WIP -- SkFont

include/core/SkFont.h

+/*
+ * Copyright 2014 Google Inc.
+ *
+ * Use of this source code is governed by a BSD-style license that can be
+ * found in the LICENSE file.
+ */
+
+#include "SkRefCnt.h"
+#include "SkScalar.h"
+
+class SkPaint;
+class SkTypeface;
+
+enum SkTextEncoding {
+    kUTF8_SkTextEncoding,
+    kUTF16_SkTextEncoding,
+    kUTF32_SkTextEncoding,
+    kGlyphID_SkTextEncoding,
+};
+
+/*
+ 1. The Hinting enum in SkPaint is gone entirely, absorbed into SkFont's flags.
+ 
+ 2. SkPaint Flags look like this today
+ 
+ enum Flags {
+     kAntiAlias_Flag       = 0x01,   //!< mask to enable antialiasing
+     kDither_Flag          = 0x04,   //!< mask to enable dithering
+     kUnderlineText_Flag   = 0x08,   //!< mask to enable underline text
+     kStrikeThruText_Flag  = 0x10,   //!< mask to enable strike-thru text
+     kFakeBoldText_Flag    = 0x20,   //!< mask to enable fake-bold text
+     kLinearText_Flag      = 0x40,   //!< mask to enable linear-text
+     kSubpixelText_Flag    = 0x80,   //!< mask to enable subpixel text positioning
+     kDevKernText_Flag     = 0x100,  //!< mask to enable device kerning text
+     kLCDRenderText_Flag   = 0x200,  //!< mask to enable subpixel glyph renderering
+     kEmbeddedBitmapText_Flag = 0x400, //!< mask to enable embedded bitmap strikes
+     kAutoHinting_Flag     = 0x800,  //!< mask to force Freetype's autohinter
+     kVerticalText_Flag    = 0x1000,
+     kGenA8FromLCD_Flag    = 0x2000, // hack for GDI -- do not use if you can help it
+ };
+
+ SkFont would absorb these:
+ 
+     kFakeBoldText_Flag    = 0x20,   //!< mask to enable fake-bold text
+     kLinearText_Flag      = 0x40,   //!< mask to enable linear-text
+     kSubpixelText_Flag    = 0x80,   //!< mask to enable subpixel text positioning
+     kDevKernText_Flag     = 0x100,  //!< mask to enable device kerning text
+     kLCDRenderText_Flag   = 0x200,  //!< mask to enable subpixel glyph renderering
+     kEmbeddedBitmapText_Flag = 0x400, //!< mask to enable embedded bitmap strikes
+     kAutoHinting_Flag     = 0x800,  //!< mask to force Freetype's autohinter
+     kVerticalText_Flag    = 0x1000,
+     kGenA8FromLCD_Flag    = 0x2000, // hack for GDI -- do not use if you can help it
+
+ leaving these still in paint
+
+     kAntiAlias_Flag       = 0x01,   //!< mask to enable antialiasing
+     kDither_Flag          = 0x04,   //!< mask to enable dithering
+     kUnderlineText_Flag   = 0x08,   //!< mask to enable underline text
+     kStrikeThruText_Flag  = 0x10,   //!< mask to enable strike-thru text
+
+ 3. Antialiasing
+ 
+    SkFont has a mask-type: BW, AA, LCD
+    SkPaint has antialias boolean
+ 
+    What to do if the font's mask-type disagrees with the paint?
+
+ */
+
+class SkFont : public SkRefCnt {
+public:
+    enum Flags {
+        /**
+         *  Use the system's automatic hinting mechanism to hint the typeface.
+         *  If both bytecode and auto hints are specified, attempt to use the bytecodes first.
+         *  If that fails (e.g. there are no codes), then attempt to autohint.
+         */
+        kEnableAutoHints_Flag       = 1 << 0,
+
+        /**
+         *  If the typeface contains explicit bytecodes for hinting, use them.
+         *  If both bytecode and auto hints are specified, attempt to use the bytecodes first;
+         *  if that fails (e.g. there are no codes), then attempt to autohint.
+         */
+        kEnableByteCodeHints_Flag   = 1 << 1,
+
+        /**
+         *  Use rounded metric values (e.g. advance).
+         *  If either auto or bytecode hinting was used, apply those results to the metrics of the
+         *  glyphs as well. If no hinting was applied, the metrics will just be rounded to the
+         *  nearest integer.
+         *
+         *  This applies to calls that return metrics (e.g. measureText) and to drawing the glyphs
+         *  (see SkCanvas drawText and drawPosText).
+         */
+        kUseNonlinearMetrics_Flag   = 1 << 2,
+
+        kVertical_Flag              = 1 << 3,
+        kEmbeddedBitmaps_Flag       = 1 << 4,

