Fresnel Lenses - fernel lens

 2024-09-14 10:16:16

On the linked google doc, I didn't see anything more in there, it looked like a copy of the understanding document with no comments/changes, is that correct?

Given that most guidance (including from Google) is for larger target sizes than the minimum required by this SC, what could more research show that would change the SC?

The comment says "allowing", not "encouraging". The current SC's spacing exception allows a 1x1 px button (so long as it is at least 23px away from any other targets, ie, "presented in isolation").

This (User-agent exception) implies that if the browser fails this, then the content authors must fix it. This conflicts with other guidance like "1.4.13 Content on Hover or Focus". Changing it to "…by the user agent and is not modified by the author" would work...

If light strikes an interface so that there is a 90o angle between the reflected and refracted rays, the reflected light will be linearly polarized. The direction of polarization (the way the electric field vectors point)is parallel to the plane of the interface. The special angle of incidence that produces a 90o angle between the reflected and refracted ray is called the Brewster angle, qp. A little geometry shows that tan(qp) = n2/n1. Why is the reflected light polarized? Let's say the incident light is unpolarized. When the incident light crosses the interface the light is absorbed temporarily by atoms in the seond medium. Electrons in these atoms oscillate back and forth in the direction of the electric field vectors in the refracted ray, perpendicular to the direction the refracted light is traveling. The light is re-emitted by the atoms to form both the reflected and refracted rays. The electric field vectors in the light match the direction the electrons were oscillating, and they must be perpendicular to the direction of propagation of the wave. When light comes in at the Brewster angle the reflected wave has no electric field vectors parallel to the refracted ray, because the electrons do not oscillate along that direction. The reflected wave also has no electric field vectors parallel to the reflected ray, because that's the direction of propagation of the wave. The only direction possible is perpendicular to the plane of the picture, so the reflected ray is linearly polarized. The refracted ray is partly polarized because it has more light with electric field vectors in the plane of the picture than perpendicular to it. If the angle of incidence is something other than 0o and the Brewster angle, the reflected ray is also partly polarized.

How was this (spacing) exception (the note) determined? We have some concerns about the accessibility of targets being spaced out 24px with a target size potentially being allowed at 1px. Allowing smaller target sizes that are presented in isolation, alone in a part of a larger UI, may reduce usability rather than improve it. This exception has the benefit of potentially meeting the intent of the SC (i.e., reducing the number of accidental hits of an adjacent target), but may risk reducing usability by negatively impacting the findability of the target in question.

This (user-agent exception) seems like an opportunity to either push the browser to update to a more accessible default, or to recommend more accessible alternatives. Ideally, some course of action that would maintain a11y would be desirable.

Direction of polarization ofelectromagnetic waves

If a target uses the "essential" exception, I don't think it could have an equivalent control elsewhere. By the definition, anything that meets the essential exception "cannot be achieved in another way that would conform".

The refracted ray is partly polarized because it has more light with electric field vectors in the plane of the picture than perpendicular to it. If the angle of incidence is something other than 0o and the Brewster angle, the reflected ray is also partly polarized.

This is more in line with our concerns that the target size is quite small, especially at an AA-level. We are worried about the churn of having to retrofit targets after further research and consensus (hopefully) justifies a larger target size. :-)

+1 to these points and the feedback raised by @dbjorge that (citing) more studies and research from additional populations would be helpful to ensure the decision is as robust as possible.

“Spacing” and “target offset” seem to be used interchangeably for the same concept. One term should be used to reduce confusion.

Polarisation meaning in Physics

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The example (with the media controls) is there to assist people testing the SC. It is not trying to encourage smaller targets, in fact it saying that smaller targets (that pass) will negatively impact the layout.

The exception came from the prioritisation of not making accidental hits, and that allows for more flexibility. Obviously we do not wish to encourage small targets, but that comes from WCAG defining a baseline rather than a goal.

The restrictions on this SC are more about web practicalities than the user-requirements. For example, WCAG doesn't (and cannot) differentiate between web sites that are used on mobile compared to desktop. Therefore everything has to be compatible with both.

