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problem diff between PIC18F and PIC24F

 
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Rocky



Joined: 26 Apr 2009
Posts: 22
Location: USA

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problem diff between PIC18F and PIC24F
PostPosted: Sat Sep 26, 2009 3:42 pm     Reply with quote
I wrote a graphic application that run perfectly on the PIC24 using
primitive routine like the one below which is driving a line.

On the PIC18F I replaced the 'int' with 'int16'.
All my functions are working fine on the pic24 but don't on the PIC18.
A vertical or horizontal line on the PIC18 draws as a 45 degree line.
I tried simpler algorithms but they all show problems.
Code:

// Note: taken verbatim from Professor McMillan's presentation:
// http://www.cs.unc.edu/~mcmillan/comp136/Lecture6/Lines.html
//
// ************************************************************
void LCDSetLine(int x1, int y1, int x2, int y2, int color)
{
int dy, dx, stepx, stepy, fraction;
dy = y2 - y1;
dx = x2 - x1;

             if (dy < 0)
                {
                   dy = - dy;
                   stepy = - 1;
                }

                else
                {
                   stepy = 1;
                }

                if (dx < 0)
                {
                   dx = - dx;
                   stepx = - 1;
                }

                else
                {
                   stepx = 1;
                }

                dy <<= 1; // dy is now 2 * dy
                dx <<= 1; // dx is now 2 * dx
                LCDSetPixel (x1, y1, color);

                if (dx > dy)
                {
                   fraction = dy - (dx >> 1); // same as 2 * dy - dx
                   while (x1 != x2)
                   {
                      if (fraction >= 0)
                      {
                         y1 += stepy;
                         fraction -= dx; // same as fraction -= 2 * dx
                      }

                      x1 += stepx;
                      fraction += dy; // same as fraction -= 2 * dy
                      LCDSetPixel (x1, y1, color);
                   }
                }

                else
                {
                   fraction = dx - (dy >> 1);

                   while (y1 != y2)
                   {
                      if (fraction >= 0)
                      {
                         x1 += stepx;
                         fraction -= dy;
                      }

                      y1 += stepy;
                      fraction += dx;
                      LCDSetPixel (x1, y1, color);
                   }
                }
             }





with this simpler algorithm the problem appears if y1>y2 or x1>x2.

Code:
void lineSimple(int16 x0, int16 y0, int16 x1, int16 y1, int8 color)
    {
        int16 dx,dy,i;
        float m,b;
        dx = x1 - x0;   //PROBLEM IS IF X0>X1 OR Y0>Y1
        dy = y1 - y0;

        LCDSetPixel(x0, y0,color);
        if (dx > dy) {
            m =  (float)dy / (float) dx;
            b = y0 - m*x0;
            dx = (dx < 0) ? -1 : 1;
            while (x0 != x1) {
                x0 = x0 + dx;
                LCDSetPixel(x0, (int16)(m*x0 + b),color);
            }
        }
        else
            if (dy != 0) {
            m =  (float)dx / (float) dy;
            b = x0 - m*y0;
            dy = (dy < 0) ? -1 : 1;
            while (y0 != y1) {
                y0 = y0 + dy;
                LCDSetPixel( (int16)(m*x0 + b), y0,color);
            }   
        }
    }
Again, everything works fine on the PIC24F.

Thanks for any help.
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PCM programmer



Joined: 06 Sep 2003
Posts: 21708

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PostPosted: Sat Sep 26, 2009 4:05 pm     Reply with quote
Note that in the CCS PCH compiler (and PCB and PCM), integer data types
are 'unsigned' by default. If you want a signed value, you need to
declare it explicitly. Example:
Code:
signed int16 dy;
Rocky



Joined: 26 Apr 2009
Posts: 22
Location: USA

View user's profile Send private message

problem diff between PIC18F and PIC24F
PostPosted: Sun Sep 27, 2009 12:02 am     Reply with quote
Thank you PCM that was the problem.

PCM programmer wrote:
Note that in the CCS PCH compiler (and PCB and PCM), integer data types
are 'unsigned' by default. If you want a signed value, you need to
declare it explicitly. Example:
Code:
signed int16 dy;

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