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Re: [Public WebGL] Move flipY and asPremultipliedAlpha parameters out of DOM helpers

On 2010-05-20 19:00, Gregg Tavares wrote:

On Thu, May 20, 2010 at 9:53 AM, Chris Marrin <cmarrin@apple.com <mailto:cmarrin@apple.com>> wrote:

On May 20, 2010, at 9:23 AM, Gregg Tavares wrote:

    On Thu, May 20, 2010 at 8:53 AM, Chris Marrin <cmarrin@apple.com
    <mailto:cmarrin@apple.com>> wrote:

On May 19, 2010, at 7:40 PM, Gregg Tavares wrote:

        > ...
        > What I don't get is why the need for these conversions? If
        you load a grayscale image as RGB you'll get the same visual
        result as LUMINANCE. So it seems like the valid reason to do
        these conversions is for memory savings since you can always
        create RGB or RGBA textures that will give you the same
        visual result.

        I don't see how loading a grayscale as RGB is the same as
        LUMINANCE. The OpenGL texturing engine deals with LUMINANCE
        textures differently from RGB. The problem the information
        that an original image was one channel is lost in the browser
        implementations. Even if not (if the browsers were forced to
        pass along the original image format information)
        implementations would have to have internal format conversion
        to get the image into the right format. So why not expose
        that to the author?

Can you point out the difference between an RGB image where R == G == B and a LUMINANCE texture? I'm unaware of this difference.

I feel very old. There was a time that LUMINANCE textures behaved differently that RGB in the face of the various texturing modes. Those are all gone in a shader based world. So you're right, there is no difference.

As far as I can tell there is no difference. There's also no difference between an RGBA image were R == G == B and a LUMINANCE_ALPHA texture.

    So arguably, the only point in providing the conversions is
    memory savings. Otherwise there's no functional difference.

Right, but I don't think we can underestimate the significance of that memory savings, especially in embedded devices. It can easily mean the difference between content working and exhausting memory. So I reiterate my opinion that we should add internalformat to texImage2D in the 4 cases that take HTML objects.

And if the reason for doing this is memory savings then we need to add support for 565 5551 and 4444. All of which are supported by OpenGL ES 2.0 (and therefore WebGL)

That means just adding internalFormat to texImage2D is not enough.

Either we are trying to do this for memory savings or we aren't.

Adding only internal format will save memory in some cases and adding support for 16 bit format will save more memory in some cases. I don't really see why it has to be all or nothing, that 16 bit format can save more memory does not change the fact that exposing internal format will save some memory in some cases. If one is easier to add than the other, why not just add the easiest one and save a little bit of memory?

I don't really think it will be easy to add guessing of internal format based on the input image in a reliable way though, so I think we need to be very careful about how we expose the internal format if we do so.


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