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James Gregory 2013-12-31 11:38:48 +11:00
commit f658bfbb40
203 changed files with 26546 additions and 25801 deletions
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41-01.md
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@ -102,45 +102,47 @@ test whether a polygon is appropriately monotone.
**LISTING 41.1 L41-1.C**
/* Returns 1 if polygon described by passed-in vertex list is monotone with
respect to a vertical line, 0 otherwise. Doesn't matter if polygon is simple
(non-self-intersecting) or not. Tested with Borland C++ in small model. */
```c
/* Returns 1 if polygon described by passed-in vertex list is monotone with
respect to a vertical line, 0 otherwise. Doesn't matter if polygon is simple
(non-self-intersecting) or not. Tested with Borland C++ in small model. */
#include "polygon.h"
#include "polygon.h"
#define SIGNUM(a) ((a>0)?1:((a<0)?-1:0))
#define SIGNUM(a) ((a>0)?1:((a<0)?-1:0))
int PolygonIsMonotoneVertical(struct PointListHeader * VertexList)
{
int i, Length, DeltaYSign, PreviousDeltaYSign;
int NumYReversals = 0;
struct Point *VertexPtr = VertexList->PointPtr;
int PolygonIsMonotoneVertical(struct PointListHeader * VertexList)
{
int i, Length, DeltaYSign, PreviousDeltaYSign;
int NumYReversals = 0;
struct Point *VertexPtr = VertexList->PointPtr;
/* Three or fewer points can't make a non-vertical-monotone polygon */
if ((Length=VertexList->Length) < 4) return(1);
/* Three or fewer points can't make a non-vertical-monotone polygon */
if ((Length=VertexList->Length) < 4) return(1);
/* Scan to the first non-horizontal edge */
PreviousDeltaYSign = SIGNUM(VertexPtr[Length-1].Y - VertexPtr[0].Y);
i = 0;
while ((PreviousDeltaYSign == 0) && (i < (Length-1))) {
PreviousDeltaYSign = SIGNUM(VertexPtr[i].Y - VertexPtr[i+1].Y);
i++;
}
/* Scan to the first non-horizontal edge */
PreviousDeltaYSign = SIGNUM(VertexPtr[Length-1].Y - VertexPtr[0].Y);
i = 0;
while ((PreviousDeltaYSign == 0) && (i < (Length-1))) {
PreviousDeltaYSign = SIGNUM(VertexPtr[i].Y - VertexPtr[i+1].Y);
i++;
}
if (i == (Length-1)) return(1); /* polygon is a flat line */
if (i == (Length-1)) return(1); /* polygon is a flat line */
/* Now count Y reversals. Might miss one reversal, at the last vertex, but
because reversal counts must be even, being off by one isn't a problem */
do {
if ((DeltaYSign = SIGNUM(VertexPtr[i].Y - VertexPtr[i+1].Y))
!= 0) {
if (DeltaYSign != PreviousDeltaYSign) {
/* Switched Y direction; not vertical-monotone if
reversed Y direction as many as three times */
if (++NumYReversals > 2) return(0);
PreviousDeltaYSign = DeltaYSign;
}
}
} while (i++ < (Length-1));
return(1); /* it's a vertical-monotone polygon */
}
/* Now count Y reversals. Might miss one reversal, at the last vertex, but
because reversal counts must be even, being off by one isn't a problem */
do {
if ((DeltaYSign = SIGNUM(VertexPtr[i].Y - VertexPtr[i+1].Y))
!= 0) {
if (DeltaYSign != PreviousDeltaYSign) {
/* Switched Y direction; not vertical-monotone if
reversed Y direction as many as three times */
if (++NumYReversals > 2) return(0);
PreviousDeltaYSign = DeltaYSign;
}
}
} while (i++ < (Length-1));
return(1); /* it's a vertical-monotone polygon */
}
```