[FEAT] add grid metrics

src/components/SpriteCanvas.vue

@@ -204,6 +204,8 @@
   import type { Sprite } from '@/types/sprites';
   import { useDragSprite } from '@/composables/useDragSprite';
   import { useFileDrop } from '@/composables/useFileDrop';
+  import { useGridMetrics } from '@/composables/useGridMetrics';
+  import { useBackgroundStyles } from '@/composables/useBackgroundStyles';
 
   import type { Layer } from '@/types/sprites';
 
@@ -315,8 +317,16 @@
     }
   );
 
-  // Grid metrics
-  const gridMetrics = computed(() => calculateMaxDimensions());
+  // Use the new useGridMetrics composable for consistent calculations
+  const { gridMetrics: gridMetricsRef, getCellPosition: getCellPositionHelper } = useGridMetrics({
+    layers: toRef(props, 'layers'),
+    negativeSpacingEnabled: toRef(settingsStore, 'negativeSpacingEnabled'),
+    manualCellSizeEnabled: toRef(settingsStore, 'manualCellSizeEnabled'),
+    manualCellWidth: toRef(settingsStore, 'manualCellWidth'),
+    manualCellHeight: toRef(settingsStore, 'manualCellHeight'),
+  });
+
+  const gridMetrics = gridMetricsRef;
 
   const totalCells = computed(() => {
     // Use all layers regardless of visibility to keep canvas size stable
@@ -335,47 +345,20 @@
   });
 
   const getCellPosition = (index: number) => {
-    const col = index % props.columns;
-    const row = Math.floor(index / props.columns);
-    return {
-      x: Math.round(col * gridMetrics.value.maxWidth),
-      y: Math.round(row * gridMetrics.value.maxHeight),
-    };
+    return getCellPositionHelper(index, props.columns, gridMetrics.value);
   };
 
-  const getCellBackground = () => {
-    const bg = settingsStore.backgroundColor;
-    if (bg === 'transparent') {
-      return 'transparent';
-    }
-    return bg;
-  };
+  // Use the new useBackgroundStyles composable for consistent background styling
+  const { backgroundColor: cellBackgroundColor, backgroundImage: cellBackgroundImage, backgroundSize: cellBackgroundSize, backgroundPosition: cellBackgroundPosition } = useBackgroundStyles({
+    backgroundColor: toRef(settingsStore, 'backgroundColor'),
+    checkerboardEnabled: toRef(settingsStore, 'checkerboardEnabled'),
+    darkMode: toRef(settingsStore, 'darkMode'),
+  });
 
-  const getCellBackgroundImage = () => {
-    const bg = settingsStore.backgroundColor;
-    if (bg === 'transparent' && settingsStore.checkerboardEnabled) {
-      // Checkerboard pattern for transparent backgrounds (dark mode friendly)
-      const color = settingsStore.darkMode ? '#4b5563' : '#d1d5db';
-      return `linear-gradient(45deg, ${color} 25%, transparent 25%), linear-gradient(-45deg, ${color} 25%, transparent 25%), linear-gradient(45deg, transparent 75%, ${color} 75%), linear-gradient(-45deg, transparent 75%, ${color} 75%)`;
-    }
-    return 'none';
-  };
-
-  const getCellBackgroundSize = () => {
-    const bg = settingsStore.backgroundColor;
-    if (bg === 'transparent') {
-      return '20px 20px';
-    }
-    return 'auto';
-  };
-
-  const getCellBackgroundPosition = () => {
-    const bg = settingsStore.backgroundColor;
-    if (bg === 'transparent') {
-      return '0 0, 0 10px, 10px -10px, -10px 0px';
-    }
-    return '0 0';
-  };
+  const getCellBackground = () => cellBackgroundColor.value;
+  const getCellBackgroundImage = () => cellBackgroundImage.value;
+  const getCellBackgroundSize = () => cellBackgroundSize.value;
+  const getCellBackgroundPosition = () => cellBackgroundPosition.value;
 
   const startDrag = (event: MouseEvent) => {
     // If the click originated from an interactive element (button, link, input), ignore drag handling