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All of WCAG applies to the web content, not browser chrome. If the target is a scroll bar within the content (e.g. scrollable element), then it would apply. That is the same for non-text contrast, keyboard accessibility, pointer gestures etc. That's an example that could be added to the understanding document.

Thank you for verifying if this was expected! I can view 23 comments in there from September 28 (and five on the first page alone). Could you please try loading the doc again?

We kindly request that the group remove this SC until research is completed for all affected input modalities. and: +1 to these points and the feedback raised by @dbjorge that (citing) more studies and research from additional populations would be helpful to ensure the decision is as robust as possible.

The only research referenced in the Understanding Target Size points to one study specific to small touchscreen devices, while the SC applies to all devices and input modalities. If other research backs this guidance up across everything on the web, then linking to that as well in the documentation should cover this concern.

The special angle of incidence that produces a 90o angle between the reflected and refracted ray is called the Brewster angle, qp. A little geometry shows that tan(qp) = n2/n1. Why is the reflected light polarized? Let's say the incident light is unpolarized. When the incident light crosses the interface the light is absorbed temporarily by atoms in the seond medium. Electrons in these atoms oscillate back and forth in the direction of the electric field vectors in the refracted ray, perpendicular to the direction the refracted light is traveling. The light is re-emitted by the atoms to form both the reflected and refracted rays. The electric field vectors in the light match the direction the electrons were oscillating, and they must be perpendicular to the direction of propagation of the wave. When light comes in at the Brewster angle the reflected wave has no electric field vectors parallel to the refracted ray, because the electrons do not oscillate along that direction. The reflected wave also has no electric field vectors parallel to the reflected ray, because that's the direction of propagation of the wave. The only direction possible is perpendicular to the plane of the picture, so the reflected ray is linearly polarized. The refracted ray is partly polarized because it has more light with electric field vectors in the plane of the picture than perpendicular to it. If the angle of incidence is something other than 0o and the Brewster angle, the reflected ray is also partly polarized.

The answer above was approved by the working group. Note that the understanding document is still undergoing review from multiple issues raised so will change further.

This comment seems to be based on a previous version? There is nothing in the current SC that is encouraging smaller targets, it is a minimum, not an ideal size.

Suggest "meets this criterion with no exceptions" (for the equivalent exception). By a strict reading or perhaps just through gaps in testing this standard seems to allow two equally problematic controls. What if the other target has an essential exception for some reason? If another control "meets this criterion", then that makes it so that the original control ALSO meets the criterion, setting up a potentially problematic loop.

A little geometry shows that tan(qp) = n2/n1. Why is the reflected light polarized? Let's say the incident light is unpolarized. When the incident light crosses the interface the light is absorbed temporarily by atoms in the seond medium. Electrons in these atoms oscillate back and forth in the direction of the electric field vectors in the refracted ray, perpendicular to the direction the refracted light is traveling. The light is re-emitted by the atoms to form both the reflected and refracted rays. The electric field vectors in the light match the direction the electrons were oscillating, and they must be perpendicular to the direction of propagation of the wave. When light comes in at the Brewster angle the reflected wave has no electric field vectors parallel to the refracted ray, because the electrons do not oscillate along that direction. The reflected wave also has no electric field vectors parallel to the reflected ray, because that's the direction of propagation of the wave. The only direction possible is perpendicular to the plane of the picture, so the reflected ray is linearly polarized. The refracted ray is partly polarized because it has more light with electric field vectors in the plane of the picture than perpendicular to it. If the angle of incidence is something other than 0o and the Brewster angle, the reflected ray is also partly polarized.

This comment seems to be based on a previous version? There is nothing in the current SC that is encouraging smaller targets, it is a minimum, not an ideal size.

This example seems to duplicate much of the information above and seems to add more word count without necessarily adding more value. Recommendation would be to clarify the core content above in order to trim this content.

