Image manipulation library

         File: LibImageManip.zip
       Author: Edmund Vermeulen <edmundv@xs4all.nl>
      Release: 1.0.0 (Nov 18th 1999)
Compatibility: BeOS R4 for PowerPC and Intel
     Location: contrib/libraries
  Description: Image manipulation library
        Notes: Public domain

• Introduction
• The bitmap accessor class
• The add-on interface
• The application interface
• Standard io extensions
• History
• Installation
• Public domain

LibImageManip is my attempt at creating a library for image manipulation add-ons that is simple to use. It is modelled after, and based on, the datatypes library (now the translation kit) by Jon Watte.

The library basically supports two kinds of add-ons, known as manipulators and converters.

Manipulators

A manipulator add-on takes a source bitmap and then manipulates it any way it wants. Examples would be: gamma correct, twirl, ripple, oil paint, negative, flip horizontal, etc.

Converters

A converter add-on takes a source bitmap and then converts it to a new bitmap. Examples would be: scale, dither to 8-bit, rotate 90 degrees, crop, etc. Basically anything that needs a different size or color depth.

The library and its add-on interface are designed to be as simple as possible in order to encourage anyone to create add-ons or use the library in his/her applications. The library is completely free and comes with full source code.

The bitmap accessor class

The image manipulation library uses a proxy class for accessing bitmaps. This has several advantages over directly using the BBitmap class:

• The data doesn't have to be in the BBitmap format.
• Not all bitmap data has to be in memory at the same time.
• Progressive display is possible by sending messages from within the accessor for the areas that have been changed.

The proxy class is an abstract base class that looks like this:

  class BitmapAccessor
  {
  public:
      virtual ~BitmapAccessor();
      virtual bool IsValid() = 0;
      virtual bool CreateBitmap(BRect bounds, color_space space) = 0;
      virtual BRect Bounds() = 0;
      virtual color_space ColorSpace() = 0;
      virtual float BytesPerPixel(); 
      virtual void *AccessBits(BRect area, int32 *rowBytes) = 0;
      virtual void BitsNotChanged() = 0;
  };

The IsValid(), Bounds(), and ColorSpace() functions work the same as the equivalent functions in the BBitmap class. Beware that Bounds() may return a rectangle that is not positioned at (0, 0).

The CreateBitmap() function is called from within the Convert() function by a converter add-on to create the destination bitmap.

The BytesPerPixel() function is used to get the number of bytes in a single pixel. If the pixel size is larger than you would expect then you should simply skip the extra bytes at the end to get to the next pixel. This can be the case for 'multi-channel' bitmaps, where several channels of data are interleaved. For example, when accessing only the blue part of a 32-bit bitmap as if it was an 8-bit grayscale bitmap. For monochrome bitmaps the number of bytes per pixel is 1/8th. These bitmaps are special. For instance, you can only access the bits on their natural alignment, and not in the middle of a chunk.

With the AccessBits() function you gain access to the raw data of a certain area of the bitmap. The number of bytes to skip to get to the next row of pixels is returned in rowBytes. The pointer returned by AccessBits() will remain valid until another call to AccessBits() or to the destructor is made. For efficienscy reasons you should keep the requested area small.

For applications there is a class implemented in the library for accessing BBitmaps called BBitmapAccessor.

The add-on interface

Here is a list of all exported data and functions of an image manipulation add-on.

  const char addonName[];  /* required, C string, ex "Gamma Correct" */
  const char addonInfo[];  /* required, descriptive C string, ex "Makes images brighter. Written by Slartibardfast." */
  const char addonCategory[]; /* optional, C string, ex "Color" */
  int32 addonVersion;  /* required, integer, ex 100 */

  status_t Manipulate(
      BitmapAccessor *sourceBitmap,
      BMessage *ioExtension,        /* can be NULL */
      bool checkOnly);

  status_t Convert(
      BitmapAccessor *sourceBitmap,
      BitmapAccessor *destBitmap,   /* call CreateBitmap() on this */
      BMessage *ioExtension,        /* can be NULL */
      bool checkOnly);

  status_t MakeConfig(  /* optional */
      BMessage *ioExtension,        /* can be NULL */
      BView **outView);

  status_t GetConfigMessage(  /* optional */
      BMessage *ioExtension,
      BMessage *ioCapability);

The addonName, addonInfo, addonCategory, and addonVersion are exported data that contain user accessable information about the add-on.

The Manipulate() and Convert() functions are where the real work is done. Depending on which function an add-on exports, it is considered to be an image manipulator or image converter. Both functions can be called in normal or in 'check-only' mode. This last mode is used to ask an add-on if it supports a certain source bitmap and io extension. The add-on should return B_NOT_ALLOWED if it doesn't.

