afterimage.html

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## libAfterImage/libAfterImage

NAME

     libAfterImage

SYNOPSIS

     Generic imaging library originally designed for AfterStep X Window
     Manager.

PURPOSE

     libAfterImage is the imaging library implemented for AfterStep
     X Window Manager. It has been generalized to be suitable for any
     application in need of robust graphics engine.

     It provides facilities for loading images from files of different
     formats, compressed in memory storage of images, scaling,
     tinting/shading, flipping and superimposition of arbitrary number of
     images over each other. In addition it allows for linear gradients
     drawing, and antialiased/smoothed text drawing using both  FreeType
     library and X Window fonts.

     Primary goals of this library are to achieve exceptional quality of
     images and text, making code fast and small at the same time.
     Additional steps are taken to compensate for screen colordepth
     limitation, and different error diffusion algorithms are used to
     provide for smooth images even in low colordepth modes.

HISTORY

     libAfterImage has been implemented as an attempt to address several
     issues. First one, and most important is that X Window System
     completely lacks any tools for image manipulation, except for very
     rudimentary operations. With Introduction of Render extentions in
     XFree86 4.0 that situation is changing, but still is far from
     perfect. There need is therefore to implement client side image
     manipulation. That inturn creates a problem of image data transfer
     between Server and client.

     To avoid that full-time image storage on the client side is needed.
     Which is memory extensive. So there appears to be a need for some
     in-memory compression.

     On the other side there is an image quality issue. Its easy to write
     a scaling function by simply dropping out or duplicating pixels,
     but quality is awfull. What is needed is very fast
     averaging/interpolation code. That brings us to the issue of 8 bits
     per channel. Add two pixels together and you get overflow. So all the
     math has to be performed in different colorspace and then converted
     back. On the other side, such a conversion may discard valuable bits,
     so some compensation method has to be implemented.

     On the text drawing side of things, there are numerous problems just
     as well. Native X fonts look ugly as soon as you try to show any
     decently sized text. That is supposed to be solved with said Render
     extensions to XFree86, but as experiense has shown, things aren't as
     easy as it looks, besides one wants his app to run well under any X
     Server. FreeType library provides a solution, but not always
     available. Another problem is that if you keep all your images on the
     client side, you want to draw text on client side as well.

     The solution is to provide transparent interface that could use both
     X fonts and FreeType, cache glyphs on the client side and possibly
     perform smoothing of ugly X fonts.

     There is no library solving all this problems in one fell swoop,
     except for monstrous ones, like ImLib.

     Hence libAfterImage has come to life.

DESCRIPTION

     libAfterStep provides sevarl facilities.

     1. X Visual abstruction layer via ASVisual. This layer handles color
     management, transfer of data to and from X Server, and other screen
     related stuff.

     2. Scanline handling facility via ASScanline. ASScanline is the most
     widely used structure since image handling is implemented on
     per-scanline basis.

     3. Image storage, trasformation and rendering via ASImage. ASImage
     provides for generic container used for any image or text
     manipulation. It incorporates such a robust facilities as in-memory
     RLE compression, separate channel storage of 4 channels ( Alpha, Red,
     Green, and Blue ) with 8 bit per channel.

     4. Simplified font handling facility via ASFont and ASFointManager.
     All the font handling is done using ASFont structure, no matter what
     type of font is used. Any font supported by X11 and FreeType can be
     used.

     5. Transparent image file reading for many different formats. Included
     built-in XPM reading code and XCF ( GIMP's native format ).
     Overall supported:
     via external libraries :
     XPM, JPEG, PNG, TIFF, GIF
     via built in code :
     XPM, XCF, PNM, PPM, BMP, ICO, CUR
     Note that XPM can be supported both via built-in code or via libXpm,
     depending on compilation configuration.
     Actuall image file format is autodetected from the file contents -
     file name extention is not used and can be anything at all.

USES

     libAfterBase - AfterStep basic functionality library. That Includes
     Hash tables, file search methods, message output, generic types.
     However effort has been made to allow for standalone configuration as
     well. If libAfterBase is not found at compilation time - libAfterImage
     will use extract from libAfterBase included with libAfterImage.

SEE ALSO

     Examples
     API Reference

TODO

     Implement support for Targa and PCX image format and maybe some other
     formats as well.

     Implement complete support for I18N internationalization.

     Implement color<->pixel conversion for all colordepths.

AUTHOR

     Sasha Vasko <sashav at sprintmail dot com>

## libAfterImage/Examples

EXAMPLE

     ASView  - image loading from the file and displaying in window.
     ASScale - image loading from file and scaling to arbitrary size.
     ASTile  - image loading from file, tiling and tinting to arbitrary
               size and color.
     ASMerge - imgae loading and merging with another image.
     ASGrad  - mutlipoint gradient drawing.
     ASFlip  - image loading from file and rotation.
     ASText  - trexturized semitransparent antialised text drawing.

SEE ALSO

     API Reference

## libAfterImage/API

CHILDREN

     Headers :
              asvisual.h, blender.h, asimage.h, import.h, asfont.h
     Structures :
              ColorPair
              ASScanline
              ASVisual
              ASImage
              ASImageBevel
              ASImageDecoder
              ASImageOutput
              ASImageLayer
              ASGradient
              ASFontManager
              ASFont
              ASGlyph
              ASGlyphRange
     Functions :
       ASScanline handling:
            prepare_scanline(), free_scanline()

       ASVisual initialization :
            query_screen_visual(), setup_truecolor_visual(),
            setup_pseudo_visual(), setup_as_colormap(),create_asvisual(),
            destroy_asvisual()

       ASVisual encoding/decoding :
            visual2visual_prop(), visual_prop2visual()

       ASVisual convenience functions :
            create_visual_window(), create_visual_pixmap(),
            create_visual_ximage()

       Colorspace conversion :
              rgb2value(), rgb2saturation(), rgb2hue(), rgb2luminance(),
              rgb2hsv(), rgb2hls(), hsv2rgb(), hls2rgb().

       merge_scanline methods :
              alphablend_scanlines(), allanon_scanlines(),
              tint_scanlines(), add_scanlines(), sub_scanlines(),
              diff_scanlines(), darken_scanlines(), lighten_scanlines(),
              screen_scanlines(), overlay_scanlines(), hue_scanlines(),
              saturate_scanlines(), value_scanlines(),
              colorize_scanlines(), dissipate_scanlines().

       ASImage handling :
              asimage_init(), asimage_start(), create_asimage(),
              destroy_asimage()

       Encoding :
              asimage_add_line(),   asimage_add_line_mono(),
              asimage_print_line()

       Decoding
              start_image_decoding(), stop_image_decoding()

       Output :
              start_image_output(), set_image_output_back_color(),
              toggle_image_output_direction(), stop_image_output()

       X11 conversions :
              ximage2asimage(), pixmap2asimage(), asimage2ximage(),
              asimage2mask_ximage(), asimage2pixmap(), asimage2mask()

       Transformations :
              scale_asimage(), tile_asimage(), merge_layers(), make_gradient(),
              flip_asimage()

       Import :
              file2ASImage(), file2pixmap()

       Text Drawing :
              create_font_manager(), destroy_font_manager(),
              open_freetype_font(), open_X11_font(), get_asfont(),
              destroy_font(), print_asfont(), print_asglyph(),
              draw_text()