Volume Number:		5
Issue Number:		2
Column Tag:		Mousehole report

Mousehole Report

By Rusty Hodge & Larry Nedry, Mousehole BBS

From: thecloud (Ken Mcleod, La Habra, CA)

Subject: ScrollRect()

I’d like to be able to use ScrollRect to cause one bitmap to scroll down *into* a window, as the contents of that window are simultaneously scrolling down out of the visRgn. Trouble is, the update region gets filled with the port’s bkPat (white) by ScrollRect, and this results in a “flash of white” before I can get the area redrawn. Can anyone point out a strategy for accomplishing this “smoothly”? I’m currently doing something like this:

for (i=1; i <= appropriate_multiple_of_inc; i++) {
ScrollRect(&theRect, 0, inc, myRgnHandle);
ScrollRect(&anotherRect, 0, inc, myRgnHandle);   
Draw_Stuff_In_anotherRect()  }

but I’m sure I just need someone to kick me in the right direction!

From: rdclark (Richard Clark, Tustin, CA)

Subject: A kick in the right direction

Look at the articles by Scott Boyd (“The MacHax Group”) in the past 2 years of MacTutor -- they show how to do some pretty weird stuff with off-screen bitmaps and the like, including a trick to get rid of the “flash of white” when moving/updating a window.

From: lsr (Larry Rosenstein, Cupertino, CA)

Subject: Re: ScrollRect()

The best thing to do is to create an offscreen bitmap and use CopyBits to draw the bitmap on the screen in its proper position. If I understand your application correctly, you want to smoothly change from one image to the other. In that case, you would need to have the combined image offscreen, and use a series of CopyBits calls to draw the appropriate rectangle on the screen. (You would start out by copying the entire first image, then most of the first and part of the second, etc.)

CopyBits works the fastest when Quickdraw doesn’t have to shift every scan line. If you can control the position of the window on the screen, then you should make sure that its global screen position is a multiple of 16 (or 32 on a Mac II).

There probably is a way to prevent ScrollRect from erasing things, but the resulting effect wouldn’t be acceptable either. You would notice the delay between the ScrollRect and the redraw.

From: thecloud (Ken Mcleod, La Habra, CA)

Subject: Re: ScrollRect()

It always comes down to CopyBits in the end! Thanks...

From: robert (Rob Anthony, Chicago, IL)

Subject: MacIntalk

Check out APDA (Apple Programmers and Developers Assoc., in Renton, WA). They had -- in their ‘Curiosity Shoppe’ section -- the MacinTalk Development Package v. 1.31. It has docs and tools for using MacinTalk (they say). I don’t have it, so I can’t give any personal experience, but the APDA folks should be able to answer your questions. Need to be an APDA member to order; about $20 a year for that, but well worth it for the Mac programmer.

From: rhyman (Richard A. Hyman, Morrison, CO)

Subject: Desktop File

Prior to release 5 of the system software, the invisible Desktop file contained a resource called FOBJ that contained info on the open directories, view-by type information, and so on. The Finder used this info when starting up after quitting an application or during the boot-up. The FOBJ resource no longer exists with the newer system releases except for 400k MFS volumes. Does anyone know how this information is stored under system releases 5 & 6??

From: lsr (Larry Rosenstein, Cupertino, CA)

Subject: Re: Dialog Hook Procedure Problem

The problem is that you are using a local procedure, and the ROM is expecting a procedure at the top level. This is true of all the ROM routines that expect a pointer to a procedure. (In Pascal, nested procedures expect to find an extra parameter on the stack, which is a pointer to the enclosing stack frame.)

From: mwatts (Michael Watts, Santa Clara, CA)

Subject: limit on scroll bar value

Hi. I am new to the mousehole and have spent an informative session catching up. There is one question which I need help on if someone would be so kind.

In the app which I am writing, I have to deal with data which contains more than 32k points. I want to scroll through this data using a scroll bar, however the max value is an integer (opps). Even if I write my own control, in IM V I-333 the upper value for the CNTL resource is 2 bytes (not enough). I have kludged a fix by breaking the stream into 32k point sections, however this adds another control to my window and complexity to the program.

Does anyone know how to get around this problem, and if so how?

From: thotpolc (Bill Evans, Irvine, CA)