如何找到在2点之间移动UIView的剩余距离

Question

SCENARIO

I am working on an application that keeps track of blood glucose levels into a graph. On the graph there are "markings" (ex: -200mg) going in vertical order along the y axis on the right side of the screen and "hours" (ex: -12:00 PM) will be along the x axis on the bottom of the graph. I have to plot out little 'dots' to display what the blood glucose level was throughout the way.

ISSUE

I am trying to calculate how to position the 'dots' in the correct time and mg level and I'm having difficulty calculating the positions. I can access the "markings" and retrieve it's marking.center.x to indicate which 'Time Slot' (x axis) and the marking.center.y to indicate which 'MG Level' the 'dot' needs to go into. Problem is it isn't always exactly 12:00 PM or 200mg where it will need to be placed. In fact that would be very rare.

WHAT I NEED

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Based on the following variables:

dot.mgLevel The dot will already know where it needs to go based on the information retrieved from the medical device. It will know the time and mgLevel to assign itself.

marking.mgLevel The markings will each have evenly distributed values that such as -100mg , -200mg , -300mg ect...

timemarking.timeslot Each time marking on the bottom will each have evenly distributed times allocated every 30 min. Such as -12:00PM , -12:30PM , -1:00PM ect...

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If the dot has a mg Level of 330mg and the closest marking on the mg Level is 300mg, then I need to be able to calculate how much further up the dot needs to move from 300 going towards the 400mg marker.

SO...

If the distance between the markings are 100pt and the dot's mgLevel is 330mg, then I know that I need to move the dot from the 300mg marking toward the 400mg marking by exactly 30pt. That's because it's simple math because the distance between the markings is 100. But in real life it isn't 100, so I need to be able to calculate this.

MY ULTIMATE QUESTION

Say distance between markings is 241 and each marking represents multiples of a hundred. Say my dot has a mgLevel of 412. How do I calculate how far I need to move the dot so that it will be in the correct place?

I THINK?

I think I need to make 241 equal 100%. But I need help.

Answer 1

Distance between markings is 241pt Markings are multiples of 100mg 1mg will occupy 2.41pt. So 412mg will occupy (2.41 * 412) pt. To know how much to move for the next dot, take the difference in mg and multiply by 2.41. In general, if distance between 2 markings in points is d , markings are multiples of m , and desired accuracy is k decimal places, 1mg will occupy g : let divisor = pow(10.0, Double(k)) let g = round((d/m)*divisor) / divisor