How to align rectangles with different width horizontally to center, but keeping the anchor point at the centre of each rectangle?

Question

For example, if I have 2 rectangles, the anchor point is in the centre of the rectangle, one the width is 6 (Red), another is 2 (blue), I want to align them horizontally to the centre like this:

So that the position(also the centre and anchor point) of whole structure is at the origin, the red rectangle should be placed at (-1,0), and the blue rectangle should be placed at (3,0).

This example can be solved by graph and divided into 1 unit segments, but how about if I have arbitrary numbers of rectangles with different width?

How to find the position of each rectangle which the anchor point of each rectangle is at the centre?

Answer 1

Sum the widths of all the rectangles and then divide by 2. This is the distance from the left side of the left-most rectangle to center.

Then for each rectangle, compute the distance from the left side of the left-most rectangle to the rectangle's center point. Subtract this from the first number to find the offset of the rectangle's center point from the center.

Pseudo-code:

Find distance from the left side of the left-most rectangle to center:

int i;
float sum = 0;
for(i = 0; i < rectangle_count; i++)
    sum += rectangles[i].width;
centerpoint = sum / 2.0;

Compute offset of each rectangle from center:

sum = 0.0;
for(i = 0; i < rectangle_count; i++)
{
    // compute offset for this rectangle relative to center:
    rectangles[i].offset = (sum + (rectangles[i].width / 2.0)) - centerpoint;

    sum += rectangles[i].width;
}