[5.4] Ratio validation - allow precision to be based on size of image

[charliekassel]

The precision required to pass ratio validation is quite strict.

Images must have full pixels dimensions when cropping or resizing an image to a specific ratio, decimals must be rounded either up or down to the nearest pixel. This creates an inaccuracy of the required ratio and the inaccuracy is amplified the smaller the image is.

This PR changes the precision required based on the size of the image.

Precision based on max pixel dimension of image

>>> 100/(100*100)
=> 0.01
>>> 1000/(1000*1000)
=> 0.001
>>> 10000/(10000*10000)
=> 0.0001

Example inaccuracy of ratio based on above image sizes

>>> abs(2/3 - 66/100)
=> 0.0066666666666666
>>> abs(2/3 - 666/1000)
=> 0.00066666666666659
>>> abs(2/3 - 6666/10000)
=> 6.6666666666659E-5

So this change allows these proportions to pass the validation, whereas they would all have failed given a 0.000001 precision factor.

[KKSzymanowski]

I don't get this line:

$precision = $maxDimension / $maxDimension ** 2;

Isn't that equivalent to:

$precision = 1 / $maxDimension;

[themsaid]

@charliekassel why don't we just change the 0.000001?

[charliekassel]

@KKSzymanowski - it is indeed sir. Your math is better than mine.
Adjusted in d3b784d

[themsaid]

@charliekassel can you please share a real world example of the problem? What image size and what ration fails?

[charliekassel]

Expanding on the examples above.
If we wanted an 2/3 ratio image 100px wide the closest we can get is 67px rounded up.
Using the calculation in failsRatioCheck that would be:

abs(2/3 - 67/100); // 67px x 100px - 0.0033333333333334 which is greater that 0.000001 so fails.
abs(2/3 - 66/100); // 66px x 100px - 0.0066666666666666 - fails
abs(2/3 - 667/1000); // 667px x 1000px - 0.00033333333333341 - fails
abs(2/3 - 6667/10000); // 6667px x 10000px - 0.00003333333333333 - fails
abs(2/3 - 66667/100000); // 66667px x 100000px - 0.0000033333333333552 - fails
abs(2/3 - 666667/1000000); // 666667px x 1000000px - 0.00000033333333337993 - passes

So you see for a 2/3 ratio image we need go up to 1 million pixels in width in order to pass current precision rules. That's a pretty big image.

Using a precision based on the size of the maximum dimension for above sizes we would get:

0.0033333333333334 > 0.01 === false // 67px x 100px - passes
0.0066666666666666 > 0.01 === false // 66px x 100px - passes
0.00033333333333341 > 0.001 === false // 667px x 1000px - passes
0.00003333333333333 > 0.0001 === false // 6667px x 10000px - passes
0.0000033333333333552 > 0.00001 === false // 66667px x 100000px - passes
0.00000033333333337993 > 0.000001 === false // 666667px x 1000000px - passes

[charliekassel]

I have added a fixture and a test to assert this works.

[themsaid]

@charliekassel I see now, thanks. I think this is ok