Add new GridFlow layout.

This mimics the 'spreadsheet' behavior. Columns and/or rows can have
equal sizes, or adapt to their content - but always in a grid way (i.e.
all items in a same column will always have same available width, and
all items in a same row will always have same available height).
Also, you can fill (order) the grid in a row- or column-major way.

Not used anywhere for now.

Differential: https://developer.blender.org/D2395

3 files changed, 423 insertions, 3 deletions

diff --git a/source/blender/editors/include/UI_interface.h b/source/blender/editors/include/UI_interface.h
index a283068853c..dee3104e6f4 100644
--- a/source/blender/editors/include/UI_interface.h
+++ b/source/blender/editors/include/UI_interface.h
@@ -979,6 +979,8 @@ bool uiLayoutGetPropSep(uiLayout *layout);
 uiLayout *uiLayoutRow(uiLayout *layout, int align);
 uiLayout *uiLayoutColumn(uiLayout *layout, int align);
 uiLayout *uiLayoutColumnFlow(uiLayout *layout, int number, int align);
+uiLayout *uiLayoutGridFlow(
+        uiLayout *layout, int row_major, int num_columns, int even_columns, int even_rows, int align);
 uiLayout *uiLayoutBox(uiLayout *layout);
 uiLayout *uiLayoutListBox(uiLayout *layout, struct uiList *ui_list, struct PointerRNA *ptr, struct PropertyRNA *prop,
                           struct PointerRNA *actptr, struct PropertyRNA *actprop);
diff --git a/source/blender/editors/interface/interface_layout.c b/source/blender/editors/interface/interface_layout.c
index b4677d95361..339b333a5fb 100644
--- a/source/blender/editors/interface/interface_layout.c
+++ b/source/blender/editors/interface/interface_layout.c
@@ -37,6 +37,7 @@
 #include "DNA_armature_types.h"
 #include "DNA_userdef_types.h"
 
+#include "BLI_alloca.h"
 #include "BLI_listbase.h"
 #include "BLI_string.h"
 #include "BLI_rect.h"
@@ -101,6 +102,7 @@ typedef enum uiItemType {
 	ITEM_LAYOUT_COLUMN,
 	ITEM_LAYOUT_COLUMN_FLOW,
 	ITEM_LAYOUT_ROW_FLOW,
+	ITEM_LAYOUT_GRID_FLOW,
 	ITEM_LAYOUT_BOX,
 	ITEM_LAYOUT_ABSOLUTE,
 	ITEM_LAYOUT_SPLIT,
@@ -152,6 +154,7 @@ struct uiLayout {
 	bool enabled;
 	bool redalert;
 	bool keepaspect;
+	bool variable_size;  /* For layouts inside gridflow, they and their items shall never have a fixed maximal size. */
 	char alignment;
 	char emboss;
 };
@@ -162,6 +165,22 @@ typedef struct uiLayoutItemFlow {
 	int totcol;
 } uiLayoutItemFlow;
 
+typedef struct uiLayoutItemGridFlow {
+	uiLayout litem;
+
+	/* Extra parameters */
+	bool row_major;     /* Fill first row first, instead of filling first column first. */
+	bool even_columns;  /* Same width for all columns. */
+	bool even_rows;     /* Same height for all rows. */
+	/* If positive, absolute fixed number of columns.
+	 * If 0, fully automatic (based on available width).
+	 * If negative, automatic but only generates number of columns/rows multiple of given (absolute) value. */
+	int num_columns;
+
+	/* Pure internal runtime storage. */
+	int tot_items, tot_columns, tot_rows;
+} uiLayoutItemGridFlow;
+
 typedef struct uiLayoutItemBx {
 	uiLayout litem;
 	uiBut *roundbox;
@@ -237,6 +256,13 @@ static int ui_layout_vary_direction(uiLayout *layout)
 	        UI_ITEM_VARY_X : UI_ITEM_VARY_Y);
 }
 
