + 0 + params.length() + 0,
// truncated to 65535 bytes, so comment can be 65535 - 2 - 10 - 1 - 1 = 65521 bytes.
s->func(s->context, (void*)parameters, param_length - 2 - strlen("parameters") - 1);
// 65535 - 2 /* marker*/ - 10 - 1 /* 'parameters' + 0 */
Second 0, terminating params, is not substracted, therefore it will be written.
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@idostyle, I finally got it, you're right, despite that length of comment block is limited, it should always be terminated with 0, for safety. Fixed.
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Nice. I'm surprised stb_image doesn't support metadata by default. |
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Thank you for your contribution. |
JPEG quality is simply set to 90, to not complicate command options.
And thanks for the program! 🙂