.TH g.pnmcomp 1grass "" "GRASS 6.4.4" "Grass User's Manual"
.SH NAME
\fI\fBg.pnmcomp\fR\fR  - Overlays multiple PPM image files
.SH KEYWORDS
general, gui
.SH SYNOPSIS
\fBg.pnmcomp\fR
.br
\fBg.pnmcomp help\fR
.br
\fBg.pnmcomp input\fR=\fIstring\fR[,\fIstring\fR,...]  [\fBmask\fR=\fIstring\fR[,\fIstring\fR,...]]   [\fBopacity\fR=\fIfloat\fR[,\fIfloat\fR,...]]  \fBoutput\fR=\fIstring\fR  [\fBoutmask\fR=\fIstring\fR]  \fBwidth\fR=\fIinteger\fR \fBheight\fR=\fIinteger\fR  [\fBbackground\fR=\fIstring\fR]   [\-\-\fBverbose\fR]  [\-\-\fBquiet\fR] 
.SS Parameters:
.IP "\fBinput\fR=\fIstring[,\fIstring\fR,...]\fR" 4m
.br
Names of input files
.IP "\fBmask\fR=\fIstring[,\fIstring\fR,...]\fR" 4m
.br
Names of mask files
.IP "\fBopacity\fR=\fIfloat[,\fIfloat\fR,...]\fR" 4m
.br
Layer opacities
.IP "\fBoutput\fR=\fIstring\fR" 4m
.br
Name of output file
.IP "\fBoutmask\fR=\fIstring\fR" 4m
.br
Name of output mask file
.IP "\fBwidth\fR=\fIinteger\fR" 4m
.br
Image width
.IP "\fBheight\fR=\fIinteger\fR" 4m
.br
Image height
.IP "\fBbackground\fR=\fIstring\fR" 4m
.br
Background color
.PP
.SH DESCRIPTION
(culled from the mailing list)
.br
\fC
.DS
.br
From: Glynn Clements 
.br
Subject: Re: [GRASS5] Re: [GRASSLIST:10403] Transparency added
.br
Date: Sun, 19 Feb 2006 20:17:59 +0000
.br
.br
g.pnmcomp isn't meant for end users. It's an internal tool for use by
.br
a Tcl/Tk GUI.
.br
.br
In essence, g.pnmcomp generates a PPM image by overlaying a series of
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PPM/PGM pairs (PPM = RGB image, PGM = alpha channel).
.br
.br
The intention is that d.* programs will emit PPM/PGM pairs (by way of
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the PNG-driver code being integrated into libraster). The GUI will
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manage a set of layers; each layer consists of the data necessary to
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generate a PPM/PGM pair.
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Whenever the layer "stack" changes (by adding, removing, hiding,
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showing or re-ordering layers), the GUI will render any layers for
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which it doesn't already have the PPM/PGM pair, then re-run g.pnmcomp
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to generate the final image (just redoing the composition is a lot
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faster than redrawing everything).
.br
.br
A C/C++ GUI would either have g.pnmcomp's functionality (image
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composition) built-in, or would use the system's graphics API to
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perform composition (for translucent layers, you would need OpenGL or
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the Render extension, or something else which supports translucent
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rendering).
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Tk doesn't support transparent (masked) true-colour images (it does
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support transparent GIFs, but that's limited to 256 colours), and an
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image composition routine in Tcl would be unacceptably slow, hence
.br
the existence of g.pnmcomp.
.br
.DE
\fR
.SH AUTHOR
Glynn Clements
.PP
\fILast changed: $Date: 2011-11-08 12:29:50 +0100 (Tue, 08 Nov 2011) $\fR
.PP
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.PP
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