+static bool ui_layout_variable_size(uiLayout *layout)
+{
+	/* Note that this code is probably a bit flacky, we'd probably want to know whether it's variable in X and/or Y,
+	 * etc. But for now it mimics previous one, with addition of variable flag set for children of gridflow layouts. */
+	return ui_layout_vary_direction(layout) == UI_ITEM_VARY_X || layout->variable_size;
+}
+
 /* estimated size of text + icon */
 static int ui_text_icon_width(uiLayout *layout, const char *name, int icon, bool compact)
 {
@@ -246,7 +272,7 @@ static int ui_text_icon_width(uiLayout *layout, const char *name, int icon, bool
 	if (icon && !name[0])
 		return unit_x;  /* icon only */
 
-	variable = (ui_layout_vary_direction(layout) == UI_ITEM_VARY_X);
+	variable = ui_layout_variable_size(layout);
 
 	if (variable) {
 		if (layout->alignment != UI_LAYOUT_ALIGN_EXPAND) {
@@ -347,6 +373,7 @@ static int ui_layout_local_dir(uiLayout *layout)
 			return UI_LAYOUT_HORIZONTAL;
 		case ITEM_LAYOUT_COLUMN:
 		case ITEM_LAYOUT_COLUMN_FLOW:
+		case ITEM_LAYOUT_GRID_FLOW:
 		case ITEM_LAYOUT_SPLIT:
 		case ITEM_LAYOUT_ABSOLUTE:
 		case ITEM_LAYOUT_BOX:
@@ -713,7 +740,7 @@ static uiBut *ui_item_with_label(
 			w_label = (int)((w_hint * 2) * UI_ITEM_PROP_SEP_DIVIDE);
 		}
 		else {
-			if (ui_layout_vary_direction(layout) == UI_ITEM_VARY_X) {
+			if (ui_layout_variable_size(layout)) {
 				/* w_hint is width for label in this case. Use a default width for property button(s) */
 				prop_but_width = UI_UNIT_X * 5;
 				w_label = w_hint;
@@ -1426,7 +1453,7 @@ static void ui_item_rna_size(
 		else
 			h += len * UI_UNIT_Y;
 	}
-	else if (ui_layout_vary_direction(layout) == UI_ITEM_VARY_X) {
+	else if (ui_layout_variable_size(layout)) {
 		if (type == PROP_BOOLEAN && name[0])
 			w += UI_UNIT_X / 5;
 		else if (type == PROP_ENUM && !icon_only)
@@ -2834,6 +2861,355 @@ static void ui_litem_layout_column_flow(uiLayout *litem)
 	litem->y = miny;
 }
 
