
/*
 * @(#)LayoutEngine.h	1.4 00/03/15
 *
 * (C) Copyright IBM Corp. 1998, 1999, 2000 - All Rights Reserved
 *
 */

#ifndef __LAYOUTENGINE_H
#define __LAYOUTENGINE_H

#include "LETypes.h"
#include "LEFontInstance.h"
#include "LEGlyphFilter.h"

#include "unicode/utypes.h"

#include <string.h>

#define ARRAY_COPY(dst, src, count) memcpy(dst, src, (count) * sizeof (src)[0])

/**
 * This is a virtual base class used to do complex text layout. The text must all
 * be in a single font, script, and language. An instance of a LayoutEngine can be
 * created by calling the layoutEngineFactory method. Fonts are identified by
 * instances of the LEFontInstance class. Script and language codes are identified
 * by integer codes, which are defined in ScriptAndLanuageTags.h.
 *
 * The input to the layout process is an array of characters in logical order,
 * and a starting X, Y position for the text. The output is an array of glyph indices,
 * an array of character indices for the glyphs, and an array of glyph positions.
 * These arrays are protected members of LayoutEngine which can be retreived by a
 * public method. The reset method can be called to free these arrays so that the
 * LayoutEngine can be reused.
 *
 * The layout process is done in three steps. There is a protected virtual method
 * for each step. These methods have a default implementation which only does
 * character to glyph mapping and default positioning using the glyph's advance
 * widths. Subclasses can override these methods for more advanced layout.
 * There is a public method which invokes the steps in the correct order.
 * 
 * The steps are:
 *
 * 1) Glyph processing - character to glyph mapping and any other glyph processing
 *    such as ligature substitution and contextual forms.
 *
 * 2) Glyph positioning - position the glyphs based on their advance widths.
 *
 * 3) Glyph position adjustments - adjustment of glyph positions for kerning,
 *    accent placement, etc.
 *
 * NOTE: in all methods below, output parameters are references to pointers so
 * the method can allocate and free the storage as needed. All storage allocated
 * in this way is owned by the object which created it, and will be freed when it
 * is no longer needed, or when the object's destructor is invoked.
 *
 * @see LEFontInstance
 * @see ScriptAndLanguageTags.h
 */
class U_LAYOUT_API LayoutEngine
{
protected:
	/**
	 * The number of glyphs in the output
	 */
    le_int32 fGlyphCount;

	/**
	 * The output glyph array
	 */
    LEGlyphID *fGlyphs;

	/**
	 * The character index array. One entry for each output glyph, giving the index
	 * in the input character array of the character which corresponds to this glyph.
	 */
    le_int32 *fCharIndices;

	/**
	 * The glyph position array. There are two entries for each glyph giving the
	 * X and Y positions of the glyph. Thus, for glyph i, the X position is at index
	 * 2i, and the Y position is at index 2i + 1.
	 */
    float *fPositions;

	/**
	 * The font instance for the text font.
	 *
	 * @see LEFontInstance
	 */
    LEFontInstance *fFontInstance;

	/**
	 * The script code for the text
	 *
	 * @see ScriptAndLanguageTags.h for script codes.
	 */
    le_int32 fScriptCode;

	/**
	 * The langauge code for the text
	 *
	 * @see ScriptAndLanguageTags.h for language codes.
	 */
    le_int32 fLanguageCode;

	/**
	 * This constructs an instance for a given font, script and language. Subclass constructors
	 * must call this constructor.
	 *
	 * @param fontInstance - the font for the text
	 * @param scriptCode - the script for the text
	 * @param langaugeCode - the language for the text
	 *
	 * @see LEFontInstance
	 * @see ScriptAndLanguageTags.h
	 */
    LayoutEngine(LEFontInstance *fontInstance, le_int32 scriptCode, le_int32 languageCode);

    /**
	 * This overrides the default no argument constructor to make it
	 * difficult for clients to call it. Clients are expected to call
	 * layoutEngineFactory.
	 */
    LayoutEngine();

