struct PointList* FillPolygon(struct PointListHeader * VertexList, int Color,
int PolygonShape, int XOffset, int YOffset)
{
struct EdgeState *EdgeTableBuffer;
int CurrentY;
InitDraw(); // inits point list that will be "drawn" (added) to the list
#ifdef CONVEX_CODE_LINKED
/* Pass convex polygons through to fast convex polygon filler */
if (PolygonShape == CONVEX)
return(FillConvexPolygon(VertexList, Color, XOffset, YOffset));
#endif
/* It takes a minimum of 3 vertices to cause any pixels to be
drawn; reject polygons that are guaranteed to be invisible */
if (VertexList->Length < 3)
return(0);
/* Get enough memory to store the entire edge table */
if ((EdgeTableBuffer =
(struct EdgeState *) (malloc(sizeof(struct EdgeState) *
VertexList->Length))) == NULL)
return(0); /* couldn't get memory for the edge table */
/* Build the global edge table */
BuildGET(VertexList, EdgeTableBuffer, XOffset, YOffset);
/* Scan down through the polygon edges, one scan line at a time,
so long as at least one edge remains in either the GET or AET */
AETPtr = NULL; /* initialize the active edge table to empty */
CurrentY = GETPtr->StartY; /* start at the top polygon vertex */
while ((GETPtr != NULL) || (AETPtr != NULL)) {
MoveXSortedToAET(CurrentY); /* update AET for this scan line */
ScanOutAET(CurrentY, Color); /* draw this scan line from AET */
AdvanceAET(); /* advance AET edges 1 scan line */
XSortAET(); /* resort on X */
CurrentY++; /* advance to the next scan line */
}
/* Release the memory we've allocated and we're done */
free(EdgeTableBuffer);
return(pointListTop);
}
int CreateScanLinesFromPolygon (int iVertexCount, SPoint *pVertexList, CG16bitRegion::SRun **retpLines)
// CreateScanLinesFromPolygon
//
// Creates a new array of scanlines from the given polygon. Returns the number of scanlines
// in the array. The caller is responsible for freeing the newly allocated array.
//
// NOTE: This function is NOT thread-safe--it must never be called from more than one
// thread simultaneously.
//
// Michael Abrash. Graphics Programming Black Book. Chapter 40.
{
// Reject polycons that have less then 3 vertices
if (iVertexCount < 3)
return 0;
// Initialize the output
g_iRunAlloc = INIT_ARRAY_ALLOC;
g_pRuns = new CG16bitRegion::SRun [g_iRunAlloc];
g_iRunCount = 0;
// Build the global edge table. This initializes g_pGET.
SEdgeState *EdgeTableBuffer = new SEdgeState [iVertexCount];
BuildGlobalEdgeTable(iVertexCount, pVertexList, EdgeTableBuffer);
// Active Edge Table is empty
g_pAET = NULL;
// Start at the top polygon vertex
int yCurrent = g_pGET->yStart;
// Scan down through the polygon edges, one scan line at a time,
// so long as at least one edge remains in either the GET or AET
while ((g_pGET != NULL) || (g_pAET != NULL))
{
// Update AET for this scan line
MoveXSortedToAET(yCurrent);
// Add to lines
ScanOutAET(yCurrent);
// Advance AET edges 1 scan line
AdvanceAET();
// Resort on X
XSortAET();
// Next
yCurrent++;
}
// Done
if (g_iRunCount > 0)
*retpLines = g_pRuns;
else
delete [] g_pRuns;
return g_iRunCount;
}