src/components/SpritePreview.vue

@@ -73,9 +73,9 @@
               width: `${cellDimensions.cellWidth}px`,
               height: `${cellDimensions.cellHeight}px`,
               backgroundColor: settingsStore.backgroundColor === 'transparent' ? '#f9fafb' : settingsStore.backgroundColor,
-              backgroundImage: getPreviewBackgroundImage(),
-              backgroundSize: settingsStore.backgroundColor === 'transparent' ? '20px 20px' : 'auto',
-              backgroundPosition: settingsStore.backgroundColor === 'transparent' ? '0 0, 0 10px, 10px -10px, -10px 0px' : '0 0',
+              backgroundImage: previewBackgroundImage,
+              backgroundSize: previewBackgroundSize,
+              backgroundPosition: previewBackgroundPosition,
               border: `1px solid ${settingsStore.darkMode ? '#4b5563' : '#e5e7eb'}`,
             }"
             @dragover.prevent="onDragOver"
@@ -302,13 +302,13 @@
 </template>
 
 <script setup lang="ts">
-  import { ref, onMounted, watch, onUnmounted, computed } from 'vue';
+  import { ref, onMounted, watch, onUnmounted, computed, toRef } from 'vue';
   import { useSettingsStore } from '@/stores/useSettingsStore';
   import type { Layer, Sprite } from '@/types/sprites';
-  import { getMaxDimensionsAcrossLayers } from '@/composables/useLayers';
   import { useZoom } from '@/composables/useZoom';
   import { useAnimationFrames } from '@/composables/useAnimationFrames';
-  import { calculateNegativeSpacing } from '@/composables/useNegativeSpacing';
+  import { useGridMetrics } from '@/composables/useGridMetrics';
+  import { useBackgroundStyles } from '@/composables/useBackgroundStyles';
 
   const props = defineProps<{
     layers: Layer[];
@@ -426,38 +426,30 @@
     return layer.sprites[currentFrameIndex.value] || null;
   });
 
-  // Computed cell dimensions
-  const cellDimensions = computed(() => {
-    // Use ALL layers (regardless of visibility) to keep preview size stable
-    const allLayers = props.layers;
-    // If manual cell size is enabled, use manual values
-    if (settingsStore.manualCellSizeEnabled) {
-      return {
-        cellWidth: Math.round(settingsStore.manualCellWidth),
-        cellHeight: Math.round(settingsStore.manualCellHeight),
-        negativeSpacing: 0,
-      };
-    }
-
-    // Otherwise, calculate from sprite dimensions across ALL layers
-    const { maxWidth, maxHeight } = getMaxDimensionsAcrossLayers(allLayers);
-    const allSprites = allLayers.flatMap(l => l.sprites);
-    const negativeSpacing = Math.round(calculateNegativeSpacing(allSprites, settingsStore.negativeSpacingEnabled));
-    return {
-      cellWidth: Math.round(maxWidth + negativeSpacing),
-      cellHeight: Math.round(maxHeight + negativeSpacing),
-      negativeSpacing,
-    };
+  // Use the new useGridMetrics composable for consistent calculations
+  const { gridMetrics } = useGridMetrics({
+    layers: toRef(props, 'layers'),
+    negativeSpacingEnabled: toRef(settingsStore, 'negativeSpacingEnabled'),
+    manualCellSizeEnabled: toRef(settingsStore, 'manualCellSizeEnabled'),
+    manualCellWidth: toRef(settingsStore, 'manualCellWidth'),
+    manualCellHeight: toRef(settingsStore, 'manualCellHeight'),
   });
 
-  // Helper for background image (dark mode friendly)
-  const getPreviewBackgroundImage = () => {
-    if (settingsStore.backgroundColor === 'transparent' && settingsStore.checkerboardEnabled) {
-      const color = settingsStore.darkMode ? '#4b5563' : '#d1d5db';
-      return `linear-gradient(45deg, ${color} 25%, transparent 25%), linear-gradient(-45deg, ${color} 25%, transparent 25%), linear-gradient(45deg, transparent 75%, ${color} 75%), linear-gradient(-45deg, transparent 75%, ${color} 75%)`;
-    }
-    return 'none';
-  };
+  // Computed cell dimensions (for backward compatibility with existing code)
+  const cellDimensions = computed(() => ({
+    cellWidth: gridMetrics.value.maxWidth,
+    cellHeight: gridMetrics.value.maxHeight,
+    negativeSpacing: gridMetrics.value.negativeSpacing,
+  }));
+
+  // Use the new useBackgroundStyles composable for consistent background styling
+  const { backgroundImage: previewBackgroundImage, backgroundSize: previewBackgroundSize, backgroundPosition: previewBackgroundPosition } = useBackgroundStyles({
+    backgroundColor: toRef(settingsStore, 'backgroundColor'),
+    checkerboardEnabled: toRef(settingsStore, 'checkerboardEnabled'),
+    darkMode: toRef(settingsStore, 'darkMode'),
+  });
+
+  const getPreviewBackgroundImage = () => previewBackgroundImage.value;
 