+/* multi-column and multi-row layout. */
+typedef struct UILayoutGridFlowInput {
+	/* General layout controll settings. */
+	const bool row_major : 1;  /* Fill rows before columns */
+	const bool even_columns : 1;  /* All columns will have same width. */
+	const bool even_rows : 1;  /* All rows will have same height. */
+	const int space_x;  /* Space between columns. */
+	const int space_y;  /* Space between rows. */
+	/* Real data about current position and size of this layout item (either estimated, or final values). */
+	const int litem_w;  /* Layout item width. */
+	const int litem_x;  /* Layout item X position. */
+	const int litem_y;  /* Layout item Y position. */
+	/* Actual number of columns and rows to generate (computed from first pass usually). */
+	const int tot_columns;  /* Number of columns. */
+	const int tot_rows;  /* Number of rows. */
+} UILayoutGridFlowInput;
+
+typedef struct UILayoutGridFlowOutput {
+	int *tot_items;  /* Total number of items in this grid layout. */
+	/* Width / X pos data. */
+	float *global_avg_w;  /* Computed average width of the columns. */
+	int *cos_x_array;  /* Computed X coordinate of each column. */
+	int *widths_array;  /* Computed width of each column. */
+	int *tot_w;  /* Computed total width. */
+	/* Height / Y pos data. */
+	int *global_max_h;  /* Computed height of the tallest item in the grid. */
+	int *cos_y_array;  /* Computed Y coordinate of each column. */
+	int *heights_array;  /* Computed height of each column. */
+	int *tot_h;  /* Computed total height. */
+} UILayoutGridFlowOutput;
+
+static void ui_litem_grid_flow_compute(
+        ListBase *items, UILayoutGridFlowInput *parameters, UILayoutGridFlowOutput *results)
+{
+	uiItem *item;
+	int i;
+
+	float tot_w = 0.0f, tot_h = 0.0f;
+	float global_avg_w = 0.0f, global_totweight_w = 0.0f;
+	int global_max_h = 0;
+
+	float *avg_w = NULL, *totweight_w = NULL;
+	int *max_h = NULL;
+
+	BLI_assert(parameters->tot_columns != 0 || (results->cos_x_array == NULL && results->widths_array == NULL && results->tot_w == NULL));
+	BLI_assert(parameters->tot_rows != 0 || (results->cos_y_array == NULL && results->heights_array == NULL && results->tot_h == NULL));
+
+	if (results->tot_items) {
+		*results->tot_items = 0;
+	}
+
+	if (items->first == NULL) {
+		if (results->global_avg_w) {
+			*results->global_avg_w = 0.0f;
+		}
+		if (results->global_max_h) {
+			*results->global_max_h = 0;
+		}
+		return;
+	}
+
+	if (parameters->tot_columns != 0) {
+		avg_w = BLI_array_alloca(avg_w, parameters->tot_columns);
+		totweight_w = BLI_array_alloca(totweight_w, parameters->tot_columns);
+		memset(avg_w, 0, sizeof(*avg_w) * parameters->tot_columns);
+		memset(totweight_w, 0, sizeof(*totweight_w) * parameters->tot_columns);
+	}
+	if (parameters->tot_rows != 0) {
+		max_h = BLI_array_alloca(max_h, parameters->tot_rows);
+		memset(max_h, 0, sizeof(*max_h) * parameters->tot_rows);
+	}
+
+	for (i = 0, item = items->first; item; item = item->next, i++) {
+		int item_w, item_h;
+		ui_item_size(item, &item_w, &item_h);
+
+		global_avg_w += (float)(item_w * item_w);
+		global_totweight_w += (float)item_w;
+		global_max_h = max_ii(global_max_h, item_h);
+
+		if (parameters->tot_rows != 0 && parameters->tot_columns != 0) {
+			const int index_col = parameters->row_major ? i % parameters->tot_columns : i / parameters->tot_rows;
+			const int index_row = parameters->row_major ? i / parameters->tot_columns : i % parameters->tot_rows;
+
+			avg_w[index_col] += (float)(item_w * item_w);
