[Mesa-dev] [V3 PATCH 2/8] mesa: Change 4 color component ubyte formats

[Marek Olšák]

On Sat, Jan 18, 2014 at 12:45 AM, Mark Mueller <markkmueller at gmail.com> wrote:
>
>
>
> On Fri, Jan 17, 2014 at 1:24 PM, Marek Olšák <maraeo at gmail.com> wrote:
>>
>> Incorrect. You have to manually check if the pack and unpack functions
>> access the components using bitwise operations or arrays.
>>
>> Consider char pix[]. The array formats use arrays for accessing, for
>> example:
>>
>> char *p = &pix[(y*width+x)*4];
>> p[0] = r;
>> p[1] = g;
>> p[2] = b;
>> p[3] = a;
>>
>> Packed formats use bitwise operators for accessing, for example:
>>
>> uint32_t *p = &pix[(y*width+x)*4];
>> *p = r | (g << 8) | (b << 16) | (a << 24);
>
>
> Hang on, that's precisely what I did and when I tallied up the results from

I thought you hadn't. Nevermind then.

> the manual inspection, the rule I provided below fit. For example, in
> format_pack.c, any pack_ubyte function that does not use a PACK_COLOR_ macro
> is either 32 bits per component, or an odd number of components with 8 or 16
> bits: MESA_FORMAT_R_UNORM8, MESA_FORMAT_RGB_UNORM8. I admit that I messed
> one, which is 16 bit floats - those are arrays too.
>
>
>>
>>
>>
>> It's okay to have both RGBA8 array and packed formats. For example,
>> Gallium has these array formats:
>> PIPE_FORMAT_R8G8B8A8_UNORM
>> PIPE_FORMAT_B8G8R8A8_UNORM
>> PIPE_FORMAT_A8R8G8B8_UNORM
>> PIPE_FORMAT_A8B8G8R8_UNORM
>>
>> And it defines these packed formats by using the array formats
>> according to the CPU architecture:
>>
>> #if defined(PIPE_ARCH_LITTLE_ENDIAN)
>> #define PIPE_FORMAT_RGBA8888_UNORM PIPE_FORMAT_R8G8B8A8_UNORM
>> #define PIPE_FORMAT_BGRA8888_UNORM PIPE_FORMAT_B8G8R8A8_UNORM
>> #define PIPE_FORMAT_ARGB8888_UNORM PIPE_FORMAT_A8R8G8B8_UNORM
>> #define PIPE_FORMAT_ABGR8888_UNORM PIPE_FORMAT_A8B8G8R8_UNORM
>> #elif defined(PIPE_ARCH_BIG_ENDIAN)
>> #define PIPE_FORMAT_ABGR8888_UNORM PIPE_FORMAT_R8G8B8A8_UNORM
>> #define PIPE_FORMAT_ARGB8888_UNORM PIPE_FORMAT_B8G8R8A8_UNORM
>> #define PIPE_FORMAT_BGRA8888_UNORM PIPE_FORMAT_A8R8G8B8_UNORM
>> #define PIPE_FORMAT_RGBA8888_UNORM PIPE_FORMAT_A8B8G8R8_UNORM
>> #endif
>>
>> This way, Gallium has all the possible RGBA8 array formats and also
>> the possible RGBA8 packed formats, so we can use whatever we want.
>
>
> The MESA_FORMATs are used to literally tag the application's Internal
> formats such that the driver can better know the application's intention
> (admittedly I'm also looking beyond _mesa_choose_tex_format, but that is for
> another time). The Array Type formats were proposed to indicate that the
> component order is independent of endianess, whereas Packed Type component
> orders _do_ depend on endianess. Acknowledging these Types is an attempt to
> eradicate the confusion. I have no input about mixing types within Gallium,
> but within Mesa my preference is to adhere to that distinction. I find
> Francisco's method to be less confusing then Gallium's (not just because of
> the helpful comment). Here it is with P Type formats:
>
> /*
>  * Define endian-invariant aliases for some mesa formats that are
>  * defined in terms of their channel layout from LSB to MSB in a
>  * 32-bit word.  The actual byte offsets matter here because the user
>  * is allowed to bit-cast one format into another and get predictable
>  * results.
>  */
> #ifdef MESA_BIG_ENDIAN
> # define MESA_FORMAT_RGBA_8 MESA_FORMAT_A8B8G8R8_UNORM
> # define MESA_FORMAT_RG_16 MESA_FORMAT_G16R16_UNORM
> # define MESA_FORMAT_RG_8 MESA_FORMAT_G8R8_UNORM
> # define MESA_FORMAT_SIGNED_RGBA_8 MESA_FORMAT_A8B8G8R8_SNORM
> # define MESA_FORMAT_SIGNED_RG_16 MESA_FORMAT_G16R16_SNORM
> # define MESA_FORMAT_SIGNED_RG_8 MESA_FORMAT_G8R8_SNORM
> #else
> # define MESA_FORMAT_RGBA_8 MESA_FORMAT_R8G8B8A8_UNORM
> # define MESA_FORMAT_RG_16 MESA_FORMAT_R16G16_UNORM
> # define MESA_FORMAT_RG_8 MESA_FORMAT_R8G8_UNORM
> # define MESA_FORMAT_SIGNED_RGBA_8 MESA_FORMAT_R8G8B8A8_SNORM
> # define MESA_FORMAT_SIGNED_RG_16 MESA_FORMAT_R16G16_SNORM
> # define MESA_FORMAT_SIGNED_RG_8 MESA_FORMAT_R8G8_SNORM
> #endif

I'm not sure what you're trying to say here. It looks the same as
gallium, except that it's the other way around (array formats defined
using packed formats).

Marek