The past week we’ve been busy working on optimizations on the 68k CPU and various improvements to the toolbox API. One of the improvements has been adding support for Apple’s MacApp MethodDispatch routine, which is used by Object Pascal and C+- (yes, that’s “C plus minus”, Apple’s proprietary C++ version which was briefly out before official C++ came to Mac). Basically, MethodDispatch is the virtual function table dispatcher commonly seen in C++ programs, but instead of being bundled in the application, it is actually implemented by the operating system as a toolbox trap – although with special calling convention, which cannot be called directly through A-line traps, but needs to be invoked through jump from 68k code. It handles selecting the correct implementation for class functions which can be inherited and overridden.

With the new MacApp method dispatching support, we should now be able to try running any MacApp-based applications – one cool such application, which is written in Objective-Pascal, is the first version of Adobe Photoshop:

Most of the dialog boxes appear to display (almost) correctly, although color picker, text input and popup menu support are missing so there’s little that can be done here:

And just to test out how it works, we did a quick “Hello world” drawing using Photoshop drawing tools inside MACE:

Although implementing the method dispatching routine was fairly trivial, some time was taken by other features used by Photoshop, such as crude International Utilities/Script Manager support, PrGlue dispatcher for printing (or as in current case, telling application that printers are not available), proper Gestalt support, and various bug fixes even to some fairly low-level things as handling of empty regions in UnionRgn calls, rewriting the 80-bit “Extended” floating-point format conversion in SANE, etc… A few other test applications did benefit of those additions, but we’ll post more about them later!

Ps. In case you are interested how MacApp-based application code looks like, the original Object Pascal source code for the first Mac Photoshop was at some time ago published as open-source and is available on github: https://github.com/amix/photoshop