[Mesa3d-dev] RFC: allow resource_copy_region between different (yet compatabile) formats

[José F. <jfo...@vm...>]

I'd like to know if there's any objection to change the
resource_copy_region semantics to allow copies between different yet
compatible formats, where the definition of compatible formats is:

  "formats for which copying the bytes from the source resource
unmodified to the destination resource will achieve the same effect of a
textured quad blitter"

There is an helper function util_is_format_compatible() to help making
this decision, and these are the non-trivial conversions that this
function currently recognizes, (which was produced by
u_format_compatible_test.c):

  b8g8r8a8_unorm -> b8g8r8x8_unorm
  a8r8g8b8_unorm -> x8r8g8b8_unorm
  b5g5r5a1_unorm -> b5g5r5x1_unorm
  b4g4r4a4_unorm -> b4g4r4x4_unorm
  l8_unorm -> r8_unorm
  i8_unorm -> l8_unorm
  i8_unorm -> a8_unorm
  i8_unorm -> r8_unorm
  l16_unorm -> r16_unorm
  z24_unorm_s8_uscaled -> z24x8_unorm
  s8_uscaled_z24_unorm -> x8z24_unorm
  r8g8b8a8_unorm -> r8g8b8x8_unorm
  a8b8g8r8_srgb -> x8b8g8r8_srgb
  b8g8r8a8_srgb -> b8g8r8x8_srgb
  a8r8g8b8_srgb -> x8r8g8b8_srgb
  a8b8g8r8_unorm -> x8b8g8r8_unorm
  r10g10b10a2_uscaled -> r10g10b10x2_uscaled
  r10sg10sb10sa2u_norm -> r10g10b10x2_snorm

Note that format compatibility is not commutative.

For software drivers this means that memcpy/util_copy_rect() will
achieve the correct result.

For hardware drivers this means that a VRAM->VRAM 2D blit engine will
also achieve the correct result.

So I'd expect no implementation change of resource_copy_region() for any
driver AFAICT. But I'd like to be sure.

Jose