Add new Rectangle.grid with cell size argument (#223)

orx-shapes/src/commonMain/kotlin/RectangleGrid.kt

@@ -18,26 +18,62 @@ fun Rectangle.grid(
     marginY: Double = 0.0,
     gutterX: Double = 0.0,
     gutterY: Double = 0.0
+) = grid(
+    (width - marginX * 2 - gutterX * (columns - 1)) / columns,
+    (height - marginY * 2 - gutterY * (rows - 1)) / rows,
+    marginX, marginY,
+    gutterX, gutterY
+)
+
+/**
+ * Splits [Rectangle] into a grid of [Rectangle]s
+ * @param cellWidth the unitless width of a cell
+ * @param cellHeight the unitless height of a cell
+ * @param minMarginX the unitless minimum margin width (may increase to produce
+ * the desired cell aspect ratio)
+ * @param minMarginY the unitless minimum margin height (may increase to produce
+ * the desired cell aspect ratio)
+ * @param gutterX the unitless gutter width, the horizontal space between grid cells
+ * @param gutterY the unitless gutter height, the vertical space between grid cells
+ */
+fun Rectangle.grid(
+    cellWidth: Double,
+    cellHeight: Double,
+    minMarginX: Double = 0.0,
+    minMarginY: Double = 0.0,
+    gutterX: Double = 0.0,
+    gutterY: Double = 0.0
 ): List<List<Rectangle>> {
 
-    val totalWidth = width - marginX * 2.0
-    val totalHeight = height - marginY * 2.0
-
-    val totalGutterWidth = gutterX * (columns - 1).coerceAtLeast(0)
-    val totalGutterHeight = gutterY * (rows - 1).coerceAtLeast(0)
-
-    val cellWidth = ((totalWidth - totalGutterWidth) / columns).coerceAtLeast(0.0)
-    val cellHeight = ((totalHeight - totalGutterHeight) / rows).coerceAtLeast(0.0)
+    val availableWidth = (width - minMarginX * 2).coerceAtLeast(0.0)
+    val availableHeight = (height - minMarginY * 2).coerceAtLeast(0.0)
 
     val cellSpaceX = cellWidth + gutterX
     val cellSpaceY = cellHeight + gutterY
 
-    val x0 = x + marginX
-    val y0 = y + marginY
+    val columns = ((availableWidth + gutterX) / cellSpaceX).toInt()
+    val rows = ((availableHeight + gutterY) / cellSpaceY).toInt()
+
+    if (columns == 0 || rows == 0) {
+        return emptyList()
+    }
+
+    val totalGutterWidth = gutterX * (columns - 1).coerceAtLeast(0)
+    val totalGutterHeight = gutterY * (rows - 1).coerceAtLeast(0)
+
+    val totalWidth = cellWidth * columns + totalGutterWidth
+    val totalHeight = cellHeight * rows + totalGutterHeight
+
+    val x0 = x + (width - totalWidth) / 2
+    val y0 = y + (height - totalHeight) / 2
 
     return (0 until rows).map { row ->
         (0 until columns).map { column ->
-            Rectangle(x0 + column * cellSpaceX, y0 + row * cellSpaceY, cellWidth, cellHeight)
+            Rectangle(
+                x0 + column * cellSpaceX,
+                y0 + row * cellSpaceY,
+                cellWidth, cellHeight
+            )
         }
     }
-}
+}