+			totweight_w[index_col] += (float)item_w;
+
+			max_h[index_row] = max_ii(max_h[index_row], item_h);
+		}
+
+		if (results->tot_items) {
+			(*results->tot_items)++;
+		}
+	}
+
+	/* Finalize computing of column average sizes */
+	global_avg_w /= global_totweight_w;
+	if (parameters->tot_columns != 0) {
+		for (i = 0; i < parameters->tot_columns; i++) {
+			avg_w[i] /= totweight_w[i];
+			tot_w += avg_w[i];
+		}
+		if (parameters->even_columns) {
+			tot_w = ceilf(global_avg_w) * parameters->tot_columns;
+		}
+	}
+	/* Finalize computing of rows max sizes */
+	if (parameters->tot_rows != 0) {
+		for (i = 0; i < parameters->tot_rows; i++) {
+			tot_h += max_h[i];
+		}
+		if (parameters->even_rows) {
+			tot_h = global_max_h * parameters->tot_columns;
+		}
+	}
+
+	/* Compute positions and sizes of all cells. */
+	if (results->cos_x_array != NULL && results->widths_array != NULL) {
+		/* We enlarge/narrow columns evenly to match available width. */
+		const float wfac = (float)(parameters->litem_w - (parameters->tot_columns - 1) * parameters->space_x) / tot_w;
+
+		for (int col = 0; col < parameters->tot_columns; col++) {
+			results->cos_x_array[col] = col ? results->cos_x_array[col - 1] + results->widths_array[col - 1] + parameters->space_x : parameters->litem_x;
+			if (parameters->even_columns) {
+				/*                     (<                        remaining width                          > - <       space between remaining columns              >) / <     remaining columns    > */
+				results->widths_array[col] = ((parameters->litem_w - (results->cos_x_array[col] - parameters->litem_x)) - (parameters->tot_columns - col - 1) * parameters->space_x) / (parameters->tot_columns - col);
+			}
+			else if (col == parameters->tot_columns - 1) {
+				/* Last column copes width rounding errors... */
+				results->widths_array[col] = parameters->litem_w - (results->cos_x_array[col] - parameters->litem_x);
+			}
+			else {
+				results->widths_array[col] = (int)(avg_w[col] * wfac);
+			}
+		}
+	}
+	if (results->cos_y_array != NULL && results->heights_array != NULL) {
+		for (int row = 0; row < parameters->tot_rows; row++) {
+			if (parameters->even_rows) {
+				results->heights_array[row] = global_max_h;
+			}
+			else {
+				results->heights_array[row] = max_h[row];
+			}
+			results->cos_y_array[row] = row ? results->cos_y_array[row - 1] - parameters->space_y - results->heights_array[row] : parameters->litem_y - results->heights_array[row];
+		}
+	}
+
+	if (results->global_avg_w) {
+		*results->global_avg_w = global_avg_w;
+	}
+	if (results->global_max_h) {
+		*results->global_max_h = global_max_h;
+	}
+	if (results->tot_w) {
+		*results->tot_w = (int)tot_w + parameters->space_x * (parameters->tot_columns - 1);
+	}
+	if (results->tot_h) {
+		*results->tot_h = tot_h + parameters->space_y * (parameters->tot_rows - 1);
+	}
+}
+
+static void ui_litem_estimate_grid_flow(uiLayout *litem)
+{
+	uiStyle *style = litem->root->style;
+	uiLayoutItemGridFlow *gflow = (uiLayoutItemGridFlow *)litem;
+
+	const int space_x = style->columnspace;
+	const int space_y = style->buttonspacey;
+
+	/* Estimate average needed width and height per item. */
+	{
+		float avg_w;
+		int max_h;
+
+		ui_litem_grid_flow_compute(
+		            &litem->items,
+		            &((UILayoutGridFlowInput) {
+		                  .row_major = gflow->row_major,
+		                  .even_columns = gflow->even_columns,
+		                  .even_rows = gflow->even_rows,
+		                  .litem_w = litem->w,
