patch for some acme scrolling issues that've been bugging me
for years.

1) when middle-button scrolling to the bottom of a long
document, acme doesn't go right to the end - there's a bit
more of the document left below.

2) acme constrains the mouse to remain within the boundaries
of the scrollbar. i find this unnecessary and sometimes unhelpful.

3) clicking with b1 or b3 on the very top line's-worth
of the scrollbar does nothing, meaning that it's essentially
dead space, and also that it's awkward to scroll
very small (one or two line) windows.

one gratuitous change: a piece of code from optionally
using fixed-point arithmetic to use a vlong;
it looks simpler that way and the overhead
is negligible by my reckoning.

YMMV.

Notes:
Thu Mar 17 23:18:08 EST 2005 rsc
    i picked up 1) and the vlong change.
    i changed 2) so that the mouse can't get out of the scroll bar ever,
    	but kept the boundaries.
    i did not pick up 3) at all.  you might convince me to
    special case clicking on the top line, but changing the
    click semantics is too big a change, and it destroys the
    very nice explanation that 1-clicking a line brings the
    top line to where you clicked, and 3-clicking brings the
    current line to the top.
    
    i changed cols.c so that you can 1 or 3 click in the space
    below the bottom window, in case the mouse ends up there 
    after a 2-scroll.
    


Reference: /n/sources/patch/applied/acmescroll
Date: Tue Mar 15 02:35:27 CET 2005
Reviewed-by: rsc

--- /sys/src/cmd/acme/scrl.c	Tue Mar 15 02:15:53 2005
+++ /sys/src/cmd/acme/scrl.c	Tue Mar 15 02:15:40 2005
@@ -112,53 +112,42 @@
 
 	s = insetrect(t->scrollr, 1);
 	h = s.max.y-s.min.y;
-	x = (s.min.x+s.max.x)/2;
 	oldp0 = ~0;
 	first = TRUE;
 	do{
 		flushimage(display, 1);
-		if(mouse->xy.x<s.min.x || s.max.x<=mouse->xy.x){
-			readmouse(mousectl);
-		}else{
-			my = mouse->xy.y;
-			if(my < s.min.y)
-				my = s.min.y;
-			if(my >= s.max.y)
-				my = s.max.y;
-			if(!eqpt(mouse->xy, Pt(x, my))){
-				moveto(mousectl, Pt(x, my));
-				readmouse(mousectl);		/* absorb event generated by moveto() */
-			}
-			if(but == 2){
-				y = my;
-				if(y > s.max.y-2)
-					y = s.max.y-2;
-				if(t->file->nc > 1024*1024)
-					p0 = ((t->file->nc>>10)*(y-s.min.y)/h)<<10;
-				else
-					p0 = t->file->nc*(y-s.min.y)/h;
-				if(oldp0 != p0)
-					textsetorigin(t, p0, FALSE);
-				oldp0 = p0;
-				readmouse(mousectl);
-				continue;
-			}
-			if(but == 1)
-				p0 = textbacknl(t, t->org, (my-s.min.y)/t->font->height);
-			else
-				p0 = t->org+frcharofpt(t, Pt(s.max.x, my));
+		my = mouse->xy.y;
+		if(my < s.min.y)
+			my = s.min.y;
+		if(my >= s.max.y)
+			my = s.max.y;
+		if(but == 2){
+			y = my;
+			p0 = (vlong)t->file->nc * (y-s.min.y) / h;
+			if(p0 >= t->q1)
+				p0 = textbacknl(t, p0, 2);
 			if(oldp0 != p0)
-				textsetorigin(t, p0, TRUE);
+				textsetorigin(t, p0, FALSE);
 			oldp0 = p0;
-			/* debounce */
-			if(first){
-				flushimage(display, 1);
-				sleep(200);
-				nbrecv(mousectl->c, &mousectl->Mouse);
-				first = FALSE;
-			}
-			scrsleep(80);
+			readmouse(mousectl);
+			continue;
+		}
+		my += t->font->height;
+		if(but == 1)
+			p0 = textbacknl(t, t->org, (my-s.min.y)/t->font->height);
+		else
+			p0 = t->org+frcharofpt(t, Pt(s.max.x, my));
+		if(oldp0 != p0)
+			textsetorigin(t, p0, TRUE);
+		oldp0 = p0;
+		/* debounce */
+		if(first){
+			flushimage(display, 1);
+			sleep(200);
+			nbrecv(mousectl->c, &mousectl->Mouse);
+			first = FALSE;
 		}
+		scrsleep(80);
 	}while(mouse->buttons & (1<<(but-1)));
 	while(mouse->buttons)
 		readmouse(mousectl);