[Scummvm-devel] Re: ScummVM

[Travis Howell]

From: "Max Horn" <max at quendi.de>
>> In the past (scumm/resource.cpp revision 1.93) you made findResource() 
>> and findResourceData() constant in ScummVM, was there any particular 
>> requirement for this change and would it be ok to change back ? some of 
>> the WizImage functions used by HE games need to alter the data. Check the 
>> commented out code in fillWizRect() of scumm/wiz_he.cpp for example, 
>> there are several other cases too (Which have not been commited yet).
>
> It would be possible to change it back -- there is no fundamental 
> technical issue prompting it to return read-only data.
>
> However, the way those methods are intended, you should never have to 
> write to data they return. It's more an API design decision than anything 
> else. The only place where the old code (before my change) ever needed to 
> write into this data was with the old code used to changing Scumm object 
> names -- that code directly hacked the object resources, like the original 
> engines did. Well, it was already a bad evil hack when they did it back 
> then (and it forced them to re-do the name change whenever the room was 
> reloaded, because these changes were of course not persistent). I think 
> it's no coincidence that in V6, they introduced the object name resource 
> to avoid this hack (and we basically use the same technique now to avoid 
> it in V1-V5 games, too).
>
> If you want to write to data returned by findResource() / 
> findResourceData(), then if I were you, I'd first question my design and 
> wonder: "Why do I have to do this? Do I really need to, or is there 
> another way?" Normally, you should only ever have to write to resource 
> data you created yourself (using createResource()), in which case you 
> already have a writeable pointer to the data anyway...
>
> Of course it's possible that in the HE games, this rule was changed, in 
> which case we could adapt. But I'd like to first learn a bit more as to 
> why exactly the change is required, i.e. what feat do you need to 
> accomplish? Maybe we can think of an alternate solution...

The image type resources used for WizImages in HE games often have multiple 
blocks (Checked through findWrappedBlock().in scumm/script_v72he.cpp). Some 
of the block types (i.e. TRNS) are optional, so not every resource will 
contain all blocks either. A few WizImage functions (i.e. processWizImage() 
case 6, fillWizRect() in scumm/wiz_he.cpp) alter the data of a single block 
of an image resource. Since the image type resources can use multiple 
blocks, it makes sense to just alter a single block, rather than try to 
reconstruct a fresh altered resource block by block.
I have just added HE game specific version of findResource/findResourceData 
(With he prefix) for now, since blocks are only altered through calls to 
findWrappedBlock().