How to Plot a Diagonal Line in C?

[1alph1]

this is quite a simple problem,what i am trying to do is plot a line between any two points on my image, i can plot horizontal lines fine.

below is the part of my code to for the line...

int x1 = 92, y1 = 35, x2 = 150, y2 = 55;

//line between two points

for (x = x1; x <= x2; x++)
{
y = y1;
y2 = y1 + ((y2-y1)/(x2-x1))*(x2-x1);
//line between two points

for (x = x1; x <= x2; x++)
{
y = y1;
y2 = y1 + ((y2-y1)/(x2-x1))*(x2-x1); ?
image[x][y][0] = 255; // red colour component
image[x][y][1] = 255; // green colour compnent
image[x][y][2] = 255; // blue colour compnent
}

}

this plots a straight line from points (x1,y1) to (x2, )
however I am stuck on the y2 value I am not sure on what code to use i know its got somthing to do with the graident?

i also know that...

about a for loop in x running between x1 and x2, and calculating a value of y at each point in x.

Something like

for (x = x1; x <= x2; x++)
{
y = y1 + gradient*(x - x1);
}

Now if the magnitude of the gradient is greater than one you'll need a loop in y calculating x at each point.

And you'll need to check x2 is greater than x1 (and swap them if it's not) or the loop won't work.

any help would be really appericated thanks so much guys!

 

[jtbell]

It sounds like you need the two-point formula for a straight line. See for example this page:

http://www.themathpage.com/alg/slope-of-a-line-2.htm

about halfway down from the top.

 

[1alph1]

ok i see, yes that's a good formula but I am not sure how it would be implemented into the code? i have sex x = x1 this wouldn't work with this formula, i could pre determine the graident from the four points but I am not sure what to do to get y2 to move vertically while y1 remains constant??

 

[mXSCNT]

Sounds like what you need is Bresenham's line algorithm.
http://en.wikipedia.org/wiki/Bresenham's_line_algorithm