1. Reusable Graphics Objects UC Berkeley Fall 2004, E77 http://jagger. me
Reusable Graphics Objects UC Berkeley Fall 2004, E77 Copyright 2005, Andy Packard. This work is licensed under the Creative Commons Attribution-ShareAlike License. To view a copy of this license, visit or send a letter to Creative Commons, 559 Nathan Abbott Way, Stanford, California 94305, USA.

2. Writing reusable graphical based applications
In order to write a reusable, graphical based application using Matlab HandleGraphics, the “application” should mimic the attributes of the basic Matlab HandleGraphics objects
referred to by a handle
get/set interface by which its properties (“state”) are accessed
store hidden, globally accessible data
have events associated with changes in its state
This is relatively straightforward to do, but beyond the scope of the last 50 minute lecture of E77.
Perhaps we need one last 18 page lab…
By example, we partial overview of the strategy, minus the object oriented (user defined classes) wrapper.

3. Two more Matlab concepts
We need two more Matlab concepts before starting
subfunctions, also called Local functions
Cell array callbacks (as opposed to char callbacks last time)

4. Subfunctions
In a function m-file, it is legal to have two (or more) functions.
The first function is the main function
The second, third, etc are subfunctions
Each use the same syntax (original) for function declaration line
Name of subfunctions usually begins with LOCAL
The subfunctions are visible to
The main function in the same file
Any subfunctions in the same file
Convenience of functions without extra .m files
All variables in a subfunction are local
Like functions, use input and output arguments to pass variables “in” and “out” of the subfunction.
Subfunctions can called by their function_handle
The main function can access the function handle and pass that back to its caller…

5. Subfunctions Here is a simple example subex.m >> M = 9;
>> [R,K] = subex(M,P);
>> R
R = 15
>> feval(K,2,8)
ans = 4
function [A,H] = subex(B,C)
A = B + LocalFcn1(B,C); H
function Y = LocalFcn1(W,Q)
Y = sqrt(W*Q);
subex.m
Every subfunction can be accessed anywhere through its handle.

6. Cell array callbacks Create (for example) a pushbutton
PB = uicontrol(’style’,’pushb’);
and a function, ARG5.m
and a 1x4 cell array
cb = ’e77’ [100;10;1]};
Set the callback of the pushbutton to be the cell array.
set(PB,’Callback’,cb);
What happens when the button is pressed?
function ARG5(A1,A2,A3,A4,A5)
... % some code here

7. Cell array callbacks Setup is PB = uicontrol(’style’,’pushb’);
cb = ’e77’ [100;10;1]};
set(PB,’Callback’,cb);
Upon buttonpress, Matlab creates 2 variables, EventSrc and EventData, and executes an feval, without outputs
feval(cb{1},EventSrc,EventData,cb{2:end})
equivalently
ARG5(EventSrc,EventData,-14.1,’e77’,[100;10;1])
ARG5(A1, ,A ,A3 ,A4 ,A )
ARG5.m
function ARG5(A1,A2,A3,A4,A5)
...

8. Cell array callback, common mistake
Setup is
PB = uicontrol(’style’,’pushb’);
V = 17
cb = ’e77’ V};
set(PB,’Callback’,cb);
V = 18;
Now press button. What will the value of the 5th argument to the function ARG5 be?
Remember, Matlab will execute
feval(cb{1},EventSrc,EventData,cb{2:end})
Clarify: not actually the variable cb, but the contents of pushbutton’s CallBack property, get(PB,’Callback’))

9. PushButton/Counter ++ ++ 1 ++ 7
Let’s make a reusable object consisting of a
counter (initialized at 0)
pushbutton (to increment counter)
text display of counter value
Initial appearance
After one buttonpress
After 7 buttonpresses
User should also be able to program additional actions to occur after a button press.
pushbutton
frame
text
uicontrol ++ ++ 1 ++ 7

10. Overview of Tool Code function ToolH = fname(arg)
% Create objects which constitute the tool
% These are the “subobjects”
% Choose one subobject as the “tool handle” (ToolH)
% Create ToolState struct which holds tool “state”
% Hide ToolState in appdata of ToolH
% Set subobject properties, event callbacks to subfcns
% Input arg: ToolH (then subfcns can access ToolState)
function subf1(Esrc,Edata,ToolH)
% Ignore Esrc, Edata
% Retrieve ToolState (from appdata of ToolH)
% Do calcs, set properties of subobjects
% Update and replace ToolState (appdata of ToolH)
function subf2(Esrc,Edata,ToolH)
function subf3(Esrc,Edata,ToolH)

11. PushButton/Counter State
Graphics object is the counter/display
What information do we need to keep track of everything?
value of counter
handle of text display
function_handle that user wants to additionally execute when the value is incremented
Hence, tool state will be a structure with 3 fields
CntVal, integer counter value
DispHan, the handle of the text display uicontrol
IncCB, function_handle (plus additional arguments) of user defined increment callback ++ 1

12. function ToolHan = e77gui1(X,Y,IncCB)
FrameH = uicontrol('style','frame',...
'position',[X Y ]);
PlusH = uicontrol('style','pushbutton',...
'position',[X+5 Y ],'str','++');
DispH = uicontrol('style','text',...
'position',[X+50 Y ]);
ToolHan = DispH;
ToolState.DispHan = DispH;
ToolState.CntVal = 0;
ToolState.IncCB = IncCB;
setappdata(ToolHan,'ToolState',ToolState);
ToolHan});
set(DispH,'str',int2str(ToolState.CntVal));
function LOCALinc(ESrc, EData, TH)
TS = getappdata(TH,'ToolState');
TS.CntVal = TS.CntVal + 1;
set(TS.DispHan,'str',int2str(TS.CntVal));
setappdata(TH,'ToolState',TS);
if ~isempty(TS.IncCB)
feval(TS.IncCB{1},ESrc,EData,...
TH,TS.IncCB{2:end})
end
Create the objects that constitute the tool
Designate toolhandle
Create struct of Tool state (all relevant info)
Hide state in ToolHan
Set callback events & subobject properties
Retrieve ToolState
Do calculations, set subobject properties
Update ToolState
Run user callback if it exists, passing supplied arguments

13. function ToolHan = e77gui1(X,Y,IncCB)
FrameH = uicontrol('style','frame',...
'position',[X Y ]);
PlusH = uicontrol('style','pushbutton',...
'position',[X+5 Y ],'str','++');
DispH = uicontrol('style','text',...
'position',[X+50 Y ]);
ToolHan = DispH;
ToolState.DispHan = DispH;
ToolState.CntVal = 0;
ToolState.IncCB = IncCB;
setappdata(ToolHan,'ToolState',ToolState);
ToolHan});
set(DispH,'str',int2str(ToolState.CntVal));

14. function ToolHan = e77gui1(IncCB)
% Omitted Code
PlusH = uicontrol('style','pushbutton',...
ToolHan});
function LOCALinc(ESrc, EData, TH)
TS = getappdata(TH,'ToolState');
TS.CntVal = TS.CntVal + 1;
set(TS.DispHan,'str',int2str(TS.CntVal));
setappdata(TH,'ToolState',TS);
if ~isempty(TS.IncCB)
feval(TS.IncCB{1},ESrc,EData,TH,...
TS.IncCB{2:end})
end