Support for loading/saving 'native' premultiplied WIC content

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Assessment

Difficulty
4/5
Estimated time
3-5 days
Newbie friendliness
30/100
Issue type
Feature
Clarity
Mostly clear
Activity status
Stale
Tech stack
cpp

Research direction

Start by tracing the WIC loader's conversion to straight alpha and the DDS writer's metadata handling. Review the listed TIFF/WIC pixel formats and the direct-load DXGI mappings, then verify that native premultiplied data is preserved on load and the metadata flag is honored on save.

Written by the indexing model from the issue text.

Description

enhancement

As part of the support for premultiplied alpha, the library will load DDS files with 'native' pm alpha data and preserve it with a metadata flag to indicate this, and the DDS writer respects this as well.

The WIC loader will currently always convert to 'straight alpha' before returning the data. The majority of the WIC built-in codecs do not support 'native' pm alpha pixel formats. There are one case that could potentially store 'native' pm alpha data.

TIFF

  • GUID_WICPixelFormat32bppPBGRA
  • GUID_WICPixelFormat64bppPRGBA
  • GUID_WICPixelFormat128bppPRGBAFloat

These are all the WIC native pixel formats for pmalpha, although they are not returned by most of the built-in native codecs. They primarily exist for conversions.

  • GUID_WICPixelFormat32bppPRGBA
  • GUID_WICPixelFormat32bppPBGRA
  • GUID_WICPixelFormat64bppPRGBA
  • GUID_WICPixelFormat64bppPBGRA
  • GUID_WICPixelFormat128bppPRGBAFloat
  • GUID_WICPixelFormat64bppPRGBAHalf (WIC2+)

This work item would be to include these in the 'direct-load' DXGI mappings to avoid any conversion and then setting the metadata flag, and the converse.

Dominant language
C++
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