[Mesa-dev] gallium scaled types

[Marek Olšák]

On Mon, Sep 12, 2011 at 5:48 PM, Roland Scheidegger <sroland at vmware.com> wrote:
> Am 11.09.2011 19:17, schrieb Dave Airlie:
>> On Sun, Sep 11, 2011 at 10:11 AM, Dave Airlie <airlied at gmail.com> wrote:
>>> Hi guys,
>>>
>>> not really finding a great explaination in my 2 minute search, of what
>>> the USCALED and SSCALED types are representative of
>>>
>>> On r600 hw at least we have a SCALED type, which seems to be an
>>> integer in float point format, as well as an INT type which is natural
>>> integers.
>>
>> Talked on irc with calim and mareko, makes sense now, need to add
>> UINT/SINT types
>> will document things maybe a bit more on my way past.
>>
>> will also rename the stencil types.
>
>
> Hmm what's wrong with them?
> USCALED is a unsigned int type which in contrast to UNORM isn't
> normalized but "scaled" to the actual value (so same as UINT really).
> Same for SSCALED which is just signed instead of unsigned.
> And the stencil types seem to fit already.

No, they are not.

SCALED is an int that is automatically converted to float when fetched
by a shader.

The SCALED types are OpenGL's non-normalized *float* vertex formats
that are stored in memory as ints, e.g. glVertexAttribPointer(...
GL_INT ...). There are no SCALED textures or renderbuffers supported
by any hardware or exposed by any API known to me. Radeons seem to be
able to do SCALED types according to the ISA docs, but in practice it
only works with vertex formats and only with SCALED8 and SCALED16
(AFAIK).

Then there should be the standard INT types that are not converted to
float upon shader reads. Those can be specified as vertices by
glVertexAttribIPointer(... GL_INT ...) (note the *I*), or as integer
textures. This is really missing in Gallium.

Marek