Manipulating user input for price calculations

Hi guys,

I have the height/width plugin installed to be able to calculate the price on cm2. This works fine, but the price should be just a little bit different and so I wish to "manipulate" the users input.

I cut signs for on cars/vans and I buy my supplies on a roll that's either 30.5cm wide of 61cm wide.
If someone wants to order a sign that's 100x10cm, I will have to purchase a 30.5cm roll. With my current price per cm2 I will therefor spend more then I will earn and will have to charge the customer atleast 100x15cm. Therefor I need to "recalculate" the height that's been given by the customer with the following:

roundup( height / 15 ) * 15 (with 10cm as height it will return 15, with 16 as height it will return 30 and so on) but only when all items are being put in the cart ofcourse.

and use that to multiply by the width for the total cm2 and multiply that by the price per cm2.

This would mean that the price of one 100x15cm will be the same as three 100x5cm, so finally, I want to add an x amount per quantity ordered.

My cutter won't really mind making one of 100x15cm of three of 100x5cm, but I will have the handling cost for applying the transfer tape.

After all these calculations, I give 15% discount for 5+ and 25% discount for 10+, but I recon I can make a coupon for that to take care of that.

I wonder if this can be done.

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Thanks for your attention times

Thanks Nicolas,

I've now edited the file and changed the two lines to

$quantity = $quantity*$product->length*round(($product->width/15),0)*15;

That works, but will test some more when having multiple items in the cart.

Got it all working now Thanks for the pointer in the right direction.

Would it be wise to completely rename the plugin to have it work with 2 different custom fields to make sure it won't interfere with future calculations?

Thanks Nicolas.
Have a great new year and best wishes for the team for 2021. A year in which I will bother you again