That said, I do think the current spacing exception encourages smaller target sizes in some cases. For example, if an author has a goal of making a certain number of buttons fit side by side within a thin container, the current spacing exception makes that easier to achieve with smaller target sizes:

Recommendation: We kindly request that the group remove this SC until research is completed for all affected input and interaction modalities. Allowing smaller target sizes that are presented in isolation, alone in a part of a larger UI, may reduce usability rather than improve it by negatively impacting the findability of the target in question. We’d like to see both the SC and exceptions supported with more data, and the entire SC to be rewritten to clarify a minimum target size and padding, supported by empirical data, rather than a focus on target spacing. Defining a minimum target size is certainly very important. However, setting a too-small target size at an AA-level, and then trying to increase it later may have severe consequences.

This (text about passing with spacing) is again related to the distinction between “target size” and “visible size”. This clarification essentially states that a target doesn’t need to be both 24 CSS pixels tall and wide; it only needs to be one of them - 24 CSS pixels tall or wide - provided that the other dimension doesn’t have adjacent targets.

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The earlier versions of the SC did describe it as minimum size OR size and spacing. However, it was simpler and conveyed the intent to start with a minimum size.

This comment seems to be based on a previous version? There is nothing in the current SC that is encouraging smaller targets, it is a minimum, not an ideal size.

We aimed for that with the WCAG 2.1 SC for target size, but there are just too many interfaces on the web with smaller targets that would require a complete overhaul and negatively impact other audiences. (Including online document editors.) That requirement is at AAA. Effectively we already have done that, but at AA and AAA.

The note is describing what is considered a target. For example, the entire editing area of a document is considered 'a target'. However, it also allows the selection of a location within that target area. It would not be feasible to make every possible cursor position 24px wide. A volume slider with 100 options would have to be 2400px tall (or wide), which is also not feasible.

The light is re-emitted by the atoms to form both the reflected and refracted rays. The electric field vectors in the light match the direction the electrons were oscillating, and they must be perpendicular to the direction of propagation of the wave. When light comes in at the Brewster angle the reflected wave has no electric field vectors parallel to the refracted ray, because the electrons do not oscillate along that direction. The reflected wave also has no electric field vectors parallel to the reflected ray, because that's the direction of propagation of the wave. The only direction possible is perpendicular to the plane of the picture, so the reflected ray is linearly polarized. The refracted ray is partly polarized because it has more light with electric field vectors in the plane of the picture than perpendicular to it. If the angle of incidence is something other than 0o and the Brewster angle, the reflected ray is also partly polarized.

It isn't an exception, just outlining that content layered above a target doesn't impact how you assess that target. I.e. partially obscuring background targets doesn't suddenly make them fail.

Planeof polarization

We are interpreting this new draft that this SC is not about ensuring a minimum target size; it’s about ensuring a minimum distance between adjacent targets, as illustrated by Figure 8 and Figure 9. A description could be something to the effect of: "Accessible targets for any pointer input must allow a X by X CSS pixel square to be overlaid on top of that target along all possible dimensions [include illustration], without overlapping any adjacent target." The description above with Figures 8 and 9 may be a more clear way of describing the standard and its intent than the current version.

There is currently no intent to change the SC later, except perhaps as part of the WCAG 3 process. Could you explain what/why it would have severe consequences?

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We tried several variations of 'put a square over the target', and others, in this (experimentation doc)[https://docs.google.com/document/d/1qhh9VgBC_6HD2emkvql2Hn83iSChwlhGBs5_E9gkdEM/edit]. It is ok for a minimum size, but it leads to odd results for spacing, particularly in rows of targets.

Direction of polarizationin physics

There is currently no intent to change the SC later, except perhaps as part of the WCAG 3 process. Could you explain what/why it would have severe consequences?

If zoom were a way to pass, nothing would fail. There would be no point in creating the SC. Also, having to zoom in to use targets may itself be difficult for people with mobility impairments, e.g. pinch zooming with tremors.

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Most of the examples have come from questions people have had, but we will do a review of the whole before the next stage.

Target offset is the measure to determine if there is sufficient spacing. That section of the (understanding document)[https://w3c.github.io/wcag/understanding/target-size-minimum.html] has been updated.

