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+			GUI WORK NOTES - November 1993
+
+TODO
+
+    enhance mapping code in Gterm widget (see below)
+    ximtool enhancements
+	locator, magnifier, control panel, socket support, etc.
+    clean up xgterm
+			    - beta release -
+    obm enhancements
+	more gui bindings, new widgets
+    imbrowse, movie demos
+    obm documentation
+
+
+1. MAPPINGS
+
+    src rect -> dst rect
+
+    construct pixel level mappings for each axis
+	this source pixel maps to these destination pixels
+	this destination pixel maps to these source pixels
+
+    in general (zoom/dezoom) the mapping is not one-to-one
+    when one source pixel maps to several destination pixels, pixel replication
+	is used to draw the destination pixels
+    when one destination pixel maps to several source pixels the destination
+	pixel value may be computed by any of several different techniques
+
+    major cases
+
+	mapping is one-to-one
+	mapping is one-to-many	 zoom mapping (pixel replication)
+	mapping is many-to-one	 dezoom mapping (antialias)
+
+    antialiasing techniques
+
+	nearest			nearest neighbor
+	bilinear		2x2 distance weighted sum
+
+	area			included area weighted sum
+	lowpass			convolve followed by nearest neighbor
+	gaussian		gaussian weighted sum over NxN pixels
+
+	All of these involve projecting the center of each destination
+	pixel back into the source raster.  The antialiasing technique
+	applied to the NxN neighborhood around the source coordinate
+	then determines the value of the destination pixel.
+
+	Reasonable choices
+	    nearest		fastest, but no antialiasing
+	    bilinear		mininum smoothing if mag < 2
+	    lowpass		not bad for mag < 3
+	    area,gaussian	best for large demagnification ratios
+
+	Nearest and bilinear (NB) are mutually exclusive and may be selected
+	independently of area, lowpass, or gaussian (ALG).  If one of ALG is
+	selected and one of NB is also selected, the antialias code will use
+	one or the other technique depending upon the scaling.  If one of NB
+	or ALG is selected but not both, the specified technique will be
+	used regardless of the scaling.
+
+    setMapping should compute scaling maps
+    copyRaster uses these to compute the destination pixels
+    refreshRaster uses these to compute region of source rect
+
+    computing a mapping
+	rasterop
+	src rect, dst rect
+	coordinate types
+	flags: enabled, defined, refresh
+	scaling type (unitary, zoom, dezoom)
+	backprojection array maps dst pixel to src pixel
+	    integer mapping (1-1, zoom):	pixel number, integer
+	    antialias mapping (dezoom):		pixel center, floating
+	extent array gives range of dst pixels affected by a given
+	    src pixel - 2 values per source pixel
+	xscale, yscale (forward direction)
+
+
+2. PSEUDOCODE
+
+procedure copyRaster (src, src rect, dst, dst rect)
+begin
+	create temporary mapping
+	refresh entire mapping
+end
+
+procedure writePixels (dst, dst rect, pixels)
+begin
+	modify source raster pixels
+	update any mappings that intersect source rect
+end
+
+procedure setMapping (mapping, mapping data)
+begin
+	if (new mapping, mapping not enabled, or refreshNone set)
+	    merely store new mapping
+	else {
+	    # Edit and refresh a mapping.
+	    if (scale is unchanged) {
+		compare old, new mappings
+		refresh only changed regions
+		store new mapping
+	    } else {
+		store new mapping
+		refresh entire mapping
+	    }
+	    refresh any uncovered regions
+	}
+
+	if (mapping is one-to-one) {
+	    scaling = none
+	} else if (mapping is one-to-many) {
+	    compute integer dst->src scaling maps
+	    scaling = zoom
+	} else if (mapping is many-to-one) {
+	    compute array of back projected dst->src pixel centers
+	    scaling = dezoom
+	}
+end
+
+procedure refresh_source (mapping, source rect)
+begin
+	compute destination rect
+	refresh_destination (mapping, destination rect)
+end
+
+procedure refresh_destination (mapping, destination rect)
+begin
+	set clip mask in GC to prevent drawing into any mapped regions
+	which cover the mapping being refreshed
+
+	# Special case of pixmap to pixmap copy with no scaling.
+	if (no scaling and src is pixmap and dst is pixmap) {
+	    do direct XCopyArea
+	    goto done
+	}
+
+	# Get source ximage.
+	if (src is pixmap) {
+	    xin = ximage returned by XGetImage
+	    set del_xin flag
+	} else
+	    xin = src ximage
+
+	# Special case of ximage to pixmap copy with no scaling.
+	if (no scaling and dst is pixmap) {
+	    do XPutImage to write xin to dst pixmap
+	    goto done
+	}
+
+	# Get destination ximage.
+	if (dst is pixmap) {
+	    xout = create an ximage of the required size
+	    set del_xout flag
+	} else
+	    xout = dst ximage
+
+	# Copy src ximage to dst ximage.
+	if (mapping is one to one) {
+	    copy region of xin to xout without scaling
+
+	} else if (mapping is one to many - zoom) {
+	    for (each line of destination)
+		if (mapped src Y same as previous line)
+		    copy previous dst line
+		else {
+		    for (each destination pixel)
+			pixel = get pixel from xin using dst->src map
+		}
+
+	} else (mapping is many to one - dezoom) {
+	    if (function is lowpass) {
+		compute lowpass xin
+		set function to nearest neighbor
+	    }
+
+	    for (each line of destination)
+		for (each destination pixel)
+		    pixel = antialias_function (src, x, y, nx, ny)
+	}
+
+	if (dst is pixmap)
+	    do XPutImage to write xout to dst pixmap
+
+	clear clip mask in GC
+end
+	
+
+