The Grid layout is a subset of [CSS Flexbox](https://css-tricks.com/snippets/css/complete-guide-grid/).
It can arrange items into 2D "table" that has rows or columns (tracks). The item can span through multiple columns or rows.
The track's size can be set in pixel, to the largest item (`LV_GRID_CONTENT`) or in "Free unit" (FR) to distribute the free space proportionally.
To make an object grid container call `lv_obj_set_layout(obj, LV_LAYOUT_GRID)`.
Note that, the grid layout needs to enabled with `LV_USE_GRID` in `lv_conf.h`.
## Terms
- tracks: the rows or columns
- free unit (FR): if set on track's size is set in `FR` it will grow to fill the remaining space on the parent.
- gap: the space between the rows and columns or the items on a track
## Simple interface
With the following functions you can simple set a Grid layout on any parent.
### Grid descriptors
First you need to describe the size of rows and columns. It can be done by declaring 2 arrays and the the track sizes in them. The last element must be `LV_GRID_TEMPLATE_LAST`.
For example:
```
static lv_coord_t column_dsc[] = {100, 400, LV_GRID_TEMPLATE_LAST}; /*2 columns with 100 and 400 ps width*/
To set the descriptors on a parent use `lv_obj_set_grid_dsc_array(obj, col_dsc, row_dsc)`.
Besides simple settings the size in pixel you can use two special values:
-`LV_GRID_CONTENT` set the width to the largest children on this track
-`LV_GRID_FR(X)` tell what portion of the remaining space should be used by this track. Larger value means larger space.
### Grid items
By default the children are not added to the grid but they needs to be added manually to a cell.
To to this call `lv_obj_set_grid_cell(child, column_align, column_pos, column_span, row_align, row_pos, row_span)`.
`column_align` and `row_align` tells how to align the children in its cell. The possible values are:
-`LV_GRID_ALIGN_START` means left on a horizontally and top vertically. (default)
-`LV_GRID_ALIGN_END` means right on a horizontally and bottom vertically
-`LV_GRID_ALIGN_CENTER` simply center
`colum_pos` and `row_pos` means the zero based index of the cell into the item should be placed.
`colum_span` and `row_span` means how many tracks should the item involve from the start cell. Must be > 1.
### Grid align
If there are some empty space the track can be aligned several ways:
-`LV_GRID_ALIGN_START` means left on a horizontally and top vertically. (default)
-`LV_GRID_ALIGN_END` means right on a horizontally and bottom vertically
-`LV_GRID_ALIGN_CENTER` simply center
-`LV_GRID_ALIGN_SPACE_EVENLY` items are distributed so that the spacing between any two items (and the space to the edges) is equal. Not applies to `track_cross_place`.
-`LV_GRID_ALIGN_SPACE_AROUND` items are evenly distributed in the track with equal space around them.
Note that visually the spaces aren’t equal, since all the items have equal space on both sides.
The first item will have one unit of space against the container edge, but two units of space between the next item because that next item has its own spacing that applies. Not applies to `track_cross_place`.
-`LV_GRID_ALIGN_SPACE_BETWEEN` items are evenly distributed in the track: first item is on the start line, last item on the end line. Not applies to `track_cross_place`.
To set the track's alignment use `lv_obj_set_grid_align(obj, column_align, row_align)`.
## Style interface
All the Grid related values are style properties under the hood and you can use them similarly to any other style properties. The following Grid related style properties exist:
-`GRID_COLUMN_DSC_ARRAY`
-`GRID_ROW_DSC_ARRAY`
-`GRID_COLUMN_ALIGN`
-`GRID_ROW_ALIGN`
-`GRID_CELL_X_ALIGN`
-`GRID_CELL_COLUMN_POS`
-`GRID_CELL_COLUMN_SPAN`
-`GRID_CELL_Y_ALIGN`
-`GRID_CELL_ROW_POS`
-`GRID_CELL_ROW_SPAN`
## Other features
### RTL
If the base direction of the container is set the `LV_BASE_DIR_RTL` the meaning of `LV_GRID_ALIGN_START` and `LV_GRID_ALIGN_END` is swapped. I.e. `START` will mean right.
