Question

I have a for loop and inside that integer x will increase from 533 to 813. That means 280 increments. In side the same loop I want to decrease y’s value from 300 to 200 when above happens. Which means when x is 533 y must be 300 and when x is 813 y must be 200. I know this can do by decrease y’s value by 100/280 in each iteration. But both are integers.

Here are some code sample i used but it is not working.:

for(int i = 0; i < b.getSize(); i++) {
            x = b.getCar(i).getPosX();
            b.getCar(i).setPosX(++x);
            if(x >= ((getWidth() / 2) - 140) && x < ((getWidth() / 2) + 140)){
                y = b.getCar(i).getPosY();
                y = (double)(y - (10.0f / 28.0f));
                b.getCar(i).setPosY((int)y);                    
            }
        }

How can I possibly do this. Thanks!

Answer 1

There are two solutions, a simple and a complex one. The simple one:

y = yoff + (int)( (double) height * x / width )

where yoff = 300, height = -100, width = 813-533. Basically, you do a floating point operation and then you round the result.

Alternatively, the same can be done using pure integer math using the Bresenham line algorithm but that would take a lot more code.