+		                  .litem_x = litem->x,
+		                  .litem_y = litem->y,
+		                  .space_x = space_x,
+		                  .space_y = space_y,
+		              }),
+		            &((UILayoutGridFlowOutput) {
+		                  .tot_items = &gflow->tot_items,
+		                  .global_avg_w = &avg_w,
+		                  .global_max_h = &max_h,
+		              }));
+
+		if (gflow->tot_items == 0) {
+			litem->w = litem->h = 0;
+			gflow->tot_columns = gflow->tot_rows = 0;
+			return;
+		}
+
+		/* Even in varying column width case, we fix our columns number from weighted average width of items,
+		 * a proper solving of required width would be too costly, and this should give reasonably good results
+		 * in all resonable cases... */
+		if (gflow->num_columns > 0) {
+			gflow->tot_columns = gflow->num_columns;
+		}
+		else {
+			if (avg_w == 0.0f) {
+				gflow->tot_columns = 1;
+			}
+			else {
+				gflow->tot_columns = min_ii(max_ii((int)(litem->w / avg_w), 1), gflow->tot_items);
+			}
+		}
+		gflow->tot_rows = (int)ceilf((float)gflow->tot_items / gflow->tot_columns);
+
+		/* Try to tweak number of columns and rows to get better filling of last column or row,
+		 * and apply 'modulo' value to number of columns or rows.
+		 * Note that modulo does not prevent ending with fewer columns/rows than modulo, if mandatory
+		 * to avoid empty column/row. */
+		{
+			const int modulo = (gflow->num_columns < -1) ? -gflow->num_columns : 0;
+			const int step = modulo ? modulo : 1;
+
+			if (gflow->row_major) {
+				/* Adjust number of columns to be mutiple of given modulo. */
+				if (modulo && gflow->tot_columns % modulo != 0 && gflow->tot_columns > modulo) {
+					gflow->tot_columns = gflow->tot_columns - (gflow->tot_columns % modulo);
+				}
+				/* Find smallest number of columns conserving computed optimal number of rows. */
+				for (gflow->tot_rows = (int)ceilf((float)gflow->tot_items / gflow->tot_columns);
+				     (gflow->tot_columns - step) > 0 &&
+				     (int)ceilf((float)gflow->tot_items / (gflow->tot_columns - step)) <= gflow->tot_rows;
+				     gflow->tot_columns -= step);
+			}
+			else {
+				/* Adjust number of rows to be mutiple of given modulo. */
+				if (modulo && gflow->tot_rows % modulo != 0) {
+					gflow->tot_rows = min_ii(gflow->tot_rows + modulo - (gflow->tot_rows % modulo), gflow->tot_items);
+				}
+				/* Find smallest number of rows conserving computed optimal number of columns. */
+				for (gflow->tot_columns = (int)ceilf((float)gflow->tot_items / gflow->tot_rows);
+				     (gflow->tot_rows - step) > 0 &&
+				     (int)ceilf((float)gflow->tot_items / (gflow->tot_rows - step)) <= gflow->tot_columns;
+				     gflow->tot_rows -= step);
+			}
+		}
+
+		/* Set evenly-spaced axes size (quick optimization in case we have even columns and rows). */
+		if (gflow->even_columns && gflow->even_rows) {
+			litem->w = (int)(gflow->tot_columns * avg_w) + space_x * (gflow->tot_columns - 1);
+			litem->h = (int)(gflow->tot_rows * max_h) + space_y * (gflow->tot_rows - 1);
+			return;
+		}
+	}
+
+	/* Now that we have our final number of columns and rows,
+	 * we can compute actual needed space for non-evenly sized axes. */
+	{
+		int tot_w, tot_h;
+
+		ui_litem_grid_flow_compute(
+		            &litem->items,
+		            &((UILayoutGridFlowInput) {
+		                  .row_major = gflow->row_major,
+		                  .even_columns = gflow->even_columns,
+		                  .even_rows = gflow->even_rows,
