turn a line into a rectangle

I have a method that draws a line between two points. This works pretty well, but now I want to make this line into a rectangle.

How can I get the points on the left and right side of each of the line points to make it into a rectangle that I can draw?

It is al开发者_如何学Gomost as though I need to somehow figure out how to get perpendicular lines programatically....

I'm guessing you basically want fat lines? Lets assume the line is specified by two points (x0, y0) and (x1, y1) we then have:

float dx = x1 - x0; //delta x
float dy = y1 - y0; //delta y
float linelength = sqrtf(dx * dx + dy * dy);
dx /= linelength;
dy /= linelength;
//Ok, (dx, dy) is now a unit vector pointing in the direction of the line
//A perpendicular vector is given by (-dy, dx)
const float thickness = 5.0f; //Some number
const float px = 0.5f * thickness * (-dy); //perpendicular vector with lenght thickness * 0.5
const float py = 0.5f * thickness * dx;
glBegin(GL_QUADS);
glVertex2f(x0 + px, y0 + py);
glVertex2f(x1 + px, y1 + py);
glVertex2f(x1 - px, y1 - py);
glVertex2f(x0 - px, y0 - py);
glEnd();

Since you're using OpenGL ES I guess you'll have to convert the immediate mode rendering (glBegin, glEnd, etc) to glDrawElements. You'll also have to convert the quad into two triangles.

One final thing, I'm a little tired and uncertain if the resulting quad is counterclockwise or clockwise so turn of backface culling when you try this out (glDisable(GL_CULL)).

Since you've asked this question with OpenGL taged I'll assume that you wish for a solution that is close to OpenGL.

As you know you have two points that make up a line. Lets call them x1,y1 and x2, y2

Lets also assume that x1, y1 is the top left point and x2, y2 is the bottom right.

Your 4 points to plot will be [you need to perserve order to make a rectangle with GL_LINES)

Height:y1-y1   
Width: x2-x1 

(x1, y1)
(x1+width, y1)
(x2, y2)
(x2-width, y2)

drawRect(x,y,w,h)

tl = (x,y) tr = (x+w, y) br = (x+w, y+h) bl = (x, y+h)