minor edits to d2map engine, added methods for converting between ind…

…ex and tile coordinates (OpenDiablo2#433)

d2core/d2map/d2mapengine/engine.go

@@ -137,28 +137,51 @@ func (m *MapEngine) Tiles() *[]d2ds1.TileRecord {
 	return &m.tiles
 }
 
-// Places a stamp at the specified location. Also adds any entities from the stamp to the map engine
+// Places a stamp at the specified location.
+// Also adds any entities from the stamp to the map engine
 func (m *MapEngine) PlaceStamp(stamp *d2mapstamp.Stamp, tileOffsetX, tileOffsetY int) {
 	stampSize := stamp.Size()
-	if (tileOffsetX < 0) || (tileOffsetY < 0) || ((tileOffsetX + stampSize.Width) > m.size.Width) || ((tileOffsetY + stampSize.Height) > m.size.Height) {
+	stampW := stampSize.Width
+	stampH := stampSize.Height
+
+	mapW := m.size.Width
+	mapH := m.size.Height
+
+	xMin := tileOffsetX
+	yMin := tileOffsetY
+	xMax := xMin + stampSize.Width
+	yMax := yMin + stampSize.Height
+
+	if (xMin < 0) || (yMin < 0) || (xMax > mapW) || (yMax > mapH) {
 		panic("Tried placing a stamp outside the bounds of the map")
 	}
 
 	// Copy over the map tile data
-	for y := 0; y < stampSize.Height; y++ {
-		for x := 0; x < stampSize.Width; x++ {
-			mapTileIdx := x + tileOffsetX + ((y + tileOffsetY) * m.size.Width)
-			m.tiles[mapTileIdx] = *stamp.Tile(x, y)
+	for y := 0; y < stampH; y++ {
+		for x := 0; x < stampW; x++ {
+			targetTileIndex := m.tileCoordinateToIndex((x + xMin), (y + yMin))
+			stampTile := *stamp.Tile(x, y)
+			m.tiles[targetTileIndex] = stampTile
 		}
 	}
 
 	// Copy over the entities
 	m.entities = append(m.entities, stamp.Entities(tileOffsetX, tileOffsetY)...)
 }
 
-// Returns a reference to a map tile based on the specified tile X and Y coordinate
+// converts x,y tile coordinate into index in MapEngine.tiles
+func (m *MapEngine) tileCoordinateToIndex(x, y int) int {
+	return x + (y * m.size.Height)
+}
+
+// converts tile index from MapEngine.tiles to x,y coordinate
+func (m *MapEngine) tileIndexToCoordinate(index int) (int, int) {
+	return (index % m.size.Width), (index / m.size.Width)
+}
+
+// Returns a reference to a map tile based on the tile X,Y coordinate
 func (m *MapEngine) TileAt(tileX, tileY int) *d2ds1.TileRecord {
-	idx := tileX + (tileY * m.size.Width)
+	idx := m.tileCoordinateToIndex(tileX, tileY)
 	if idx < 0 || idx >= len(m.tiles) {
 		return nil
 	}
@@ -231,12 +254,18 @@ func (m *MapEngine) Advance(tickTime float64) {
 	}
 }
 
+// Checks if a tile exists
 func (m *MapEngine) TileExists(tileX, tileY int) bool {
-	if tileX < 0 || tileX >= m.size.Width || tileY < 0 || tileY >= m.size.Height {
-		return false
+	tileIndex := m.tileCoordinateToIndex(tileX, tileY)
+	if valid := (tileIndex >= 0) && (tileIndex <= len(m.tiles)); valid {
+		tile := m.tiles[tileIndex]
+		numFeatures := len(tile.Floors)
+		numFeatures += len(tile.Shadows)
+		numFeatures += len(tile.Walls)
+		numFeatures += len(tile.Substitutions)
+		return numFeatures > 0
 	}
-	tile := m.tiles[tileX+(tileY*m.size.Width)]
-	return len(tile.Floors) > 0 || len(tile.Shadows) > 0 || len(tile.Walls) > 0 || len(tile.Substitutions) > 0
+	return false
 }
 
 func (m *MapEngine) GenerateMap(regionType d2enum.RegionIdType, levelPreset int, fileIndex int, cacheTiles bool) {