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James Gregory 2013-12-30 18:34:31 +11:00
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41-02.md
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@ -16,13 +16,13 @@ from Chapter 39) remains the same, and so is not shown again here.
**LISTING 41.2 L41-2.C**
/* Color-fills a convex polygon. All vertices are offset by (XOffset, YOffset).
“Convex” means “monotone with respect to a vertical line”; that is, every
"Convex" means "monotone with respect to a vertical line"; that is, every
horizontal line drawn through the polygon at any point would cross exactly two
active edges (neither horizontal lines nor zero-length edges count as active
edges; both are acceptable anywhere in the polygon). Right & left edges may
cross (polygons may be nonsimple). Polygons that are not convex according to
this definition won’t be drawn properly. (Yes, “convex” is a lousy name for
this type of polygon, but it’s convenient; use “monotone-vertical” if it makes
this definition won't be drawn properly. (Yes, "convex" is a lousy name for
this type of polygon, but it's convenient; use "monotone-vertical" if it makes
you happier!)
*******************************************************************
NOTE: the low-level drawing routine, DrawHorizontalLineList, must be able to
@ -31,14 +31,14 @@ from Chapter 39) remains the same, and so is not shown again here.
highest coordinate to draw). In both respects, this differs from low-level
drawing routines presented in earlier columns; changes are necessary to make it
possible to draw nonsimple monotone-vertical polygons; that in turn makes it
possible to use Jim Kent’s test for monotone-vertical polygons.
possible to use Jim Kent's test for monotone-vertical polygons.
*******************************************************************
Returns 1 for success, 0 if memory allocation failed */
#include <stdio.h>
#include <math.h>
#include <stdlib.h>
#include “polygon.h”
#include "polygon.h"
/* Advances the index by one vertex forward through the vertex list,
wrapping at the end of the list */
@ -86,14 +86,14 @@ from Chapter 39) remains the same, and so is not shown again here.
/* Set the # of scan lines in the polygon, skipping the bottom edge */
if ((WorkingHLineList.Length = MaxPoint_Y - MinPoint_Y) <= 0)
return(1); /* there’s nothing to draw, so we’re done */
return(1); /* there's nothing to draw, so we're done */
WorkingHLineList.YStart = YOffset + MinPoint_Y;
/* Get memory in which to store the line list we generate */
if ((WorkingHLineList.HLinePtr =
(struct HLine *) (malloc(sizeof(struct HLine) *
WorkingHLineList.Length))) == NULL)
return(0); /* couldn’t get memory for the line list */
return(0); /* couldn't get memory for the line list */
/* Scan the first edge and store the boundary points in the list */
/* Initial pointer for storing scan converted first-edge coords */
@ -126,7 +126,7 @@ from Chapter 39) remains the same, and so is not shown again here.
/* Draw the line list representing the scan converted polygon */
DrawHorizontalLineList(&WorkingHLineList, Color);
/* Release the line list’s memory and we’re successfully done */
/* Release the line list's memory and we're successfully done */
free(WorkingHLineList.HLinePtr);
return(1);
}