   // Dragging state
   const isDragging = ref(false);

src/composables/useBackgroundStyles.ts

@@ -0,0 +1,113 @@
+import { computed, type Ref, type ComputedRef } from 'vue';
+
+export interface BackgroundStylesOptions {
+  backgroundColor: Ref<string> | ComputedRef<string> | string;
+  checkerboardEnabled?: Ref<boolean> | ComputedRef<boolean> | boolean;
+  darkMode?: Ref<boolean> | ComputedRef<boolean> | boolean;
+}
+
+export interface BackgroundStyles {
+  backgroundColor: string;
+  backgroundImage: string;
+  backgroundSize: string;
+  backgroundPosition: string;
+}
+
+/**
+ * Composable for generating consistent background styles across components.
+ * Handles transparent backgrounds with checkerboard patterns and dark mode.
+ */
+export function useBackgroundStyles(options: BackgroundStylesOptions) {
+  // Helper to get reactive values
+  const getBackgroundColor = () => (typeof options.backgroundColor === 'string' ? options.backgroundColor : options.backgroundColor.value);
+  const getCheckerboardEnabled = () => (typeof options.checkerboardEnabled === 'boolean' ? options.checkerboardEnabled : options.checkerboardEnabled?.value ?? true);
+  const getDarkMode = () => (typeof options.darkMode === 'boolean' ? options.darkMode : options.darkMode?.value ?? false);
+
+  /**
+   * Get the background color.
+   */
+  const backgroundColor = computed(() => {
+    const bg = getBackgroundColor();
+    return bg === 'transparent' ? 'transparent' : bg;
+  });
+
+  /**
+   * Get the background image (checkerboard pattern for transparent backgrounds).
+   */
+  const backgroundImage = computed(() => {
+    const bg = getBackgroundColor();
+    const checkerboardEnabled = getCheckerboardEnabled();
+    const darkMode = getDarkMode();
+
+    if (bg === 'transparent' && checkerboardEnabled) {
+      // Checkerboard pattern for transparent backgrounds (dark mode friendly)
+      const color = darkMode ? '#4b5563' : '#d1d5db';
+      return `linear-gradient(45deg, ${color} 25%, transparent 25%), linear-gradient(-45deg, ${color} 25%, transparent 25%), linear-gradient(45deg, transparent 75%, ${color} 75%), linear-gradient(-45deg, transparent 75%, ${color} 75%)`;
+    }
+    return 'none';
+  });
+
+  /**
+   * Get the background size.
+   */
+  const backgroundSize = computed(() => {
+    const bg = getBackgroundColor();
+    return bg === 'transparent' ? '20px 20px' : 'auto';
+  });
+
+  /**
+   * Get the background position.
+   */
+  const backgroundPosition = computed(() => {
+    const bg = getBackgroundColor();
+    return bg === 'transparent' ? '0 0, 0 10px, 10px -10px, -10px 0px' : '0 0';
+  });
+
+  /**
+   * Get all background styles as a single object.
+   */
+  const backgroundStyles = computed<BackgroundStyles>(() => ({
+    backgroundColor: backgroundColor.value,
+    backgroundImage: backgroundImage.value,
+    backgroundSize: backgroundSize.value,
+    backgroundPosition: backgroundPosition.value,
+  }));
+
+  return {
+    backgroundColor,
+    backgroundImage,
+    backgroundSize,
+    backgroundPosition,
+    backgroundStyles,
+  };
+}
+
+/**
+ * Standalone helper to get background styles.
+ * Useful when you don't need the full composable.
+ */
+export function getBackgroundStyles(
+  backgroundColor: string,
+  options: {
+    checkerboardEnabled?: boolean;
+    darkMode?: boolean;
+  } = {}
+): BackgroundStyles {
+  const checkerboardEnabled = options.checkerboardEnabled ?? true;
+  const darkMode = options.darkMode ?? false;
+
+  const bg = backgroundColor === 'transparent' ? 'transparent' : backgroundColor;
+
+  let bgImage = 'none';
+  if (backgroundColor === 'transparent' && checkerboardEnabled) {
+    const color = darkMode ? '#4b5563' : '#d1d5db';
+    bgImage = `linear-gradient(45deg, ${color} 25%, transparent 25%), linear-gradient(-45deg, ${color} 25%, transparent 25%), linear-gradient(45deg, transparent 75%, ${color} 75%), linear-gradient(-45deg, transparent 75%, ${color} 75%)`;
+  }
+
+  return {
+    backgroundColor: bg,
+    backgroundImage: bgImage,
+    backgroundSize: backgroundColor === 'transparent' ? '20px 20px' : 'auto',
+    backgroundPosition: backgroundColor === 'transparent' ? '0 0, 0 10px, 10px -10px, -10px 0px' : '0 0',
+  };
+}