Targets that allow for values to be selected spatially based on position within the target are considered one target for the purpose of the success criterion. Examples include sliders with granular values, color pickers displaying a gradient of colors, or editable areas where you position the cursor.”

Linearpolarization

An illustration could help clarify what is meant by this exception: "The requirement does not apply to targets while they are obscured by content displayed as a result of a user interaction or scripted behavior of content"

Allowing smaller target sizes that are presented in isolation, alone in a part of a larger UI, may reduce usability rather than improve it by negatively impacting the findability of the target in question.

Circularpolarization

“Success Criterion 2.5.8 Target Size (Minimum) (Level AA): The size of the target for pointer inputs is at least 24 by 24 CSS pixels, except where:

Please consider the impact that smaller icons could have on certain users, such as those using head-mounted pointing devices, or with fine motor control challenges where the user perceives that they must click a very small target (even if the actual clickable area is larger due to invisible clickable padding, etc.)

On the linked google doc, I didn't see anything more in there, it looked like a copy of the understanding document with no comments/changes, is that correct?

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I think this is a misunderstanding, but I'm not sure how to prevent it. There is no mention or differentiation of the visible size of targets. It also doesn't differentiate between height and width. It could be less than 24px on both axis, if there is sufficient spacing on each axis.

Article (exceptions) should clarify if these guidelines apply to custom styles for scrollbar thumbs/handles, and/or if there are any special considerations in that case.

Direction of polarizationformula

As mentioned, bigger is better but the size is based on web-practicalities, not the ideal size. It is intentionally a baseline size that does not harm (for example) people zooming into an interface with a toolbar. That is also true of the exceptions, they are there to account for things authors cannot adequately control, or whether there are other methods of achieving the same function.

I agree that I would like to see the references in the Understanding Target Size document updated to include a broader set of research. In particular, while I agree with @slauriat that there should be citations that cover a broader range of input modalities and form factors, I also note that the single cited study doesn't include any study participants older than 42 - I'd like to see the SC justified by research that includes a broader representation of users.

Direction of polarizationpdf

Unfortunately, because of those practicalities there is no research that would lead to a blanket requirement for a larger size. In a future version (e.g. WCAG 3) there could be a more nuanced SC which has different size requirements for different controls.

While the SC in its current wording indeed allows for targets to be smaller than 24 x 24 pixels, it takes away the main incentive of reducing target size below 24 x 24 px since the way target size including offset is calculated rules out compressing or packing targets in order to cram more targets into the available viewport space. Very small targets, while not ruled out as long as the minimum inter-target spacing is adhered to, would decrease usability for all users, being hard to perceive/read. They are therefore unlikely design choices by authors in a situation where each target needs a total spacing of 24 x 24 px (including offset).

The definition of “spacing”/”target offset” is atypical for web development: “measures the distance between targets, measured from the farthest point of one target to the nearest point of the adjacent target”. In particular, very few web layout considerations are from the “farthest point” to the “nearest point”, potentially making this difficult to both understand and test. Instead, consider using more standard relationships like padding and margin (e.g. “if the distance between each target such as margin or padding, combined with the height of each target, meets or exceeds 24 pixels”).

Why is the reflected light polarized? Let's say the incident light is unpolarized. When the incident light crosses the interface the light is absorbed temporarily by atoms in the seond medium. Electrons in these atoms oscillate back and forth in the direction of the electric field vectors in the refracted ray, perpendicular to the direction the refracted light is traveling. The light is re-emitted by the atoms to form both the reflected and refracted rays. The electric field vectors in the light match the direction the electrons were oscillating, and they must be perpendicular to the direction of propagation of the wave. When light comes in at the Brewster angle the reflected wave has no electric field vectors parallel to the refracted ray, because the electrons do not oscillate along that direction. The reflected wave also has no electric field vectors parallel to the reflected ray, because that's the direction of propagation of the wave. The only direction possible is perpendicular to the plane of the picture, so the reflected ray is linearly polarized. The refracted ray is partly polarized because it has more light with electric field vectors in the plane of the picture than perpendicular to it. If the angle of incidence is something other than 0o and the Brewster angle, the reflected ray is also partly polarized.

