g.pnmcomp.1grass man page

g.pnmcomp — Overlays multiple PPM image files.

Keywords

general, display

Synopsis

g.pnmcomp
g.pnmcomp --help
g.pnmcomp input=name[,name,...]  [mask=name[,name,...]]   [opacity=float[,float,...]]  output=name  [output_mask=name]  width=integer height=integer  [bgcolor=name]   [--overwrite]  [--help]  [--verbose]  [--quiet]  [--ui]

Flags

--overwrite

Allow output files to overwrite existing files

--help

Print usage summary

--verbose

Verbose module output

--quiet

Quiet module output

--ui

Force launching GUI dialog

Parameters

input=name[,name,...] [required]

Name of input file(s)

mask=name[,name,...]

Name of input mask file(s)

opacity=float[,float,...]

Layer opacities

output=name [required]

Name for output file

output_mask=name

Name for output mask file

width=integer [required]

Image width

height=integer [required]

Image height

bgcolor=name

Background color
Either a standard color name or R:G:B triplet

Description

g.pnmcomp isn’t meant for end users. It’s an internal tool for use by wxGUI.

In essence, g.pnmcomp generates a PPM image by overlaying a series of PPM/PGM pairs (PPM = RGB image, PGM = alpha channel).

Notes

The intention is that d.* modules will emit PPM/PGM pairs (by way of the PNG-driver code being integrated into Display Library). The GUI will manage a set of layers; each layer consists of the data necessary to generate a PPM/PGM pair. Whenever the layer "stack" changes (by adding, removing, hiding, showing or re-ordering layers), the GUI will render any layers for which it doesn’t already have the PPM/PGM pair, then re-run g.pnmcomp to generate the final image (just redoing the composition is a lot faster than redrawing everything).

A C/C++ GUI would either have g.pnmcomp’s functionality (image composition) built-in, or would use the system’s graphics API to perform composition (for translucent layers, you would need OpenGL or the Render extension, or something else which supports translucent rendering).

Tk doesn’t support transparent (masked) true-colour images (it does support transparent GIFs, but that’s limited to 256 colours), and an image composition routine in Tcl would be unacceptably slow, hence the existence of g.pnmcomp.

See Also

g.cairocomp

Author

Glynn Clements

Last changed: $Date: 2013-01-15 07:12:43 -0800 (Tue, 15 Jan 2013) $

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