[Lazarus] Autosize behaviour

[Michael Van Canneyt]

On Wed, 7 Apr 2010, Hans-Peter Diettrich wrote:

> Michael Van Canneyt schrieb:
>
>>> IMO it's quite simple. A layout affects the position of child controls 
>>> inside a container control, nothing else. Borders, Constraints and 
>>> Autosize are general properties of all controls, which must be handled 
>>> in/by the control itself.
>> 
>> I agree for Constraints, but not the other two.
>> 
>> It is in contradiction with what Mattias said, where he claimed that
>> when doing layouting you must always work inside-out and outside-in.
>> Borderspacing IS used when layouting: it determines the available space
>> for childs inside/outside the control.
>
> The control determines its client extent from given bounds, by taking into 
> account its specified border style. A layout manager has no idea of such 
> borders, bevels etc., and also not of the visible rectangle of a 
> TScrollingWindowControl.

From

http://wiki.lazarus.freepascal.org/Autosize_/_Layout#Align_and_BorderSpacing

"The space of BorderSpacing and of the parent's ChildSizing is applied to
aligned controls. The memo below has Align=alClient"

BorderSpacing has nothing to do with border style or bevels. It is an EXTRA
margin. Border style and bevels determine the ClientRect of a control, and
as Mattias said, they must be queried from the control itself.

>
>> Autosize as well: if autosize is true, then the size of the control
>> changes, and therefor the layout internal to the control, but also 
>> externally. Hence it belongs in the layouter.
>
> In the simplest case the layouter has not to care about autosize at all. The 
> control determines its required extent, based on e.g. font size and 
> nationalized text, and reports it as its required extent. There is nothing 
> beyond that extent that a layout manager has to know about.
>
> Only when a control can adopt itself to different *given* extents, by e.g. 
> breaking its content into multiple lines, a layout manager has to split the 
> available extent into zones for the client controls. Such a layout manager 
> would accept an extent in one direction, and calculate the resulting extent 
> in the other direction, or spread the client controls evenly. This is a 
> different behaviour from the beforementioned Autosize of controls with no 
> child controls.

AutoSize for a panel explicitly is about child controls, and therefor
layouting.

Unfortunately Borland used AutoSize for 2 different things:
- Resize control to accomodate child controls (as e.g. in TPanel)
- To accomodate for 'native content', such as in TLabel.

They should have been separate properties. I am talking only about
the first one. The second one, obviously, is only necessary for the 
control itself.

>> IMHO a control needs only 5 properties: top/left/width,height and
>> constraints. All the rest is layouting.
>
> You mean that every control should have borders or bevels, as specified by 
> the layout manager? How should such a manager know about different border 
> styles for its client controls?

It does not need to. ClientRect is used for this.

Michael.