Implement GL support for buffer textures

Implement GL support for buffer textures

Adds a new sampler type for buffer textures and implements GL support
for it. The addition of buffer textures unfortunately complicates
textures now because GrTextureParams is not always applicable anymore
and textures can be 1-dimensional.

BUG=skia:
GOLD_TRYBOT_URL= https://gold.skia.org/search2?unt=true&query=source_type%3Dgm&master=false&issue=1785873003

[Chris Dalton, 2016-03-11 08:50:40]

Description was changed from

==========
Implement GL support for buffer textures

Adds a new sampler type for buffer textures and implements GL support
for it. The addition of buffer textures unfortunately complicates
textures now because GrTextureParams is not always applicable anymore
and textures can be 1-dimensional.

BUG=skia:
==========

to

==========
Implement GL support for buffer textures

Adds a new sampler type for buffer textures and implements GL support
for it. The addition of buffer textures unfortunately complicates
textures now because GrTextureParams is not always applicable anymore
and textures can be 1-dimensional.

BUG=skia:
GOLD_TRYBOT_URL=
https://gold.skia.org/search2?unt=true&query=source_type%3Dgm&master=false&is...
==========

[Chris Dalton, 2016-03-11 08:54:46]

cdalton@nvidia.com changed reviewers:
+ bsalomon@google.com, joshualitt@google.com

[Chris Dalton, 2016-03-11 08:54:46]

It's unfortunate that buffer textures add so much complexity. Textures used to
be pretty well defined -- 2 dimensional images with wrap/filter/mipmap
properties. With the addition of buffer texture those properties don't always
apply anymore.

Let me know what you think. This patch may just be what initiates discussions on
how to deal with buffer textures, and that's ok.

[bsalomon, 2016-03-16 15:18:34]

What do you think about creating a new class for buffer textures? Under the hood
they use some of the same GL method (glGenTextures) but they feel fundamentally
different than what a GrTexture is.

[Chris Dalton, 2016-03-16 15:25:21]

On 2016/03/16 15:18:34, bsalomon wrote:
> What do you think about creating a new class for buffer textures? Under the
hood
> they use some of the same GL method (glGenTextures) but they feel
fundamentally
> different than what a GrTexture is.

I think that would make more sense (probably something that needs a discussion
bigger than can be had on the code review site). One gotcha is that
GrTextureAccess would need to be able to reference a regular texture or a buffer
texture, and sometimes it would have GrTextureParams and other times not.

[Chris Dalton, 2016-03-16 15:25:22]

On 2016/03/16 15:18:34, bsalomon wrote:
> What do you think about creating a new class for buffer textures? Under the
hood
> they use some of the same GL method (glGenTextures) but they feel
fundamentally
> different than what a GrTexture is.

I think that would make more sense (probably something that needs a discussion
bigger than can be had on the code review site). One gotcha is that
GrTextureAccess would need to be able to reference a regular texture or a buffer
texture, and sometimes it would have GrTextureParams and other times not.

[bsalomon, 2016-03-16 15:30:57]

On 2016/03/16 15:25:22, Chris Dalton wrote:
> On 2016/03/16 15:18:34, bsalomon wrote:
> > What do you think about creating a new class for buffer textures? Under the
> hood
> > they use some of the same GL method (glGenTextures) but they feel
> fundamentally
> > different than what a GrTexture is.
> 
> I think that would make more sense (probably something that needs a discussion
> bigger than can be had on the code review site). One gotcha is that
> GrTextureAccess would need to be able to reference a regular texture or a
buffer
> texture, and sometimes it would have GrTextureParams and other times not.

Or should we have a base class that generalizes GrTextureAccess? If you want to
setup a VC or what not that works for me. I can pull in others from here.