We should be able to help with this after obtaining a few approvals. Would it be sufficient to share the study here and also attend an upcoming group meeting, similar to the Shadows and Outlines/Non Text Contrast approach from 2019?

Clarify that “size” is referring to “target size”, not necessarily “visible size”. In particular this is explained in the exception for Spacing, but given that this is such a key part of understanding the SC, we feel it might be clearer if it was a core part of the requirement and not an Exception.

There is ample research into beneficial target sizes, and extant recommendations both in research and by platform providers that warrant defining minimum target size in a new SC 2.5.8. The target size of 24 x 24px was chosen as a workable compromise between extant recommendations of larger sizes (e.g., Apple’s iPhone Human Interface Guidelines recommend a minimum target size of 44 x 44 px) and the needs of interfaces where a lot of icon-based controls need to be simultaneously available (e.g., in toolbars), evidenced in many existing implementations of web-based applications.

Reiterating this comment from #2695 since I think it's probably better-suited here: I think the "Spacing" exception is especially problematic in that I think the only study referenced in the understanding doc actually provides direct evidence that contradicts the underlying assumption behind the exception!

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Ultimately, this seems like an especially important area to have research, a diverse set of use cases, and a specific set of content structures to keep the SC beneficial, appropriately scoped, clearly testable and verifiable, and attainable.

This (note) should probably specify that the spatial selection is a continuum. A block of cards with 1px radio buttons for selection would pass the standards, even if the targets are a tiny portion of the whole display. This could even encourage creators to reformat things in this manner to bypass other requirements. Many sliders also only have discrete, individual targets for their marks, and can only be clicked in certain places. Controls can be formatted in a way that undermines their own function, and we shouldn't have an exception because it looks a certain way.

The main concern in 2.5.8 Target Size is preventing accidental activation to support users with reduced motor skills. It also benefits users in situations where they are exposed to shaking, e.g. on public transport. The gestation process of the SC went through various iterations of trying to define target size, including setting a minimum size independent of spacing. It appeared that this approach had disadvantages as it would not cover the various interactions of targets with adjacent targets in various situations, such as target overlaps or enclosure of targets in other targets.

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We started at 44px at AA, but couldn't work around objections based on legitimate cases where targets needed to be smaller than that (including for people with low vision).

If the angle of incidence is something other than 0o and the Brewster angle, the reflected ray is also partly polarized.

The understanding documents have not been repositories of research, they are intended to be concise how-to guides for understanding and meeting the SC. Perhaps we should link to the Mobile Accessibility Task Force's original searches? https://www.w3.org/WAI/GL/mobile-a11y-tf/wiki/Summary_of_Research_on_Touch/Pointer_Target_Size

The SC starts with "The size of the target", and the target is a link to the definition ("region of the display that will accept a pointer action"), so it is currently part of the core SC requirement.

This example uses a picture of text to illustrate the exception for inline targets. A text example (rather than a picture of text) may be more clear and accessible

I think that adding more of these references that @detlevhfischer linked earlier would be sufficient to justify the 24 CSS pixel size choice, but I don't think any of those references support the Spacing exception, and I think the specific one linked above is evidence against the Spacing exception as-written (regardless of whether the changes in #2798 are accepted).

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We did consider trying to specify a continuum, but it didn't help. E.g. if 1px selection are the smallest possible option, when is it not a continuum? 2px, 3? Not including this clarification appears to do more harm than good (balancing real uses of it verses potential gaming).

The Spacing exception is built on the assumption that if a target is crowded by other targets, then a user would tend to press on a spot on the desired target which is further away from crowding. But figure 5 in section 5.1 of Target size study for one-handed thumb use on small touchscreen devices does not consistently reflect this assumption! In that study, only buttons that were crowded on their left sides reflected the assumption; for buttons that were crowded above and below, users actually tended to press towards the crowded side.