+		                  .litem_w = litem->w,
+		                  .litem_x = litem->x,
+		                  .litem_y = litem->y,
+		                  .space_x = space_x,
+		                  .space_y = space_y,
+		                  .tot_columns = gflow->tot_columns,
+		                  .tot_rows = gflow->tot_rows,
+		              }),
+		            &((UILayoutGridFlowOutput) {
+		                  .tot_w = &tot_w,
+		                  .tot_h = &tot_h,
+		              }));
+
+		litem->w = tot_w;
+		litem->h = tot_h;
+	}
+}
+
+static void ui_litem_layout_grid_flow(uiLayout *litem)
+{
+	int i;
+	uiStyle *style = litem->root->style;
+	uiLayoutItemGridFlow *gflow = (uiLayoutItemGridFlow *)litem;
+	uiItem *item;
+
+	if (gflow->tot_items == 0) {
+		litem->w = litem->h = 0;
+		return;
+	}
+
+	BLI_assert(gflow->tot_columns > 0);
+	BLI_assert(gflow->tot_rows > 0);
+
+	const int space_x = style->columnspace;
+	const int space_y = style->buttonspacey;
+
+	int *widths = BLI_array_alloca(widths, gflow->tot_columns);
+	int *heights = BLI_array_alloca(heights, gflow->tot_rows);
+	int *cos_x = BLI_array_alloca(cos_x, gflow->tot_columns);
+	int *cos_y = BLI_array_alloca(cos_y, gflow->tot_rows);
+
+	/* This time we directly compute coordinates and sizes of all cells. */
+	ui_litem_grid_flow_compute(
+	            &litem->items,
+	            &((UILayoutGridFlowInput) {
+	                  .row_major = gflow->row_major,
+	                  .even_columns = gflow->even_columns,
+	                  .even_rows = gflow->even_rows,
+	                  .litem_w = litem->w,
+	                  .litem_x = litem->x,
+	                  .litem_y = litem->y,
+	                  .space_x = space_x,
+	                  .space_y = space_y,
+	                  .tot_columns = gflow->tot_columns,
+	                  .tot_rows = gflow->tot_rows,
+	              }),
+	            &((UILayoutGridFlowOutput) {
+	                  .cos_x_array = cos_x,
+	                  .cos_y_array = cos_y,
+	                  .widths_array = widths,
+	                  .heights_array = heights,
+	              }));
+
+	for (item = litem->items.first, i = 0; item; item = item->next, i++) {
+		const int col = gflow->row_major ? i % gflow->tot_columns : i / gflow->tot_rows;
+		const int row = gflow->row_major ? i / gflow->tot_columns : i % gflow->tot_rows;
+		int item_w, item_h;
+		ui_item_size(item, &item_w, &item_h);
+
+		const int w = widths[col];
+		const int h = heights[row];
+
+		item_w = (litem->alignment == UI_LAYOUT_ALIGN_EXPAND) ? w : min_ii(w, item_w);
+		item_h = (litem->alignment == UI_LAYOUT_ALIGN_EXPAND) ? h : min_ii(h, item_h);
+
+		ui_item_position(item, cos_x[col], cos_y[row], item_w, item_h);
+	}
+
+	litem->h = litem->y - cos_y[gflow->tot_rows - 1];
+	litem->x = (cos_x[gflow->tot_columns - 1] - litem->x) + widths[gflow->tot_columns - 1];
+	litem->y = litem->y - litem->h;
+}
+
 /* free layout */
 static void ui_litem_estimate_absolute(uiLayout *litem)
 {
@@ -3007,6 +3383,8 @@ static void ui_litem_init_from_parent(uiLayout *litem, uiLayout *layout, int ali
 {
 	litem->root = layout->root;
 	litem->align = align;
+	/* Children of gridflow layout shall never have "ideal big size" returned as estimated size. */
+	litem->variable_size = layout->variable_size || layout->item.type == ITEM_LAYOUT_GRID_FLOW;
 	litem->active = true;
 	litem->enabled = true;
 	litem->context = layout->context;
@@ -3064,6 +3442,26 @@ uiLayout *uiLayoutColumnFlow(uiLayout *layout, int number, int align)
 	return &flow->litem;
 }
 
