LunarG/VulkanTools

screenshot layer format support is unclear, maybe broken

lunarpapillo opened this issue · 0 comments

lunarpapillo commented

This was found during SDK testing at: https://gitlab.khronos.org/vulkan/Vulkan-SDK-Packaging/-/issues/1426

The screenshot layer supports a Format parameter, as per: https://vulkan.lunarg.com/doc/sdk/1.3.275.0/windows/screenshot_layer.html
including:

  • UNORM
  • SNORM
  • USCALED
  • SSCALED
  • UINT
  • SINT
  • SRGB
  • USE_SWAPCHAIN_COLORSPACE

The talbe in the document is useless, repeating Enum Value and Label, having "N/A" as every Description, and claiming that all formats are supported on all platforms.

In reality, attempting to use some of the formats (in particular, UINT and SINT) provokes a cryptic warning message:

screenshot: incompatible output format requested, changing output format to VK_FORMAT_B8G8R8A8_UNORM

which is poor because the listed VK_FORMAT_B8G8R8A8_UNORM is not one of the supported Format values. It seems there's some overloading of the term "format".

Worse, when this substitute format is actually used, the .ppm file is incorrect. PPM requires colors to be specified in RGB order. The BGR order reverses the red and blue channels, changing the apparent colors, so this correct screenshot:

image

ends up being captured as:

image

I expect:

  • the documentation to be useful
  • information on "incompatible" formats is presented
  • the term "format" is used consistently
  • valid .ppm images are always created