Both the Manipulate() and Convert() functions take a pointer to a source bitmap accessor. The Convert() function also take a pointer to an empty bitmap accessor object on which it will call CreateBitmap() to create the destination bitmap. The ioExtension argument is optional, and may be ignored by the add-on.

The ioExtension message can be used for passing add-on specific configuration settings as explained below. It can also be used to, for example, ask the add-on to only affect a certain rectangle instead of the whole bitmap. Some standard io extensions are defined for this purpose. The add-on should add the io extensions that it supports to the ioCapability message in its GetConfigMessage() function.

The last two functions are optional. MakeConfig() allows the add-on to create a BView with controls to let the user configure the add-on's settings. GetConfigMessage() is used to get the current settings and supported capabilities from the add-on. The settings are added to the ioExtension message. This message can be stored and passed back to the add-on through the Manipulate() or Convert() functions. The capabilities are added as name and type code pairs to the ioCapability message. This can be used by an application to check if an add-on supports a certain io extension.

The application interface

Here is a list of the functions that an application can use in the image manipulation library.

  /* Get the current version of the library and the minimum
     version with which it is still compatible */
  const char *
  Image_Version(
      int32 *curVersion,             /* will receive the current version */
      int32 *minVersion);            /* will receive the minimum version */

  /* Initialize the library before usage */
  status_t
  Image_Init(
      const char *loadPath);         /* NULL for the default */

  /* Shutdown the library after usage */
  status_t
  Image_Shutdown();

  /* Get all image manipulators that support a given source bitmap
     and io extension */
  status_t
  Image_GetManipulators(
      BitmapAccessor *sourceBitmap,  /* NULL to get all manipulators */
      BMessage *ioExtension,         /* can be NULL */
      image_addon_id **outList,      /* call delete[] on it when done */
      int32 *outCount);              /* will receive amount in list */

  /* Get all image converters that support a given source bitmap
     and io extension */
  status_t
  Image_GetConverters(
      BitmapAccessor *sourceBitmap,  /* NULL to get all converters */
      BMessage *ioExtension,         /* can be NULL */
      image_addon_id **outList,      /* call delete[] on it when done */
      int32 *outCount);              /* will receive amount in list */

  /* Get info on an image manipulator or image converter add-on */
  status_t
  Image_GetAddonInfo(
      image_addon_id imageAddon,
      const char **addonName,        /* will receive pointer to the name */
      const char **addonInfo,        /* will receive pointer to the info */
      const char **addonCategory     /* will receive pointer to the category */
      int32 *addonVersion);          /* will receive the version */

  /* Let an add-on manipulate a bitmap */
  status_t
  Image_Manipulate(
      image_addon_id imageManipulator,
      BitmapAccessor *sourceBitmap,
      BMessage *ioExtension,         /* can be NULL */
      bool checkOnly = false);

  /* Let an add-on convert a bitmap to another bitmap */
  status_t
  Image_Convert(
      image_addon_id imageConverter,
      BitmapAccessor *sourceBitmap,
      BitmapAccessor *destBitmap,    /* will be called CreateBitmap() on */
      BMessage *ioExtension,         /* can be NULL */
      bool checkOnly = false);

  /* Let an add-on make a BView that allows the user to configure it */
  status_t
  Image_MakeConfigurationView(
      image_addon_id imageAddon,
      BMessage *ioExtension,         /* can be NULL */
      BView **configView);           /* will receive pointer to the new BView */

  /* Get configuration and capabilities from an add-on */
  status_t
  Image_GetConfigurationMessage(
      image_addon_id imageAddon,
      BMessage *ioExtension,         /* message to add config info to */
      BMessage *ioCapability);       /* message to add capability info to */

  /* Create a new BBitmapAccessor object; mimics the constructor */
  BBitmapAccessor *
  Image_CreateBBitmapAccessor(
      BBitmap *bitmap = NULL,
      const BRect *section = NULL);

To use the library in your own applications you have two options:

Normal linkage

Include the file 'ImageManip.h', and link directly against the library. Just add the file 'libimagemanip.so' to your project by dropping it on the BeIDE.

Weak linkage

This allows applications to run even if libimagemanip.so isn't installed. Add the file 'ImportImageManip.cpp' to your application's project. Be careful to define the symbol _IMPEXP_IMAGEMANIP to nothing before including any of the library's header files. With weak linkage, you have to use the Image_CreateBBitmapAccessor() function to create new BBitmapAccessor objects.