[bungeman-skia, 2014/05/02 19:29:43]

I was just working on this with relation to DirectWrite, and wanted to point out
that the kEmbeddedBitmaps_Flag is actually a hinting flag. In a certain sense,
it's 'hinting' taken to an extreme. As a result, I propose that this flag be
renamed kEnableBitmapHints_Flag (If the typeface contains embedded bitmaps, use
them. If bitmap, bytecode, and auto hints are specified, attempt to use the
bitmaps first.) Part of the reason for this is to allow the use of embedded
bitmaps, but allow the user to specify whether they want the linear metrics or
to use the bitmap metrics.

Unfortunately, I can also see a user wanting to use linear metrics for bytecode
and auto hinting, but use the bitmap advances when using bitmaps. This is, for
example, what FireFox does. However, we were trying to avoid having
kEnableXXXHints_Flag/kApplyXXXHintsToMetrics_Flag combinations.

+        kGenA8FromLCD_Flag          = 1 << 5,
+        kEmbolden_Flag              = 1 << 6,
+        kDevKern_Flag               = 1 << 7,   // ifdef ANDROID ?
+    };
+
+    enum MaskType {
+        kBW_MaskType,
+        kA8_MaskType,
+        kLCD_MaskType,
+    };
+
+    static SkFont* Create(SkTypeface*, SkScalar size, MaskType, uint32_t flags);
+    static SkFont* Create(SkTypeface*, SkScalar size, SkScalar scaleX, SkScalar skewX,
+                          MaskType, uint32_t flags);
+
+    /**
+     *  Return a font with the same attributes of this font, but with the specified size.
+     *  If size is not supported (e.g. <= 0 or non-finite) NULL will be returned.
+     */
+    SkFont* cloneWithSize(SkScalar size) const;
+
+    SkTypeface* getTypeface() const { return fTypeface; }
+    SkScalar    getSize() const { return fSize; }
+    SkScalar    getScaleX() const { return fScaleX; }
+    SkScalar    getSkewX() const { return fSkewX; }
+    uint32_t    getFlags() const { return fFlags; }
+    MaskType    getMaskType() const { return (MaskType)fMaskType; }
+
+    int textToGlyphs(const void* text, size_t byteLength, SkTextEncoding,
+                     uint16_t glyphs[], int maxGlyphCount) const;
+
+    SkScalar measureText(const void* text, size_t byteLength, SkTextEncoding) const;
+
+    static SkFont* Testing_CreateFromPaint(const SkPaint&);
+
+private:
+    enum {
+        kAllFlags = 0xFF,
+    };
+    
+    SkFont(SkTypeface*, SkScalar size, SkScalar scaleX, SkScalar skewX, MaskType, uint32_t flags);
+    virtual ~SkFont();
+
+    SkTypeface* fTypeface;
+    SkScalar    fSize;
+    SkScalar    fScaleX;
+    SkScalar    fSkewX;
+    uint16_t    fFlags;
+    uint8_t     fMaskType;
+    uint8_t     fPad;
+};
+