iPad iOS event tracking - angle of refraction compensation... ??

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iPad iOS event tracking - angle of refraction compensation... ??

I have contacted Autodesk to report a problem with the tracking of the lines drawn and the actual center position of a percision stylus like the Adonit JotPro... Basically the lines track off center to the relative "Top" of the page... Wherever you have the "Top" aligned by turning the iPad it will draw lines above the top of the stylus tip center...

See the post here for a better example... The pictures are upside down it is supposed to be at the top...

https://getsatisfaction.com/sketchbook/topics/adonit_jot_precision_stylus_tracks _at_the_top_of_the_stylus_center

Below is the reply i received from Autodesk...

this offset issue is caused by iOS when it compensates for angle of refraction, so the event positions have an offset, bigger the closer you go to the top of the screen.
This becomes evident with pens that have a clear disk.
There is a technical reason why other apps behave correctly and SketchBook doesn't (for now) but I can't discuss the details.

We will look into this but cannot promise when this fix will be released.

What is this exactly... ?? Why is it necessary for the OS to do this and is there any way to disable it with or without jailbreaking the device... ??

I sure would like to be able to draw normally... =]

Posted on Aug 10, 2013 8:49 PM

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Answer 1

Aug 10, 2013 9:49 PM in response to moon47usaco

"There is a technical reason why other apps behave correctly and SketchBook doesn't (for now) but I can't discuss the details."

This appears to be an acknowledgement by Autodesk that their software is responsible for the error, not iOS.

The OS does this to compensate for the estimated change in line of sight between your eyes, over your finger, to the touchscreen, depending on where you are touching the screen.

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Answer 2

moon47usaco Author

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Aug 10, 2013 10:09 PM in response to andrewbuilder

Thanks for exaplining the intent of the compensation a little more clearly...!!

I think it is more an aknoledgement that they are unable overcome the issue rather than the app is the cause...

In Paper, the only app that i have found to draw correctly, the "in app" pen purchase privew screen the offest occours but when you actually purchase the pen id draws correctly without offset...

This shows that it is most likely the default behavior unless rectified by the program... Since Paper and Apple worked so closely from the beginning they may have had an avantage in overcoming the offset that other developers were not afforded...

Either way it still does not answer the question of wether or not the default compensation can be disabled at all for all applications and not just Paper... !!

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Answer 3

Aug 11, 2013 1:47 AM in response to moon47usaco

I cannot agree I am sorry. It is not that the app is the cause, more that their programmers are yet to piece together the appropriate methods in code to make the correct offset work consistently and without error.

Also short answer... No default compensation cannot be disabled.

It doesn't work like that...

When you touch an iPhone or iPad screen your touch evokes a "touch event" within iOS, that is then interpreted in context by the current app. (Part of the UIKit framework in iOS.)

The software programmer for each app is responsible for how his or her app responds to that touch event.

I guess that the response you received from Adobe was a polite "yes we know it's an issue but have not figured out how to overcome it yet".

I am just beginning to learn to use Sketchbook Mobile for iOS. I notice that they include in the latest release a setting titled "Use Offset Painting". Maybe that might help you? I have not researched this however...

Good luck :)

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