Standard io extensions

Name	Type	Description
"color_space"	B_INT32_TYPE	If possible, create the new bitmap with this color space when you call CreateBitmap().
"selection_rect"	B_RECT_TYPE	Selection rectangle; the pixels that make up the edge of the rectangle are considered included in the rectangle.
"selection_map"	B_POINTER_TYPE	Selection bitmap; the pointer is to a BitmapAccessor object which defines an "alpha" channel to determine selected-ness.
"use_alpha"	B_BOOL_TYPE	Use the alpha channel for determining selected-ness (for B_RGBA32 and friends).
"progress_invoker"	B_POINTER_TYPE	Pointer to a BInvoker for sending progress messages with the amount of completion added. E.g. AddFloat("completion", 0.5) for 50%.

History

Release 1.0.0 (Nov 18th 1999)

• Upped the version number to 1.0.0, because Gobe Productive is going to use the image manipulation library.
• BitmapAccessor::BytesPerPixel() now uses the OS function get_pixel_size_for().
• Thanks to Scott Lindsey for compiling the PowerPC versions, since my BeBox is broken.

Release 0.6.1 (Jan 4th, 1999)

• Ported to BeOS R4.
• Included GammaCorrect image manipulator add-on.

Release 0.6.0 (Aug 23th, 1998)

• In, out, make your mind up! I moved the implementation of the bitmap accessor classes back into the library. You should remove the 'BitmapAccessor.cpp' file from your application's project again. Suggested by Jon Watte.
• Added an extra exported function for creating a BBitmapAccessor object. This is needed when using weak linkage with the library.
• Added a standard io extension for progress indication. Suggested by Scott Lindsey.
• Removed the readOnly argument from BitmapAccessor::AccessBits(). Instead, you can now call the new BitsNotChanged() function when you are finished with the bits, and didn't change them. This is better then having to know beforehand that you aren't going to change anything. Suggested by Jon Watte.
• Added a section BRect pointer argument to the constructor of BBitmapAccessor. If specified, it will limit access to the given area. I.e. Bounds() will return a smaller area. Suggested by Jon Watte.
• Fixed problems in BBitmapAccessor::AccessBits() with fractional BRect values.
• Added an example application (ImageManipExample) with source code to the distribution.
• Now scans the library path when loading the library as an add-on. The code for this was snipped from Jon Watte's libprefs. Suggested by Jon Watte.

Release 0.5.0 (Aug 9th, 1998)

• Wrote code to import the functions from the library as an add-on. This allows applications to run even if libimagemanip.so isn't installed. Suggested by Jon Watte.
• Removed bitmap accessor implementations from the library. You will have to add the file 'BitmapAccessor.cpp' to your application's project.
• Removed const restrictions in the BitmapAccessor abstract base class.
• Add-ons may export a C string with the category which they fall into. Examples of such categories would be Color, Effect, Filter, Composite, etc. Suggested by Trent Trautman and Scott Lindsey.
• Add-ons can be run in check-only mode from the library's API. Suggested by Scott Lindsey.

Release 0.4.0 (Jul 13th, 1998)

• Added some extra virtuals to the proxy class for possible future expansion. Suggested by Jon Watte.
• BBitmapAccessor is implemented in the library instead of the header file, and has a SetInvokers() function for setting invokers that send messages when the bitmap is created and when it is updated.
• Added more color spaces to the BytesPerPixel() function.
• Rewrote the example add-ons so that they only access one row of pixels at a time.
• Added some standard io extensions to the documentation. Suggested by Jon Watte.
• The 'MakeGray' add-on now understands the 'selection_rect' io extension.

Release 0.3.0 (Jul 6th, 1998)

• Introduced a proxy class for accessing bitmaps. Suggested by Jon Watte.
• Ditched the talkback invokers. Not needed any more because of the proxy class.
• Added ioCapability argument to GetConfigMessage(). This allows an application to check if an add-on supports a certain io extension. Suggested by Jon Watte.

Release 0.2.0 (Jun 22nd, 1998)

• First public (alpha) release.

Installation

To be able to use the library, you should copy the file 'libimagemanip.so' to the folder 'boot/home/config/lib'. You also need some add-ons in the folder 'boot/home/config/add-ons/ImageManip'.

Public domain

The image manipulation library was written by Edmund Vermeulen, based on the original code of the datatypes library written by Jon Watte.

The library, its example application, and the example add-ons are public domain. There are no restrictions on distribution or usage.

This should ensure the future of the library, even if for some reason I should decide to stop maintaining it. In the mean time I would like to receive any comments or suggestions that you might have. Please write to me at edmundv@xs4all.nl.