Added support for optimised reference image PNGs #80
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@reidmain is anyone still maintaining this project / any chance to get this merged please? |
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@reidmain Any chance for this to being merged? Is the project still being maintained please? PRs seems to be abandoned (this one is opened 10 months with no response) |
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How does this compare to #140? |
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Thanks @alanzeino for having a look. I believe both this and #140 have the same goal and almost identical implementation. This was just waiting and ready here 1.5y before #140 😀 Looking at the code the solution is almost the same as well. |
| // Find image which requires more bytes in memory. We have to normalise both images to context requiring "bigger" memory representation. | ||
| // This allows comparing 2 visually identic images even if their bit representation in file can be different | ||
| // (for example reference images optimised using ImageOptim app). | ||
| // Because both images have the same pixel size, image with more bytes per row is the image dictating the context confix for comparison. |
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nit: config
| // Because both images have the same pixel size, image with more bytes per row is the image dictating the context confix for comparison. | |
| // Because both images have the same pixel size, image with more bytes per row is the image dictating the context config for comparison. |
| size_t minBytesPerRow = MIN(CGImageGetBytesPerRow(self.CGImage), CGImageGetBytesPerRow(image.CGImage)); | ||
| size_t referenceImageSizeBytes = referenceImageSize.height * minBytesPerRow; | ||
| // Find image which requires more bytes in memory. We have to normalise both images to context requiring "bigger" memory representation. | ||
| // This allows comparing 2 visually identic images even if their bit representation in file can be different |
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nit: identical
| // This allows comparing 2 visually identic images even if their bit representation in file can be different | |
| // This allows comparing 2 visually identical images even if their bit representation in file can be different |
This allows to use apps like ImageOptim.app to optimise recorded reference images. Optimising reference image can heavily reduce its size, meaning we need to store less binary data in repo.
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Hey. I faced the same problem as the author and ended up with the same fix. The only concern is that it may fail when one image has more bits per component while the other has more bits per pixel and bytes per row. But this is probably very rare. |
TL;DR: Don't fail test / comparison if recorded saved reference image PNG is optimized using tools like ImageOptim.
Overview
This allows to use apps like ImageOptim.app to optimise recorded reference images. Optimising reference image can heavily reduce its size, meaning we need to store less binary data in repo.
Technical details
The core of this change is the way how
CGContextRefare initialized.Before (original code)
Each context was using
minBytesPerRowto calculate buffer size. However, this was reason of the failure in case of optimized images. ImageOptim will for example reduce color space of the PNG from 32bit to 8bit (monochromatic) where possible. This results inminBytesPerRowbeing wrong value (not big enough to fit runtime rendered snapshot).After (this change)
Contexts are always built based on "bigger" (the one needing more memory) context of the two images (saved reference vs rendered). This means context will always be built based on runtime rendered image. When rendering
CGContextDrawImageto context, both runtime snapshot and loaded optimized reference images are "normalized" to the same context (colorspace etc.).Backwards compatibility
✅ 100% backwards compatible
Optimizing reference images is opt-in, optional and fully backwards compatible. This PR will not impact existing projects which don't use optimized reference images.
Performance impact
✅ None (negligible)
memcmpworks the same.minBytesPerRowpadding optimization, which should have almost no impact.