	/**
	 * This method does the glyph processing. It converts an array of characters
	 * into an array of glyph indices and character indices. The characters to be
	 * processed are passed in a surrounding context. The context is specified as
	 * a starting address and a maximum character count. An offset and a count are
	 * used to specify the characters to be processed.
	 *
	 * The default implementation of this method only does character to glyph mapping.
	 * Subclasses needing more elaborate glyph processing must override this method.
	 *
	 * Input parameters:
	 * @param chars - the character context
	 * @param offset - the offset of the first character to process
	 * @param count - the number of characters to process
	 * @param max - the number of characters in the context.
	 * @param rightToLeft - true if the text is in a right to left directional run
	 *
	 * Output parameters:
	 * @param glyphs - the glyph index array
	 * @param charIndices - the character index array
	 *
	 * @return the number of glyphs in the glyph index array
	 */
    virtual le_int32 computeGlyphs(const LEUnicode chars[], le_int32 offset, le_int32 count, le_int32 max, le_bool rightToLeft, LEGlyphID *&glyphs, le_int32 *&charIndices);

	/**
	 * This method does basic glyph positioning. The default implementation positions
	 * the glyphs based on their advance widths. This is sufficient for most uses. It
	 * is not expected that many subclasses will override this method.
	 *
	 * Input parameters:
	 * @param glyphs - the input glyph array
	 * @param glyphCount - the number of glyphs in the glyph array
	 * @param x - the starting X position
	 * @param y - the starting Y position
	 *
	 * Output parameters:
	 * @param positions - the output X and Y positions (two entries per glyph)
	 */
    virtual void positionGlyphs(const LEGlyphID glyphs[], le_int32 glyphCount, float x, float y, float *&positions);

	/**
	 * This method does positioning adjustments like accent positioning and
	 * kerning. The default implementation does nothing. Subclasses needing
	 * position adjustments must override this method.
	 *
	 * Note that this method has both characters and glyphs as input so that
	 * it can use the character codes to determine glyph types if that information
	 * isn't directly available. (e.g. Some Arabic OpenType fonts don't have a GDEF
	 * table)
	 *
	 * @param chars - the input character context
	 * @param offset - the offset of the first character to process
	 * @param count - the number of characters to process
	 * @param reverse - true if the glyphs in the glyph array have been reordered
	 * @param glyphs - the input glyph array
	 * @param glyphCount - the number of glyphs
	 * @param positions - the position array, will be updated as needed
	 *
	 * Note: the positions are passed as a plain array because this method should
	 * not need to reallocate them.
	 */
    virtual void adjustGlyphPositions(const LEUnicode chars[], le_int32 offset, le_int32 count, le_bool reverse, LEGlyphID glyphs[], le_int32 glyphCount, float positions[])
    {
        // default is no adjustments
    };

	/**
	 * This method gets a table from the font associated with
	 * the text. The default implementation gets the table from
	 * the font instance. Subclasses which need to get the tables
	 * some other way must override this method.
	 * 
	 * @param tableTag - the four byte table tag.
	 *
	 * @return the address of the table.
	 */
    virtual const void *getFontTable(LETag tableTag)
    {
        return fFontInstance->getFontTable(tableTag);
    };

	/**
	 * This method does character to glyph mapping. The default implementation
	 * uses the font instance to do the mapping. It will allocate the glyph and
	 * character index arrays if they're not already allocated. If it allocates the
	 * character index array, it will fill it it.
	 *
	 * This method supports right to left
	 * text with the ability to store the glyphs in reverse order, and by supporting
	 * character mirroring, which will replace a character which has a left and right
	 * form, such as parens, with the opposite form before mapping it to a glyph index.
	 *
	 * Input parameters:
	 * @param chars - the input character context
	 * @param offset - the offset of the first character to be mapped
	 * @param count - the number of characters to be mapped
	 * @param reverse - if true, the output will be in reverse order
	 * @param mirror - if true, do character mirroring
	 *
	 * Output parameters:
	 * @param glyphs - the glyph array
	 * @param charIndices - the character index array
	 *
	 * @see LEFontInstance
	 */
    virtual void mapCharsToGlyphs(const LEUnicode chars[], le_int32 offset, le_int32 count, le_bool reverse, le_bool mirror, LEGlyphID *&glyphs, le_int32 *&charIndices);

