/*# proc: compute_slope - computes the slope of the line between two points.# proc:# proc: compute_y - given the x coordinate, slope, and another point on the# proc:             line, computes the corresponding y coordinate.# proc: compute_x - computes the x coordinate for a specified y coordinate,# proc:             given a non-zero slope and a point on the line.# proc: pt_intersect - computes the point of intersection between two# proc:                specified lines.# proc: intersect_sides - projects a line within a specified rectangle and# proc:                determines the enpoints of where the line intersects the# proc:                sides.*//************************************************************//*         File Name: LINE.C                                *//*         Package:   Fundamental Line Utilities            *//*         Author:    Michael D. Garris                     *//*         Date:      03/05/91                              *//*                                                          *//*         Contents:  compute_slope()                       *//*                    compute_y()                           *//************************************************************/#include <stdio.h>#include <math.h>#include <values.h>#include <defs.h>/************************************************************//*         Routine:   compute_slope()                       *//*                                                          *//* Compute_slope(), given two coordinate points, returns    *//* the slope of a line connecting the two points.           *//* Note: This routine returns the system's MAXFLOAT for     *//* points vertically aligned.                               *//************************************************************//* x1, y1 - first coordinate point.                         *//* x2, y2 - second coordinate point.                        *//************************************************************/float compute_slope(x1, y1, x2, y2)float x1, y1, x2, y2;{   float f_slope, dx, dy;   dx = (x2 - x1);   if(dx == 0.0)      return(MAXFLOAT);   dy = (y2 - y1);   f_slope = dy/dx;   return(f_slope);}/************************************************************/float compute_y(x, m, x1, y1)float x, m, x1, y1;{   float y;   y = (m * x) - (m * x1) + y1;   return(y);}/***************************************************************************//* compute_x - computes the x coordinate for a specified y coordinate,     *//* given a none-zero slope and a point on the line.                        *//***************************************************************************/float compute_x(y, m, x1, y1)float y, m, x1, y1;{   float x;   if(m == 0.0)      fatalerr("compute_x", "slope is 0.0, so x coordinate cannot be computed",               NULL);   x = ((y - y1)/m) + x1;   return(x);}/***************************************************************************//* pt_intersect - given a point and slope of two lines, computes their     *//* point of intersection. If the lines are parallel, then the routine      *//* retruns FALSE.                                                          *//***************************************************************************/pt_intersect(ix, iy, x1, y1, m1, x2, y2, m2)int *ix, *iy;int x1, y1, x2, y2;float m1, m2;{   *ix = NOT_FOUND;   *iy = NOT_FOUND;   if(m1 == m2)      return(FALSE);   *ix = sround((y2-y1+(m1*x1)-(m2*x2))/(m1-m2));   *iy = sround(y1 + (m1 * ((*ix) - x1)));   return(TRUE);}/***************************************************************************//* intersect_sides - given a point and a slope for a line, projects the    *//* line to the edge of a rectangular region and determines endpoints where *//* the line intersects the edge of the rectangle.                          *//***************************************************************************/intersect_sides(x1, y1, x2, y2, x, y, slope, fw, fh)int *x1, *y1, *x2, *y2;int x, y, fw, fh;float slope;{   float compute_y(), compute_x();   int ty, tx, max_x, max_y;   *x1 = NOT_FOUND;   *y1 = NOT_FOUND;   *x2 = NOT_FOUND;   *y2 = NOT_FOUND;   /* special case, if slope is exactly 0.0 */   if(slope == 0.0){      *x1 = 0;      *y1 = y;      *x2 = fw - 1;      *y2 = y;      return;   }   /* compute y coordinate with x at left edge of image */   ty = sround(compute_y(0.0, slope, (float)x, (float)y));   /* if y coordinate is within image dimensions ... */   max_y = fh - 1;   if(is_in_range(ty, 0, max_y)){      /* store as the 1st point */      *x1 = 0;      *y1 = ty;   }   /* compute x coordinate with y at top edge of image */   tx = sround(compute_x(0.0, slope, (float)x, (float)y));   /* if x coordinate is within image dimensions ... */   max_x = fw - 1;   if(is_in_range(tx, 0, max_x)){      /* if 1st point not yet found ... */      if((*x1 == NOT_FOUND) || (*y1 == NOT_FOUND)){         /* store as 1st point */         *x1 = tx;         *y1 = 0;      }      else{         /* otherwise store as 2nd point */         *x2 = tx;         *y2 = 0;      }   }   /* compute x coordinate with y at bottom edge of image */   tx = sround(compute_x((float)max_y, slope, (float)x, (float)y));   /* if x coordinate is within image dimensions ... */   if(is_in_range(tx, 0, max_x)){      /* if 1st point not yet found ... */      if((*x1 == NOT_FOUND) || (*y1 == NOT_FOUND)){         /* store as 1st point */         *x1 = tx;         *y1 = max_y;      }      else{         /* otherwise store as 2nd point */         *x2 = tx;         *y2 = max_y;      }   }   /* compute y coordinate with x at right edge of image */   ty = sround(compute_y((float)max_x, slope, (float)x, (float)y));   /* if y coordinate is within image dimensions ... */   if(is_in_range(ty, 0, max_y)){      /* store as 2nd point */      *x2 = max_x;      *y2 = ty;   }   /* double check to make sure points are filled in */   if((*x1 == NOT_FOUND) || (*y1 == NOT_FOUND))      fatalerr("intersect_sides", "first intersection point not found", NULL);   if((*x2 == NOT_FOUND) || (*y2 == NOT_FOUND))      fatalerr("intersect_sides", "second intersection point not found", NULL);}