skia2/include/core/SkFontHost.h

/*
 * Copyright (C) 2006 The Android Open Source Project
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

#ifndef SkFontHost_DEFINED
#define SkFontHost_DEFINED

#include "SkScalerContext.h"
#include "SkTypeface.h"

class SkDescriptor;
class SkStream;
class SkWStream;

/** \class SkFontHost

    This class is ported to each environment. It is responsible for bridging
    the gap between the (sort of) abstract class SkTypeface and the
    platform-specific implementation that provides access to font files.
 
    One basic task is for each create (subclass of) SkTypeface, the FontHost is
    resonsible for assigning a uniqueID. The ID should be unique for the
    underlying font file/data, not unique per typeface instance. Thus it is
    possible/common to request a typeface for the same font more than once
    (e.g. asking for the same font by name several times). The FontHost may
    return seperate typeface instances in that case, or it may choose to use a
    cache and return the same instance (but calling typeface->ref(), since the
    caller is always responsible for calling unref() on each instance that is
    returned). Either way, the fontID for those instance(s) will be the same.
    In addition, the fontID should never be set to 0. That value is used as a
    sentinel to indicate no-font-id.
 
    The major aspects are:
    1) Given either a name/style, return a subclass of SkTypeface that
        references the closest matching font available on the host system.
    2) Given the data for a font (either in a stream or a file name), return
        a typeface that allows access to that data.
    3) Each typeface instance carries a 32bit ID for its corresponding font.
        SkFontHost turns that ID into a stream to access the font's data.
    4) Given a font ID, return a subclass of SkScalerContext, which connects a
        font scaler (e.g. freetype or other) to the font's data.
    5) Utilites to manage the font cache (budgeting) and gamma correction
*/
class SkFontHost {
public:
    /** Return a new, closest matching typeface given either an existing family
        (specified by a typeface in that family) or by a familyName, and a
        requested style.
        1) If familyFace is null, use famillyName.
        2) If famillyName is null, use familyFace.
        3) If both are null, return the default font that best matches style
     */
    static SkTypeface* CreateTypeface(const SkTypeface* familyFace,
                                      const char famillyName[],
                                      SkTypeface::Style style);

    /** Return a new typeface given the data buffer. If the data does not
        represent a valid font, returns null.
     
        If a typeface instance is returned, the caller is responsible for
        calling unref() on the typeface when they are finished with it.
     
        The returned typeface may or may not have called ref() on the stream
        parameter. If the typeface has not called ref(), then it may have made
        a copy of the releveant data. In either case, the caller is still
        responsible for its refcnt ownership of the stream. 
     */
    static SkTypeface* CreateTypefaceFromStream(SkStream*);
    
    /** Return a new typeface from the specified file path. If the file does not
        represent a valid font, this returns null. If a typeface is returned,
        the caller is responsible for calling unref() when it is no longer used.
     */
    static SkTypeface* CreateTypefaceFromFile(const char path[]);
    
    ///////////////////////////////////////////////////////////////////////////
    
    /** Returns true if the specified unique ID matches an existing font.
        Returning false is similar to calling OpenStream with an invalid ID,
        which will return NULL in that case.
    */
    static bool ValidFontID(uint32_t uniqueID);
    
    /** Return a new stream to read the font data, or null if the uniqueID does
        not match an existing typeface. .The caller must call stream->unref()
        when it is finished reading the data.
    */
    static SkStream* OpenStream(uint32_t uniqueID);

    ///////////////////////////////////////////////////////////////////////////

    /** Write a unique identifier to the stream, so that the same typeface can
        be retrieved with Deserialize().
    */
    static void Serialize(const SkTypeface*, SkWStream*);

    /** Given a stream created by Serialize(), return a new typeface (like
        CreateTypeface) or return NULL if no match is found.
     */
    static SkTypeface* Deserialize(SkStream*);

    ///////////////////////////////////////////////////////////////////////////
    
    /** Return a subclass of SkScalarContext
    */
    static SkScalerContext* CreateScalerContext(const SkDescriptor* desc);

    /** Return a scalercontext using the "fallback" font. If there is no
        designated fallback, return null.
    */
    static SkScalerContext* CreateFallbackScalerContext(
                                                const SkScalerContext::Rec&);

    ///////////////////////////////////////////////////////////////////////////
    
    /** Return the number of bytes (approx) that should be purged from the font
        cache. The input parameter is the cache's estimate of how much as been
        allocated by the cache so far.
        To purge (basically) everything, return the input parameter.
        To purge nothing, return 0
    */
    static size_t ShouldPurgeFontCache(size_t sizeAllocatedSoFar);

    /** Return SkScalerContext gamma flag, or 0, based on the paint that will be
        used to draw something with antialiasing.
    */
    static int ComputeGammaFlag(const SkPaint& paint);

    /** Return NULL or a pointer to 256 bytes for the black (table[0]) and
        white (table[1]) gamma tables.
    */
    static void GetGammaTables(const uint8_t* tables[2]);
};

#endif