	/**
	 * This is a convenience method that forces the advance width of mark
	 * glyphs to be zero, which is required for proper selection and highlighting.
	 * 
	 * @param glyphs - the glyph array
	 * @param glyphCount - the number of glyphs
	 * @param reverse - true if the glyph array has been reordered
	 * @param markFilter - used to identify mark glyphs
	 * @param positions - the glyph position array - updated as required
	 *
	 * @see LEGlyphFilter
	 */
    static void adjustMarkGlyphs(const LEGlyphID glyphs[], le_int32 glyphCount, le_bool reverse, LEGlyphFilter *markFilter, float positions[]);

public:
	/**
	 * The destructor. It will free any storage allocated for the
	 * glyph, character index and position arrays by calling the reset
	 * method. It is declared virtual so that it will be invoked by the
	 * subclass destructors.
	 */
    virtual ~LayoutEngine();

	/**
	 * This method will invoke the layout steps in their correct order by calling
	 * the computeGlyphs, positionGlyphs and adjustGlyphPosition methods.. It will
	 * compute the glyph, character index and position arrays.
	 *
	 * @param chars - the input character context
	 * @param offset - the offset of the first character to process
	 * @param count - the number of characters to process
	 * @param max - the number of characters in the input context
	 * @param rightToLeft - true if the characers are in a right to left directional run
	 * @param x - the initial X position
	 * @param y - the initial Y position
	 *
	 * @return the number of glyphs in the glyph array
	 *
	 * Note; the glyph, character index and position array can be accessed
	 * using the getter method below.
	 */
    le_int32 layoutChars(const LEUnicode chars[], le_int32 offset, le_int32 count, le_int32 max, le_bool rightToLeft, float x, float y);

	/**
	 * This method copies the glyph array into a caller supplied array.
	 * The caller must ensure that the array is large enough to hold all
	 * the glyphs.
	 *
	 * @param glyphs - the destiniation glyph array
	 */
    void getGlyphs(LEGlyphID glyphs[])
    {
        ARRAY_COPY(glyphs, fGlyphs, fGlyphCount);
    };

	/**
	 * This method copies the glyph array into a caller supplied array,
	 * ORing in extra bits. (This functionality is needed by the JDK,
	 * which uses 32 bits pre glyph idex, with the high 16 bits encoding
	 * the composite font slot number)
	 *
	 * @param glyphs - the destination (32 bit) glyph array
	 * @param extraBits - this value will be ORed with each glyph index
	 */
    void getGlyphs(le_uint32 glyphs[], le_uint32 extraBits);

	/**
	 * This method copies the character index array into a caller supplied array.
	 * The caller must ensure that the array is large enough to hold all
	 * the character indices.
	 *
	 * @param charIndices - the destiniation character index array
	 */
    void getCharIndices(le_int32 charIndices[])
    {
        ARRAY_COPY(charIndices, fCharIndices, fGlyphCount);
    };

	/**
	 * This method copies the character index array into a caller supplied array.
	 * The caller must ensure that the array is large enough to hold all
	 * the character indices.
	 *
	 * @param charIndices - the destiniation character index array
	 * @param indexBase - an offset which will be added to each index
	 */
    void getCharIndices(le_int32 charIndices[], le_int32 indexBase);

	/**
	 * This method copies the position array into a caller supplied array.
	 * The caller must ensure that the array is large enough to hold all
	 * the positions.
	 *
	 * @param glyphs - the destiniation position array
	 */
    void getGlyphPositions(float positions[])
    {
        ARRAY_COPY(positions, fPositions, fGlyphCount * 2 + 2);
    };

	/**
	 * This method returns the x position of the glyph at the
	 * given index.
	 *
	 * @param glyphIndex - the index of the glyph
	 *
	 * @return the glyph's x position
	 */
    float getGlyphXPosition(le_int32 glyphIndex)
    {
        return fPositions[glyphIndex * 2];
    };

	/**
	 * This method frees the glyph, character index and position arrays
	 * so that the LayoutEngine can be reused to layout a different
	 * characer array. (This method is also called by the destructor)
	 */
    virtual void reset();
    
	/**
	 * This method returns a LayoutEngine capable of laying out text
	 * in the given font, script and langauge. Note that the LayoutEngine
	 * returned may be a subclass of LayoutEngine.
	 *
	 * @param fontInstance - the font of the text
	 * @param scriptCode - the script of the text
	 * @param langaugeCode - the language of the text
	 *
	 * @see LEFontInstance
	 */
    static LayoutEngine *layoutEngineFactory(LEFontInstance *fontInstance, le_int32 scriptCode, le_int32 languageCode);
    
};

#endif