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[csswg-drafts] [css-images-4] Defining coordinate systems for various types of images.

From: Florian Rivoal via GitHub <sysbot+gh@w3.org>
Date: Wed, 26 Oct 2016 16:35:54 +0000
To: public-css-archive@w3.org
Message-ID: <issues.opened-185446459-1477499752-sysbot+gh@w3.org>
frivoal has just created a new issue for 
https://github.com/w3c/csswg-drafts:

== [css-images-4] Defining coordinate systems for various types of 
images. ==
In the [css-ui-3 spec's definition of the cursor 
property](https://drafts.csswg.org/css-ui-3/#cursor), we find this :
> &lt;x>&lt;y>
>
>The x-coordinate and y-coordinate of the position in the cursor’s 
coordinate system (left/top relative) which represents the precise 
position that is being pointed to.
>>Note: This specification does not define how the coordinate systems 
of the various types of <image> are established, and defers these 
definitions to [CSS4-IMAGES].

This is when discussing the x and y values of the property, that 
position the cursor hotspot in the cursor image.

As far as I can tell, css-images (regardless of level), doesn't do 
that. Did I miss it?

That the origin is at the top left is clear. This also probably means 
that:
* that for a bitmap image the unit is in image pixels
* that for an svg image, the unit is the unitless length integer

However, it isn't clear what this means for a gradient or
an image-set, which has images at multiple resolutions.

The full list of possible <image> values is:

`<image> = 
<url> | <image()> | <image-set()> | <element()> | <cross-fade()> | 
<gradient>`

We need to define this (and css-image seems does seem like the right 
place, so that things just work when new `<image>` values are added).

As for the actual definitions, I propose:
bitmaps
 -> the unit is the image pixel for bitmap images

svg
 -> the svg unit

`<image()>`
 -> the coordinate system of the image you end up loading
    ISSUE: what to do if we fallback to a color?

`<image-set()>`
 -> the coordinate system of the first image in the list

`<element()>`
 -> CSS pixels?

`<cross-fade>`
 -> the coordinate system of the `<cf-mixing-image>`

`<gradient>`
 -> each axis goes from 0 to 100

Please view or discuss this issue at 
https://github.com/w3c/csswg-drafts/issues/652 using your GitHub 
account
Received on Wednesday, 26 October 2016 16:36:00 UTC

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