# The source code

    /**
     * @class Ext.layout.ColumnLayout
     * @extends Ext.layout.ContainerLayout
     * This is the layout style of choice for creating structural layouts in a multi-column format where the width of
     * each column can be specified as a percentage or fixed width, but the height is allowed to vary based on the content.
     * This class is intended to be extended or created via the layout:'column' {@link Ext.Container#layout} config,
     * and should generally not need to be created directly via the new keyword.
     * ColumnLayout does not have any direct config options (other than inherited ones), but it does support a
     * specific config property of columnWidth that can be included in the config of any panel added to it.  The
     * layout will use the columnWidth (if present) or width of each panel during layout to determine how to size each panel.
     * If width or columnWidth is not specified for a given panel, its width will default to the panel's width (or auto).
     * The width property is always evaluated as pixels, and must be a number greater than or equal to 1.
     * The columnWidth property is always evaluated as a percentage, and must be a decimal value greater than 0 and
     * less than 1 (e.g., .25).
     * The basic rules for specifying column widths are pretty simple.  The logic makes two passes through the
     * set of contained panels.  During the first layout pass, all panels that either have a fixed width or none
     * specified (auto) are skipped, but their widths are subtracted from the overall container width.  During the second
     * pass, all panels with columnWidths are assigned pixel widths in proportion to their percentages based on
     * the total remaining container width.  In other words, percentage width panels are designed to fill the space
     * left over by all the fixed-width and/or auto-width panels.  Because of this, while you can specify any number of columns
     * with different percentages, the columnWidths must always add up to 1 (or 100%) when added together, otherwise your
     * layout may not render as expected.  Example usage:
     *
    // All columns are percentages -- they must add up to 1
    var p = new Ext.Panel({
        title: 'Column Layout - Percentage Only',
        layout:'column',
        items: [{
            title: 'Column 1',
            columnWidth: .25
        },{
            title: 'Column 2',
            columnWidth: .6
        },{
            title: 'Column 3',
            columnWidth: .15
        }]
    });

    // Mix of width and columnWidth -- all columnWidth values must add up
    // to 1. The first column will take up exactly 120px, and the last two
    // columns will fill the remaining container width.
    var p = new Ext.Panel({
        title: 'Column Layout - Mixed',
        layout:'column',
        items: [{
            title: 'Column 1',
            width: 120
        },{
            title: 'Column 2',
            columnWidth: .8
        },{
            title: 'Column 3',
            columnWidth: .2
        }]
    });

     */
    Ext.layout.ColumnLayout = Ext.extend(Ext.layout.ContainerLayout, {
        // private
        monitorResize:true,

        extraCls: 'x-column',

        scrollOffset : 0,

        // private

        targetCls: 'x-column-layout-ct',

        isValidParent : function(c, target){
            return c.getPositionEl().dom.parentNode == this.innerCt.dom;
        },

        // private
        onLayout : function(ct, target){
            var cs = ct.items.items, len = cs.length, c, i;

            if(!this.innerCt){
                // the innerCt prevents wrapping and shuffling while
                // the container is resizing
                this.innerCt = target.createChild({cls:'x-column-inner'});
                this.innerCt.createChild({cls:'x-clear'});
            }
            this.renderAll(ct, this.innerCt);

            var size = target.getViewSize(true);

            if(size.width < 1 && size.height < 1){ // display none?
                return;
            }

            var w = size.width - this.scrollOffset,
                h = size.height,
                pw = w;

            this.innerCt.setWidth(w);

            // some columns can be percentages while others are fixed
            // so we need to make 2 passes

            for(i = 0; i < len; i++){
                c = cs[i];
                if(!c.columnWidth){
                    pw -= (c.getSize().width + c.getPositionEl().getMargins('lr'));
                }
            }

            pw = pw < 0 ? 0 : pw;

            for(i = 0; i < len; i++){
                c = cs[i];
                if(c.columnWidth){
                    c.setSize(Math.floor(c.columnWidth * pw) - c.getPositionEl().getMargins('lr'));
                }
            }
        }

        /**
         * @property activeItem
         * @hide
         */
    });

    Ext.Container.LAYOUTS['column'] = Ext.layout.ColumnLayout;