diff --git a/example.cpp b/example.cpp
index 9aae1c6..f8d5139 100644
--- a/example.cpp
+++ b/example.cpp
@@ -861,7 +861,7 @@ void build_columndemo(int parent) {
     }
 }
 
-void fill_wrap_box(int box) {
+void fill_wrap_row_box(int box) {
     const int M = 5;
     const int S = 100;
     const int T = 50;
@@ -877,7 +877,7 @@ void fill_wrap_box(int box) {
             demorect(box, "Layout( UI_TOP )", hue, 0, UI_TOP, width, T, M, M, M, M);
         } break;
         case 1: {
-            demorect(box, "Layout( UI_VCENTER )", hue, 0, UI_VCENTER, width, T/2, M, 0, M, 0);
+            demorect(box, "Layout( UI_VCENTER )", hue, 0, UI_VCENTER, width, T/2, M, M, M, M);
         } break;
         case 2: {
             demorect(box, "Layout( UI_VFILL )", hue, 0, UI_VFILL, width, T, M, M, M, M);
@@ -890,11 +890,40 @@ void fill_wrap_box(int box) {
 
 }
 
+void fill_wrap_column_box(int box) {
+    const int M = 5;
+    const int S = 100;
+    const int T = 50;
+
+    srand(303);
+    for (int i = 0; i < 20; ++i) {
+        float hue = (float)(rand()%360)/360.0f;
+        int height = 10 + (rand()%5)*10;
+
+        switch(rand()%4) {
+        default: break;
+        case 0: {
+            demorect(box, "Layout( UI_LEFT )", hue, 0, UI_LEFT, T, height, M, M, M, M);
+        } break;
+        case 1: {
+            demorect(box, "Layout( UI_HCENTER )", hue, 0, UI_HCENTER, T/2, height, M, M, M, M);
+        } break;
+        case 2: {
+            demorect(box, "Layout( UI_HFILL )", hue, 0, UI_HFILL, T, height, M, M, M, M);
+        } break;
+        case 3: {
+            demorect(box, "Layout( UI_RIGHT )", hue, 0, UI_RIGHT, T/2, height, M, M, M, M);
+        } break;
+        }
+    }
+
+}
+
 void build_wrapdemo(int parent) {
     int col = uiItem();
     uiAppend(parent, col);
     uiSetBox(col, UI_COLUMN);
-    uiSetLayout(col, UI_HFILL|UI_TOP);
+    uiSetLayout(col, UI_FILL);
 
     const int M = 5;
     const int S = 100;
@@ -902,16 +931,19 @@ void build_wrapdemo(int parent) {
 
     int box;
     box = demorect(col, "Box( UI_ROW | UI_WRAP | UI_START )\nLayout( UI_HFILL | UI_TOP )", 0.6f, UI_ROW | UI_WRAP | UI_START, UI_HFILL | UI_TOP, 0, 0, M, M, M, M);
-    fill_wrap_box(box);
+    fill_wrap_row_box(box);
 
     box = demorect(col, "Box( UI_ROW | UI_WRAP | UI_MIDDLE )\nLayout( UI_HFILL | UI_TOP )", 0.6f, UI_ROW | UI_WRAP, UI_HFILL | UI_TOP, 0, 0, M, M, M, M);
-    fill_wrap_box(box);
+    fill_wrap_row_box(box);
 
     box = demorect(col, "Box( UI_ROW | UI_WRAP | UI_END )\nLayout( UI_HFILL | UI_TOP )", 0.6f, UI_ROW | UI_WRAP | UI_END, UI_HFILL | UI_TOP, 0, 0, M, M, M, M);
-    fill_wrap_box(box);
+    fill_wrap_row_box(box);
 
     box = demorect(col, "Box( UI_ROW | UI_WRAP | UI_JUSTIFY )\nLayout( UI_HFILL | UI_TOP )", 0.6f, UI_ROW | UI_WRAP | UI_JUSTIFY, UI_HFILL | UI_TOP, 0, 0, M, M, M, M);
-    fill_wrap_box(box);
+    fill_wrap_row_box(box);
+
+    box = demorect(col, "Box( UI_COLUMN | UI_WRAP | UI_START )\nLayout( UI_LEFT | UI_VFILL )", 0.6f, UI_COLUMN | UI_WRAP | UI_START, UI_LEFT | UI_VFILL, 0, 0, M, M, M, M);
+    fill_wrap_column_box(box);
 }
 
 
diff --git a/oui.h b/oui.h
index 57fa446..f8c011c 100644
--- a/oui.h
+++ b/oui.h
@@ -648,7 +648,9 @@ OUI_EXPORT short uiGetMarginDown(int item);
 // extra item flags
 enum {
     // bit 0-2
-    UI_ITEM_BOX_MASK    = 0x00001F,
+    UI_ITEM_BOX_MODEL_MASK = 0x000007,
+    // bit 0-4
+    UI_ITEM_BOX_MASK       = 0x00001F,
     // bit 5-8
     UI_ITEM_LAYOUT_MASK = 0x0001E0,
     // bit 9-18
@@ -1123,25 +1125,35 @@ static void uiComputeSize(int item, int dim) {
         kid = uiNextSibling(kid);
     }
 
