[Newbies] Speed up image loading

[Felix Dorner]

Hi,

I am trying to write a Photo Manager Application, to learn Morphic and 
Squeak. So far I have created a custom Thumbnail morph 
"LabeledThumbnail" that is capable of holding a form and a label:

First I create forms like that:

form := (ImageReadWriter 
formFromFileNamed:'/home/felix/DCIM/101HPIMG/HPIM1625.JPG')

Thumbnails are then derived by (this is an instance method of 
LabeledThumbnail, not sure about the >> notation):

LabeledThumbnail>>form: aForm
    thumbnail ifNotNil: [ self removeMorph: thumbnail].
    thumbnail _ Thumbnail new.
    thumbnail maxWidth:150 minHeight:100.
    thumbnail makeThumbnailFromForm: aForm.
    self addMorph: thumbnail.

Now I created a new Class "ThumbnailBar", that displays a collection of 
LabeledThumbnails:

ThumbnailBar class>>newFromPhotoCollection: aPhotoCollection
    | tmp form |
    tmp _ self new.
    aPhotoCollection do: [ :entry |
                               form _ ImageReadWriter formFromFileNamed: 
entry.
                               tmp addMorph: (LabeledThumbnail 
newFromForm: form withLabel: entry) asMorph
                           ].
    ^ tmp

PhotoCollection is a bare list of filenames.

Obviously this is not complete, I want to add scrollbars etc. However, 
my current issue is speed. Doing a

col := PhotoCollection newFromDirectory: '/home/felix/DCIM'.
(ThumbnailBar newFromPhotoCollection: col) openInWorld

takes about way too long (minutes range) until the Thumbnail bar shows 
up (there are about 200 hi-res jpegs in the collection).

I guess that the most time is spent loading and scaling the images, so 
I'll probably cache the thumbs on disk. Another issue is easier and more 
intresting to me: I like to reduce the number of Morph objects. E.G. my 
"LabeledThumbnail" is a RectangleMorph that owns an ImageMorph and a 
StringMorph. I want to get rid of the submorphs and write my own drawing 
code. I have already seen how this is done, but am a little afraid of 
the redrawing/updating stuff. E.g. this confuses me already:

ImageMorph>>image: anImage
    self changed.
    image := anImage depth = 1
                ifTrue: [ColorForm mappingWhiteToTransparentFrom: anImage]
                ifFalse: [anImage].
    super extent: image extent

Intuitively the "changed" message should be send as the _last_ 
statement, not the first one. Can anyone explain?


Thanks,
Felix