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Re: [Public WebGL] Adding internalformat param to all texImage2d variants
On 18 May 2010, at 19:00, Chris Marrin wrote:
> On May 17, 2010, at 5:57 PM, Vladimir Vukicevic wrote:
>> ----- "Kenneth Russell" <email@example.com> wrote:
>> On Fri, May 14, 2010 at 4:06 PM, Chris Marrin <firstname.lastname@example.org> wrote:
>>> I would feel comfortable doing that if the browser implementors agree that this is information we can get from the HTML image element.
>> WebKit would currently always return RGBA as the internal format, or
>> perhaps RGB if we could determine that the original image has no alpha
>> channel. We might be able to improve the precision of this query over
>> time. Does this sound acceptable and/or useful?
>> We would do the same for now. Would be straightforward to improve in the future.
> That doesn't solve the X3DOM problem today. Unless they add an internalformat property to ImageTexture, there would be no way to get a 1 or 2 channel image into the system.
> FWIW, WebKit remembers whether or not an image has an alpha channel as an optimization. I haven't looked at the code, but I suspect it would not be hard to remember if the image has 1 or 2 channels as well. If we were to add getTexLevelParameter() to the spec as Ken suggests, we could return this information.
> Here's how I think it would work. We would add an internalformat param to all texImage2D() forms that don't currently have it. We would also add getTexLevelParameter() and all the enums described here:
> Some of the queried values would return default values, e.g., TEXTURE_DEPTH (always 1), TEXTURE_BORDER (always 0), etc.
> If you pass one of the legal internalformat enums to texImage2D() it will convert the source image into that format. In that case getTexLevelParameter would always return that value for gl.TEXTURE_INTERNAL_FORMAT. You can also pass NONE which would convert the image to the "original" format, according to the table:
> 1 channel: LUMINANCE
> 2 channel: LUMINANCE_ALPHA
> 3 channel: RGB
> 4 channel: RGBA
> Note that there is no way to create an ALPHA texture from a 1 channel image. This is a problem in X3D as well. There is no way I know of to create an ImageTexture that is alpha-only. I don't think this is a problem. You'd just have to know the image you're loading is 1 channel and then set internalformat to ALPHA.
> The form of texImage2D which takes an ArrayBufferView would not all NONE as an internalformat and would generate a GL error.
> How does all that sound?
Sounds perfect! And I still believe this is not only useful for X3DOM. Getting e.g. an alpha-mask as single-channel texture into your system is also useful for other systems.
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Dr. Johannes Behr
Leiter Projektbereich VR
Fraunhofer-Institut für Graphische Datenverarbeitung IGD
Fraunhoferstr. 5 | 64283 Darmstadt | Germany
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