src/composables/useDragSprite.ts

@@ -1,7 +1,6 @@
 import { ref, computed, type Ref, type ComputedRef } from 'vue';
 import type { Sprite, Layer } from '@/types/sprites';
-import { getMaxDimensions } from './useSprites';
-import { calculateNegativeSpacing } from './useNegativeSpacing';
+import { useGridMetrics, type GridMetrics } from './useGridMetrics';
 
 export interface CellPosition {
   col: number;
@@ -70,70 +69,42 @@ export function useDragSprite(options: DragSpriteOptions) {
   const ghostSprite = ref<{ id: string; x: number; y: number } | null>(null);
   const highlightCell = ref<CellPosition | null>(null);
 
-  // Cache for max dimensions
-  const lastMaxWidth = ref(1);
-  const lastMaxHeight = ref(1);
+  // Use the new useGridMetrics composable for consistent calculations
+  const gridMetricsComposable = useGridMetrics({
+    layers: options.layers,
+    sprites: options.sprites,
+    negativeSpacingEnabled: options.negativeSpacingEnabled,
+    manualCellSizeEnabled: options.manualCellSizeEnabled,
+    manualCellWidth: options.manualCellWidth,
+    manualCellHeight: options.manualCellHeight,
+  });
 
-  const calculateMaxDimensions = () => {
-    const negativeSpacingEnabled = getNegativeSpacingEnabled();
-    const manualCellSizeEnabled = getManualCellSizeEnabled();
-
-    // If manual cell size is enabled, use manual dimensions
-    if (manualCellSizeEnabled) {
-      const maxWidth = getManualCellWidth();
-      const maxHeight = getManualCellHeight();
-      // When manual cell size is used, negative spacing is not applied
-      const negativeSpacing = 0;
-      // Don't update lastMaxWidth/lastMaxHeight when in manual mode
-      return { maxWidth, maxHeight, negativeSpacing };
-    }
-
-    // Get all sprites to calculate dimensions from
-    // If layers are provided, use ALL layers (regardless of visibility) to keep canvas size stable
-    const layers = getLayers();
-    const spritesToMeasure = layers ? layers.flatMap(l => l.sprites) : getSprites();
-
-    // Otherwise, calculate based on sprite dimensions across all visible layers
-    const base = getMaxDimensions(spritesToMeasure);
-    // When switching back from manual mode, reset to actual sprite dimensions
-    const baseMaxWidth = Math.max(1, base.maxWidth);
-    const baseMaxHeight = Math.max(1, base.maxHeight);
-    lastMaxWidth.value = baseMaxWidth;
-    lastMaxHeight.value = baseMaxHeight;
-
-    // Calculate negative spacing using shared composable
-    const negativeSpacing = Math.round(calculateNegativeSpacing(spritesToMeasure, negativeSpacingEnabled));
-
-    // Add negative spacing to expand each cell
-    const maxWidth = Math.round(baseMaxWidth + negativeSpacing);
-    const maxHeight = Math.round(baseMaxHeight + negativeSpacing);
-    return { maxWidth, maxHeight, negativeSpacing };
+  const calculateMaxDimensions = (): GridMetrics => {
+    return gridMetricsComposable.calculateCellDimensions();
   };
 
