How to calculate the Rect of a row of N boxes filling up a length L with S space between them

c, geometry, graphics

Solution

I think that despite your effort, this question is a bit unclear. Here's my attempt, though.

The equation that you describes in the title is:

N*x + (N-1)*S = L

Solving that for x gives us the width necessarry for each box:

x = (L - (N-1)*S) / N

This would result in code similar to something like this:

CGContextRef context = UIGraphicsGetCurrentContext(); 

int barSegments = 8;

CGFloat barStartX = 96;
CGFloat barStartY = 64.0;
CGFloat barTotalWidth = 196.0;

CGFloat barHeight = 64;
CGFloat barGutter = 8;
CGFloat barWidth = (barTotalWidth - (barSegments-1)*barGutter) / barSegments;

for (int segmentNumber = 0; segmentNumber < barSegments; ++segmentNumber) {

        // get the box rect
        CGRect segment = CGRectMake(barStartX + ((barWidth + barGutter) * segmentNumber), barStartY , barWidth, barHeight);

        // plot box
        CGContextFillRect(context, segment);
}

Problem

This problem must have been solved a million times, but Google has not been my friend. I need to programmatically space a set of boxes to fill a certain length and be separated by a certain distance. This is what I want: alt text http://img257.imageshack.us/img257/3362/spacingiwant.png Here is what I'm getting: alt text http://img194.imageshack.us/img194/3506/spacingiget.png Since I'm working in Objective-C using Core Graphics, I need a series of Rects that I can draw or drop an image into. My naive attempt draws a set of boxes with a certain spacing but leaves a space at the end. Here is my code, which is in a drawRect: method ``` CGContextRef context = UIGraphicsGetCurrentContext(); CGFloat barStartX = 96; CGFloat barStartY = 64.0; CGFloat barWidth = 16; CGFloat barHeight = 64; CGFloat barGutter = 8; int barSegments = 8; for (int segmentNumber = 0; segmentNumber <= (barSegments - 1); ++segmentNumber) { // get the box rect CGRect segment = CGRectMake(barStartX + (barWidth * segmentNumber), barStartY , barWidth - barGutter, barHeight); // plot box CGContextFillRect(context, segment); } ``` Before I create an impenetrable monstrosity of one-off code that even I won't understand 6 months from now, I'm wondering if there is a general solution to this spacing problem. The answer doesn't have to be in Objective-C, as long as it's somewhat C-like. Readability has priority over performance considerations.

Original source