static void
CreateETandAET(
register int count,
register XPoint *pts,
EdgeTable *ET,
EdgeTableEntry *AET,
register EdgeTableEntry *pETEs,
ScanLineListBlock *pSLLBlock)
{
register XPoint *top, *bottom;
register XPoint *PrevPt, *CurrPt;
int iSLLBlock = 0;
int dy;
if (count < 2) return;
/*
* initialize the Active Edge Table
*/
AET->next = (EdgeTableEntry *)NULL;
AET->back = (EdgeTableEntry *)NULL;
AET->nextWETE = (EdgeTableEntry *)NULL;
AET->bres.minor_axis = SMALL_COORDINATE;
/*
* initialize the Edge Table.
*/
ET->scanlines.next = (ScanLineList *)NULL;
ET->ymax = SMALL_COORDINATE;
ET->ymin = LARGE_COORDINATE;
pSLLBlock->next = (ScanLineListBlock *)NULL;
PrevPt = &pts[count-1];
/*
* for each vertex in the array of points.
* In this loop we are dealing with two vertices at
* a time -- these make up one edge of the polygon.
*/
while (count--)
{
CurrPt = pts++;
/*
* find out which point is above and which is below.
*/
if (PrevPt->y > CurrPt->y)
{
bottom = PrevPt, top = CurrPt;
pETEs->ClockWise = 0;
}
else
{
bottom = CurrPt, top = PrevPt;
pETEs->ClockWise = 1;
}
/*
* don't add horizontal edges to the Edge table.
*/
if (bottom->y != top->y)
{
pETEs->ymax = bottom->y-1; /* -1 so we don't get last scanline */
/*
* initialize integer edge algorithm
*/
dy = bottom->y - top->y;
BRESINITPGONSTRUCT(dy, top->x, bottom->x, pETEs->bres);
InsertEdgeInET(ET, pETEs, top->y, &pSLLBlock, &iSLLBlock);
if (PrevPt->y > ET->ymax)
ET->ymax = PrevPt->y;
if (PrevPt->y < ET->ymin)
ET->ymin = PrevPt->y;
pETEs++;
}
PrevPt = CurrPt;
}
}
//______________________________________________________________________________
static void CreateETandAET(int count, TPoint *pts, EdgeTable *ET, EdgeTableEntry *AET,
EdgeTableEntry *pETEs, ScanLineListBlock *pSLLBlock)
{
// This routine creates the edge table for
// scan converting polygons.
// The Edge Table (ET) looks like:
//
// EdgeTable
// --------
// | ymax | ScanLineLists
// |scanline|-->------------>-------------->...
// -------- |scanline| |scanline|
// |edgelist| |edgelist|
// --------- ---------
// | |
// | |
// V V
// list of ETEs list of ETEs
//
// where ETE is an EdgeTableEntry data structure,
// and there is one ScanLineList per scanline at
// which an edge is initially entered.
TPoint *top, *bottom;
TPoint *PrevPt, *CurrPt;
int iSLLBlock = 0;
int dy;
if (count < 2) return;
/*
* initialize the Active Edge Table
*/
AET->next = (EdgeTableEntry *)0;
AET->back = (EdgeTableEntry *)0;
AET->nextWETE = (EdgeTableEntry *)0;
AET->bres.minor_axis = SMALL_COORDINATE;
/*
* initialize the Edge Table.
*/
ET->scanlines.next = (ScanLineList *)0;
ET->ymax = SMALL_COORDINATE;
ET->ymin = LARGE_COORDINATE;
pSLLBlock->next = (ScanLineListBlock *)0;
PrevPt = &pts[count-1];
/*
* for each vertex in the array of points.
* In this loop we are dealing with two vertices at
* a time -- these make up one edge of the polygon.
*/
while (count--) {
CurrPt = pts++;
/*
* find out which point is above and which is below.
*/
if (PrevPt->fY > CurrPt->fY) {
bottom = PrevPt, top = CurrPt;
pETEs->ClockWise = 0;
} else {
bottom = CurrPt, top = PrevPt;
pETEs->ClockWise = 1;
}
/*
* don't add horizontal edges to the Edge table.
*/
if (bottom->fY != top->fY) {
pETEs->ymax = bottom->fY-1; /* -1 so we don't get last scanline */
/*
* initialize integer edge algorithm
*/
dy = bottom->fY - top->fY;
BRESINITPGONSTRUCT(dy, top->fX, bottom->fX, pETEs->bres);
InsertEdgeInET(ET, pETEs, top->fY, &pSLLBlock, &iSLLBlock);
if (PrevPt->fY > ET->ymax) ET->ymax = PrevPt->fY;
if (PrevPt->fY < ET->ymin) ET->ymin = PrevPt->fY;
pETEs++;
}
PrevPt = CurrPt;
}
}