ui: basic map scroller

client/world/renderer_query.go

@@ -0,0 +1,80 @@
+package world
+
+import (
+	"errors"
+
+	"github.com/google/uuid"
+)
+
+var (
+	errGridNotBuilt = errors.New("render: grid not built; call IndexOnViewportChange first")
+)
+
+// TileCandidates binds one torus tile to the list of unique grid candidates
+// that intersect the tile rectangle.
+//
+// Items are not guaranteed to be truly visible; the grid is a coarse spatial index.
+// Exact visibility tests are performed later in the renderer pipeline.
+type TileCandidates struct {
+	Tile  WorldTile
+	Items []MapItem
+}
+
+// collectCandidatesForTiles queries the world grid for each tile rectangle
+// and returns per-tile unique candidate lists.
+//
+// Deduplication is performed per tile (by MapItem.ID()) to avoid duplicates caused by
+// bbox indexing into multiple cells. Dedup across tiles is intentionally NOT performed.
+func (w *World) collectCandidatesForTiles(tiles []WorldTile) ([]TileCandidates, error) {
+	if w.grid == nil || w.rows <= 0 || w.cols <= 0 || w.cellSize <= 0 {
+		return nil, errGridNotBuilt
+	}
+
+	out := make([]TileCandidates, 0, len(tiles))
+	for _, tile := range tiles {
+		items := w.collectCandidatesForTile(tile.Rect)
+		out = append(out, TileCandidates{
+			Tile:  tile,
+			Items: items,
+		})
+	}
+	return out, nil
+}
+
+// collectCandidatesForTile returns a unique set of grid candidates for a single
+// canonical-world tile rectangle [0..W) x [0..H).
+//
+// The rectangle must be half-open and expressed in fixed-point world coordinates.
+func (w *World) collectCandidatesForTile(r Rect) []MapItem {
+	// Empty rect => no candidates.
+	if r.maxX <= r.minX || r.maxY <= r.minY {
+		return nil
+	}
+
+	// Map rect to cell ranges using the same half-open conventions as indexing:
+	// the last included cell is computed from (max-1).
+	colStart := w.worldToCellX(r.minX)
+	colEnd := w.worldToCellX(r.maxX - 1)
+
+	rowStart := w.worldToCellY(r.minY)
+	rowEnd := w.worldToCellY(r.maxY - 1)
+
+	seen := make(map[uuid.UUID]struct{})
+	result := make([]MapItem, 0)
+
+	for row := rowStart; row <= rowEnd; row++ {
+		for col := colStart; col <= colEnd; col++ {
+			cell := w.grid[row][col]
+			for _, item := range cell {
+				id := item.ID()
+				if _, ok := seen[id]; ok {
+					continue
+				}
+				seen[id] = struct{}{}
+				result = append(result, item)
+			}
+		}
+	}
+
+	return result
+}