+uiLayout *uiLayoutGridFlow(
+        uiLayout *layout, int row_major, int num_columns, int even_columns, int even_rows, int align)
+{
+	uiLayoutItemGridFlow *flow;
+
+	flow = MEM_callocN(sizeof(uiLayoutItemGridFlow), __func__);
+	flow->litem.item.type = ITEM_LAYOUT_GRID_FLOW;
+	ui_litem_init_from_parent(&flow->litem, layout, align);
+
+	flow->litem.space = (flow->litem.align) ? 0 : layout->root->style->columnspace;
+	flow->row_major = row_major;
+	flow->num_columns = num_columns;
+	flow->even_columns = even_columns;
+	flow->even_rows = even_rows;
+
+	UI_block_layout_set_current(layout->root->block, &flow->litem);
+
+	return &flow->litem;
+}
+
 static uiLayoutItemBx *ui_layout_box(uiLayout *layout, int type)
 {
 	uiLayoutItemBx *box;
@@ -3359,6 +3757,9 @@ static void ui_item_estimate(uiItem *item)
 			case ITEM_LAYOUT_COLUMN_FLOW:
 				ui_litem_estimate_column_flow(litem);
 				break;
+			case ITEM_LAYOUT_GRID_FLOW:
+				ui_litem_estimate_grid_flow(litem);
+				break;
 			case ITEM_LAYOUT_ROW:
 				ui_litem_estimate_row(litem);
 				break;
@@ -3458,6 +3859,9 @@ static void ui_item_layout(uiItem *item)
 			case ITEM_LAYOUT_COLUMN_FLOW:
 				ui_litem_layout_column_flow(litem);
 				break;
+			case ITEM_LAYOUT_GRID_FLOW:
+				ui_litem_layout_grid_flow(litem);
+				break;
 			case ITEM_LAYOUT_ROW:
 				ui_litem_layout_row(litem);
 				break;
@@ -3737,6 +4141,7 @@ static void ui_intro_items(DynStr *ds, ListBase *lb)
 			case ITEM_LAYOUT_COLUMN:      BLI_dynstr_append(ds, "'type':'COLUMN', "); break;
 			case ITEM_LAYOUT_COLUMN_FLOW: BLI_dynstr_append(ds, "'type':'COLUMN_FLOW', "); break;
 			case ITEM_LAYOUT_ROW_FLOW:    BLI_dynstr_append(ds, "'type':'ROW_FLOW', "); break;
+			case ITEM_LAYOUT_GRID_FLOW:   BLI_dynstr_append(ds, "'type':'GRID_FLOW', "); break;
 			case ITEM_LAYOUT_BOX:         BLI_dynstr_append(ds, "'type':'BOX', "); break;
 			case ITEM_LAYOUT_ABSOLUTE:    BLI_dynstr_append(ds, "'type':'ABSOLUTE', "); break;
 			case ITEM_LAYOUT_SPLIT:       BLI_dynstr_append(ds, "'type':'SPLIT', "); break;
diff --git a/source/blender/makesrna/intern/rna_ui_api.c b/source/blender/makesrna/intern/rna_ui_api.c
index 3a7a2edd660..ab4bdc8164b 100644
--- a/source/blender/makesrna/intern/rna_ui_api.c
+++ b/source/blender/makesrna/intern/rna_ui_api.c
@@ -518,6 +518,19 @@ void RNA_api_ui_layout(StructRNA *srna)
 	RNA_def_function_return(func, parm);
 	RNA_def_boolean(func, "align", false, "", "Align buttons to each other");
 
+	func = RNA_def_function(srna, "grid_flow", "uiLayoutGridFlow");
+	RNA_def_boolean(func, "row_major", false, "", "Fill row by row, instead of column by column");
+	RNA_def_int(func, "num_columns", 0, INT_MIN, INT_MAX, "",
+	            "Number of columns, positive are absolute fixed numbers, 0 is automatic, negative are "
+	            "automatic multiple numbers along major axis (e.g. -2 will only produce 2, 4, 6 etc. "
+	            "columns for row major layout, and 2, 4, 6 etc. rows for column major layout)",
+	            INT_MIN, INT_MAX);
+	RNA_def_boolean(func, "even_columns", false, "", "All columns will have the same width");
+	RNA_def_boolean(func, "even_rows", false, "", "All rows will have the same height");
+	RNA_def_boolean(func, "align", false, "", "Align buttons to each other");
+	parm = RNA_def_pointer(func, "layout", "UILayout", "", "Sub-layout to put items in");
+	RNA_def_function_return(func, parm);
+
 	/* box layout */
 	func = RNA_def_function(srna, "box", "uiLayoutBox");
 	parm = RNA_def_pointer(func, "layout", "UILayout", "", "Sub-layout to put items in");