   // Computed sprite positions
   const spritePositions = computed<SpritePosition[]>(() => {
     const sprites = getSprites();
     const columns = getColumns();
-    const { maxWidth, maxHeight, negativeSpacing } = calculateMaxDimensions();
+    const metrics = calculateMaxDimensions();
 
     return sprites.map((sprite, index) => {
-      const col = index % columns;
-      const row = Math.floor(index / columns);
+      const cellPos = gridMetricsComposable.getCellPosition(index, columns, metrics);
+      const canvasPos = gridMetricsComposable.getSpriteCanvasPosition(sprite, index, columns, metrics);
 
-      // With negative spacing, sprites are positioned at bottom-right of cell
-      // (spacing added to top and left)
       return {
         id: sprite.id,
-        canvasX: Math.round(col * maxWidth + negativeSpacing + sprite.x),
-        canvasY: Math.round(row * maxHeight + negativeSpacing + sprite.y),
-        cellX: Math.round(col * maxWidth),
-        cellY: Math.round(row * maxHeight),
+        canvasX: canvasPos.canvasX,
+        canvasY: canvasPos.canvasY,
+        cellX: canvasPos.cellX,
+        cellY: canvasPos.cellY,
         width: Math.round(sprite.width),
         height: Math.round(sprite.height),
-        maxWidth: Math.round(maxWidth),
-        maxHeight: Math.round(maxHeight),
-        col,
-        row,
+        maxWidth: metrics.maxWidth,
+        maxHeight: metrics.maxHeight,
+        col: cellPos.col,
+        row: cellPos.row,
         index,
         x: sprite.x,
         y: sprite.y,

