text: /*
   * This file is part of the UCB release of Plan 9. It is subject to the license
   * terms in the LICENSE file found in the top-level directory of this
   * distribution and at http://akaros.cs.berkeley.edu/files/Plan9License. No
   * part of the UCB release of Plan 9, including this file, may be copied,
   * modified, propagated, or distributed except according to the terms contained
   * in the LICENSE file.
   */
  
  #include <u.h>
  #include <lib9.h>
  #include <draw.h>
  #include <memdraw.h>
  #include <memlayer.h>
  
  Memimage*
  memlalloc(Memscreen *s, Rectangle screenr, Refreshfn refreshfn, void *refreshptr,
  	  uint32_t val)
  {
  	Memlayer *l;
  	Memimage *n;
  	static Memimage *paint;
  
  	if(paint == nil){
  		paint = allocmemimage(Rect(0,0,1,1), RGBA32);
  		if(paint == nil)
  			return nil;
  		paint->flags |= Frepl;
  		paint->clipr = Rect(-0x3FFFFFF, -0x3FFFFFF, 0x3FFFFFF, 0x3FFFFFF);
  	}
  
  	n = allocmemimaged(screenr, s->image->chan, s->image->data);
  	if(n == nil)
  		return nil;
  	l = malloc(sizeof(Memlayer));
  	if(l == nil){
  		free(n);
  		return nil;
  	}
  
  	l->screen = s;
  	if(refreshfn)
  		l->save = nil;
  	else{
  		l->save = allocmemimage(screenr, s->image->chan);
  		if(l->save == nil){
  			free(l);
  			free(n);
  			return nil;
  		}
  		/* allocmemimage doesn't initialize memory; this paints save area */
  		if(val != DNofill)
  			memfillcolor(l->save, val);
  	}
  	l->refreshfn = refreshfn;
  	l->refreshptr = nil;	/* don't set it until we're done */
  	l->screenr = screenr;
  	l->delta = Pt(0,0);
  
  	n->data->ref++;
  	n->zero = s->image->zero;
  	n->width = s->image->width;
  	n->layer = l;
  
  	/* start with new window behind all existing ones */
  	l->front = s->rearmost;
  	l->rear = nil;
  	if(s->rearmost)
  		s->rearmost->layer->rear = n;
  	s->rearmost = n;
  	if(s->frontmost == nil)
  		s->frontmost = n;
  	l->clear = 0;
  
  	/* now pull new window to front */
  	_memltofrontfill(n, val != DNofill);
  	l->refreshptr = refreshptr;
  
  	/*
  	 * paint with requested color; previously exposed areas are already right
  	 * if this window has backing store, but just painting the whole thing is simplest.
  	 */
  	if(val != DNofill){
  		memsetchan(paint, n->chan);
  		memfillcolor(paint, val);
  		memdraw(n, n->r, paint, n->r.min, nil, n->r.min, S);
  	}
  	return n;
  }
  