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Re: [Public WebGL] Adding internalformat param to all texImage2d variants

On Wed, May 19, 2010 at 00:21, Chris Marrin <cmarrin@apple.com> wrote:
> If I have an image that is 2 channels (LA) and my shader expects it to be RGB, I won't get reasonable results, right? If so I don't think having the format automatically set is very useful.

I assume you would get reasonable results. From a shader perspective
everything returned from texture samplers is expanded to RGBA
regardless the format, so for such a scenario the shader expecting RGB
will get the equivalent "luminance color" (L,L,L,1.0) for (R,G,B,A) -
[sections 3.7 and 3.8 of ES 2.0 spec].

Defining conversions other than the direct conversions defined by ES
for sampling/pixel-packing would probably not be that useful and quite
difficult to define for everyone as Gregg pointed out.
As said earlier it only makes sense for a developer to specify desired
internalformat of a DOM element texture in specific (and useful) cases
: if he has full control of the assets and intended usage, e.g for
sure I only need the alpha-channel from that image - or - I need only
RGB from that image - or - I need luminance from that image that is
known to be L or LA ... but *not* RGB or RGBA).
Hence the need for DOM helpers to support and strongly recommend
0/NONE that performs _no conversion_ from the optimal format used by
an implementation for the give image (it gives same results even if an
implementation loads every image in RGBA, if it can load only
necessary channels as in Chris's table it's only more efficient but
results are the strictly the same).

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