src/composables/useGridMetrics.ts

@@ -0,0 +1,165 @@
+import { computed, type Ref, type ComputedRef } from 'vue';
+import type { Sprite, Layer } from '@/types/sprites';
+import { getMaxDimensions } from './useSprites';
+import { calculateNegativeSpacing } from './useNegativeSpacing';
+
+export interface GridMetrics {
+  maxWidth: number;
+  maxHeight: number;
+  negativeSpacing: number;
+}
+
+export interface CellPosition {
+  x: number;
+  y: number;
+  col: number;
+  row: number;
+}
+
+export interface SpriteCanvasPosition {
+  canvasX: number;
+  canvasY: number;
+  cellX: number;
+  cellY: number;
+}
+
+export interface GridMetricsOptions {
+  layers?: Ref<Layer[]> | ComputedRef<Layer[]> | Layer[];
+  sprites?: Ref<Sprite[]> | ComputedRef<Sprite[]> | Sprite[];
+  negativeSpacingEnabled?: Ref<boolean> | boolean;
+  manualCellSizeEnabled?: Ref<boolean> | boolean;
+  manualCellWidth?: Ref<number> | number;
+  manualCellHeight?: Ref<number> | number;
+}
+
+/**
+ * Composable for calculating grid metrics and sprite positions.
+ * Provides a single source of truth for cell dimensions and positioning calculations.
+ */
+export function useGridMetrics(options: GridMetricsOptions = {}) {
+  // Helper to get reactive values
+  const getLayers = () => (options.layers ? (Array.isArray(options.layers) ? options.layers : options.layers.value) : null);
+  const getSprites = () => (options.sprites ? (Array.isArray(options.sprites) ? options.sprites : options.sprites.value) : []);
+  const getNegativeSpacingEnabled = () => (typeof options.negativeSpacingEnabled === 'boolean' ? options.negativeSpacingEnabled : options.negativeSpacingEnabled?.value ?? false);
+  const getManualCellSizeEnabled = () => (typeof options.manualCellSizeEnabled === 'boolean' ? options.manualCellSizeEnabled : options.manualCellSizeEnabled?.value ?? false);
+  const getManualCellWidth = () => (typeof options.manualCellWidth === 'number' ? options.manualCellWidth : options.manualCellWidth?.value ?? 64);
+  const getManualCellHeight = () => (typeof options.manualCellHeight === 'number' ? options.manualCellHeight : options.manualCellHeight?.value ?? 64);
+
+  /**
+   * Calculate cell dimensions including negative spacing.
+   * This is the canonical calculation used across all components.
+   */
+  const calculateCellDimensions = (): GridMetrics => {
+    const manualCellSizeEnabled = getManualCellSizeEnabled();
+
+    // If manual cell size is enabled, use manual dimensions
+    if (manualCellSizeEnabled) {
+      return {
+        maxWidth: Math.round(getManualCellWidth()),
+        maxHeight: Math.round(getManualCellHeight()),
+        negativeSpacing: 0,
+      };
+    }
+
+    // Get sprites to measure from layers or direct sprites array
+    const layers = getLayers();
+    const spritesToMeasure = layers ? layers.flatMap(l => l.sprites) : getSprites();
+
+    // Calculate base dimensions from sprites
+    const base = getMaxDimensions(spritesToMeasure);
+    const baseMaxWidth = Math.max(1, base.maxWidth);
+    const baseMaxHeight = Math.max(1, base.maxHeight);
+
+    // Calculate negative spacing
+    const negativeSpacingEnabled = getNegativeSpacingEnabled();
+    const negativeSpacing = Math.round(calculateNegativeSpacing(spritesToMeasure, negativeSpacingEnabled));
+
+    // Add negative spacing to expand each cell
+    return {
+      maxWidth: Math.round(baseMaxWidth + negativeSpacing),
+      maxHeight: Math.round(baseMaxHeight + negativeSpacing),
+      negativeSpacing,
+    };
+  };
+
+  /**
+   * Get the position of a cell in the grid.
+   */
+  const getCellPosition = (index: number, columns: number, metrics: GridMetrics): CellPosition => {
+    const col = index % columns;
+    const row = Math.floor(index / columns);
+    return {
+      x: Math.round(col * metrics.maxWidth),
+      y: Math.round(row * metrics.maxHeight),
+      col,
+      row,
+    };
+  };
+
+  /**
+   * Get the canvas position of a sprite within a cell.
+   * This is the final position where the sprite should be rendered.
+   */
+  const getSpriteCanvasPosition = (sprite: Sprite, cellIndex: number, columns: number, metrics: GridMetrics): SpriteCanvasPosition => {
+    const cellPos = getCellPosition(cellIndex, columns, metrics);
+    return {
+      canvasX: Math.round(cellPos.x + metrics.negativeSpacing + sprite.x),
+      canvasY: Math.round(cellPos.y + metrics.negativeSpacing + sprite.y),
+      cellX: cellPos.x,
+      cellY: cellPos.y,
+    };
+  };
+
+  /**
+   * Computed grid metrics that automatically updates when dependencies change.
+   */
+  const gridMetrics = computed(() => calculateCellDimensions());
+
+  return {
+    // Computed values
+    gridMetrics,
+
+    // Methods
+    calculateCellDimensions,
+    getCellPosition,
+    getSpriteCanvasPosition,
+  };
+}
+
+/**
+ * Standalone helper to calculate cell dimensions.
+ * Useful when you don't need the full composable.
+ */
+export function getGridMetrics(
+  spritesOrLayers: Sprite[] | Layer[],
+  options: {
+    negativeSpacingEnabled?: boolean;
+    manualCellSizeEnabled?: boolean;
+    manualCellWidth?: number;
+    manualCellHeight?: number;
+  } = {}
+): GridMetrics {
+  if (options.manualCellSizeEnabled) {
+    return {
+      maxWidth: Math.round(options.manualCellWidth ?? 64),
+      maxHeight: Math.round(options.manualCellHeight ?? 64),
+      negativeSpacing: 0,
+    };
+  }
+
+  // Check if we have layers or sprites
+  const isLayers = spritesOrLayers.length > 0 && 'sprites' in spritesOrLayers[0];
+  const sprites = isLayers ? (spritesOrLayers as Layer[]).flatMap(l => l.sprites) : (spritesOrLayers as Sprite[]);
+
+  const base = getMaxDimensions(sprites);
+  const baseMaxWidth = Math.max(1, base.maxWidth);
+  const baseMaxHeight = Math.max(1, base.maxHeight);
+
+  const negativeSpacing = Math.round(calculateNegativeSpacing(sprites, options.negativeSpacingEnabled ?? false));
+
+  return {
+    maxWidth: Math.round(baseMaxWidth + negativeSpacing),
+    maxHeight: Math.round(baseMaxHeight + negativeSpacing),
+    negativeSpacing,
+  };
+}