-    if (pitem->size[dim]) {
+    if (pitem->size[dim])
         return;
-    } else if(pitem->flags & UI_FLEX) {
-        if (pitem->flags & UI_WRAP) {
-            // flex model
-            if ((pitem->flags & 1) == (unsigned int)dim) // direction
-                uiComputeStackedSize(pitem, dim);
-            else
-                uiComputeWrappedSize(pitem, dim);
-        } else {
-            // flex model
-            if ((pitem->flags & 1) == (unsigned int)dim) // direction
-                uiComputeStackedSize(pitem, dim);
-            else
-                uiComputeImposedSize(pitem, dim);
-        }
-    } else {
+    switch(pitem->flags & UI_ITEM_BOX_MODEL_MASK) {
+    case UI_COLUMN|UI_WRAP: {
+        // flex model
+        if (dim) // direction
+            uiComputeStackedSize(pitem, 1);
+        else
+            uiComputeImposedSize(pitem, 0);
+    } break;
+    case UI_ROW|UI_WRAP: {
+        // flex model
+        if (!dim) // direction
+            uiComputeStackedSize(pitem, 0);
+        else
+            uiComputeWrappedSize(pitem, 1);
+    } break;
+    case UI_COLUMN:
+    case UI_ROW: {
+        // flex model
+        if ((pitem->flags & 1) == (unsigned int)dim) // direction
+            uiComputeStackedSize(pitem, dim);
+        else
+            uiComputeImposedSize(pitem, dim);
+    } break;
+    default: {
         // layout model
         uiComputeImposedSize(pitem, dim);
+    } break;
     }
 }
 
@@ -1171,7 +1183,7 @@ UI_INLINE void uiArrangeStacked(UIitem *pitem, int dim, bool wrap) {
             } else {
                 extend += pkid->margins[dim] + pkid->size[dim] + pkid->margins[wdim];
             }
-            if (wrap && (extend > space) && (total>1)) {
+            if (wrap && (extend > space) && total) {
                 end_kid = kid;
                 // add marker for subsequent queries
                 pkid->flags |= UI_ITEM_NEWLINE;
@@ -1253,7 +1265,7 @@ UI_INLINE void uiArrangeImposedRange(UIitem *pitem, int dim,
         switch(flags & UI_HFILL) {
         default: break;
         case UI_HCENTER: {
-            pkid->margins[dim] += (space-pkid->size[dim])/2;
+            pkid->margins[dim] += (space-pkid->size[dim])/2 - pkid->margins[wdim];
         } break;
         case UI_RIGHT: {
             pkid->margins[dim] = space-pkid->size[dim]-pkid->margins[wdim];
@@ -1273,7 +1285,7 @@ UI_INLINE void uiArrangeImposed(UIitem *pitem, int dim) {
 }
 
 // superimpose all items according to their alignment
-UI_INLINE void uiArrangeWrappedImposed(UIitem *pitem, int dim) {
+UI_INLINE short uiArrangeWrappedImposed(UIitem *pitem, int dim) {
     int wdim = dim+2;
 
     short offset = pitem->margins[dim];
@@ -1299,28 +1311,43 @@ UI_INLINE void uiArrangeWrappedImposed(UIitem *pitem, int dim) {
     }
 
     uiArrangeImposedRange(pitem, dim, start_kid, -1, offset, need_size);
+    offset += need_size;
+    return offset;
 }
 
 static void uiArrange(int item, int dim) {
     UIitem *pitem = uiItemPtr(item);
 
-    if(pitem->flags & UI_FLEX) {
-        if (pitem->flags & UI_WRAP) {
-            if ((pitem->flags & 1) == (unsigned int)dim) { // direction
-                uiArrangeStacked(pitem, dim, true);
-            } else {
-                uiArrangeWrappedImposed(pitem, dim);
-            }
+    switch(pitem->flags & UI_ITEM_BOX_MODEL_MASK) {
+    case UI_COLUMN|UI_WRAP: {
+        // flex model, wrapping
+        if (dim) { // direction
+            uiArrangeStacked(pitem, 1, true);
+            // this retroactive resize will not effect parent widths
+            short offset = uiArrangeWrappedImposed(pitem, 0);
+            pitem->size[0] = offset - pitem->margins[0];
+        }
+    } break;
+    case UI_ROW|UI_WRAP: {
+        // flex model, wrapping
+        if (!dim) { // direction
+            uiArrangeStacked(pitem, 0, true);
         } else {
-            // flex model
-            if ((pitem->flags & 1) == (unsigned int)dim) // direction
-                uiArrangeStacked(pitem, dim, false);
-            else
-                uiArrangeImposed(pitem, dim);
+            uiArrangeWrappedImposed(pitem, 1);
         }
-    } else {
+    } break;
+    case UI_COLUMN:
+    case UI_ROW: {
+        // flex model
+        if ((pitem->flags & 1) == (unsigned int)dim) // direction
+            uiArrangeStacked(pitem, dim, false);
+        else
+            uiArrangeImposed(pitem, dim);
+    } break;
+    default: {
         // layout model
         uiArrangeImposed(pitem, dim);
+    } break;
     }
 
     int kid = uiFirstChild(item);
@@ -1330,19 +1357,21 @@ static void uiArrange(int item, int dim) {
     }
 }
 
-static void uiNestedLayout(int item, int dim) {
-    uiComputeSize(item,dim);
-    uiArrange(item,dim);
+// vertical layout:
+// compute horizontal: superimposed width of all child items (assume single row)
+// arrange horizontal: arrange all items imposed in-place
+// compute vertical: set size to 0
+// arrange vertical: stack and wrap, vertically and horizontally
 
-    uiComputeSize(item,1-dim);
-    uiArrange(item,1-dim);
-}
 
 void uiLayout() {
     assert(ui_context);
     if (!ui_context->count) return;
 
-    uiNestedLayout(0,0);
+    uiComputeSize(0,0);
+    uiArrange(0,0);
+    uiComputeSize(0,1);
+    uiArrange(0,1);
 
     uiValidateStateItems();
     // drawing routines may require this to be set already