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Fix misalignment of Sixel image slices #17724

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merged 2 commits into from
Aug 15, 2024

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j4james
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@j4james j4james commented Aug 15, 2024

Summary of the Pull Request

When we have a series of image slices of differing widths, which also
don't align with the cell boundaries, we can get rounding errors in the
scaling which makes the different slices appear misaligned.

This PR fixes the issue by removing the 4 pixel width alignment that was
enforced in the ImageSlice class, since that's not actually necessary
when the pixels themselves are already 4 bytes in size. And without
that, the widths should be correctly aligned with the cell boundaries.

References and Relevant Issues

The initial Sixel implementation was added in PR #17421.

Validation Steps Performed

I've confirmed that this fixes the rendering glitches reported in
#17711, and all my existing Sixel tests still work as expected.

PR Checklist

@microsoft-github-policy-service microsoft-github-policy-service bot added Issue-Bug It either shouldn't be doing this or needs an investigation. Area-Rendering Text rendering, emoji, complex glyph & font-fallback issues Product-Terminal The new Windows Terminal. labels Aug 15, 2024
Comment on lines 686 to +688
const auto srcHeight = srcCellSize.height;
const auto dstWidth = srcWidth * dstCellSize.width / srcCellSize.width;
const auto dstHeight = srcHeight * dstCellSize.height / srcCellSize.height;
const auto dstHeight = dstCellSize.height;
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This is just a little optimization that I noticed when investigating the rounding problems. The srcHeight is always srcCellSize.height, so the dstHeight should always be dstCellSize.height.

@j4james j4james marked this pull request as ready for review August 15, 2024 16:15
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j4james commented Aug 15, 2024

I'm assuming the audit failure is because the build server has a new version of the compiler.

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Wow, that's subtle. Thanks!

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DHowett commented Aug 15, 2024

Don't worry about audit mode - #17723

@DHowett DHowett merged commit 65219d4 into microsoft:main Aug 15, 2024
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@PhMajerus
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PhMajerus commented Aug 16, 2024

Thanks for this fix!
I can confirm it fixed my test file, as well as my original observation that made me investigate the issue:
image
image

Being able to display icons in the terminal is so nice, so many new possibilities, I have to write a Sixel conversion component.

@j4james j4james deleted the fix-sixel-scaling-glitch branch December 15, 2024 16:14
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Issue with sixel rendering: stretched bands
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