Hi everyone.

I am building a sort of x, y axis cnc machine and I'm having trouble implementing bresenham's algorithm.

More specifically I have a question over the 'steep' variable. The code I'm using is based (heavily) on that found in the LCD library source. All the examples I have found are for drawing pixels, and as I understand it, when a line is 'steep' the code swaps the x and y axis controllers before drawing. However, when using motors, each motor can mechanically only control one axis - you can't swap them. How do I edit my code to reflect this?

My general problem is that I don't fully understand what it's doing so when I look at other examples, like the drawbot, I can't get much use out of them.

I'm using arduino Duemilanove, and the adafruit motor shield with windows 7.

My code is below (it's an early version so please excuse the quality) Any advice is much appreciated.

Thanks.

`void bresLine( int x0, int y0, int x1, int y1) {`

int Dx = x1 - x0;

int Dy = y1 - y0;

int steep = (abs(Dy) >= abs(Dx));

if (steep) {

int a = x0;

int b = y0;

x0=b;

y0=a;

a = x1;

b = y1;

x1=b;

y1=a;

// recompute Dx, Dy after swap

Dx = x1 - x0;

Dy = y1 - y0;

}

int xstep = 1;

if (Dx < 0) {

xstep = -1;

Dx = -Dx;

}

int ystep = 1;

if (Dy < 0) {

ystep = -1;

Dy = -Dy;

}

// not objects - * is pointer to memory store

// location for motor objects defined at top

// 'referencing'

// basically creating a new name for the object that can be played with

AF_Stepper* xMotor = NULL;

AF_Stepper* yMotor = NULL;

int TwoDy = 2*Dy;

int TwoDyTwoDx = TwoDy - 2*Dx; // 2*Dy - 2*Dx

int E = TwoDy - Dx; //2*Dy - Dx

int y = y0;

int xDraw, yDraw;

for (int x = x0; x != x1; x += xstep) {

if (steep) {

yMotor = &motorCO2;

xMotor = &motorTime;

xDraw = y;

yDraw = x;

}

else {

yMotor = &motorTime;

xMotor = &motorCO2; // xmotor can mechanically only control time

xDraw = x;

yDraw = y;

}

(*xMotor).step(1, FORWARD, INTERLEAVE);//ORIGINAL

if (E > 0) {

(*yMotor).step(1, BACKWARD, INTERLEAVE);//ORIGINAL

E += TwoDyTwoDx; //E += 2*Dy - 2*Dx;

y = y + ystep;

}

else {

(*yMotor).step(1, BACKWARD, INTERLEAVE);//ORIGINAL

E += TwoDy; //E += 2*Dy;

}

}

}