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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
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