path: root/gfx/font.h

// Copyright (c) 2006-2008 The Chromium Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

#ifndef GFX_FONT_H_
#define GFX_FONT_H_
#pragma once

#include "build/build_config.h"

#include <string>

#if defined(OS_WIN)
typedef struct HFONT__* HFONT;
#elif !defined(OS_MACOSX)
#include "third_party/skia/include/core/SkRefCnt.h"
class SkPaint;
class SkTypeface;
#endif

#if defined(OS_WIN)
typedef struct HFONT__* NativeFont;
#elif defined(OS_MACOSX)
#ifdef __OBJC__
@class NSFont;
#else
class NSFont;
#endif
typedef NSFont* NativeFont;
#else
typedef struct _PangoFontDescription PangoFontDescription;
class SkTypeface;
typedef SkTypeface* NativeFont;
#endif

#include "base/basictypes.h"
#include "base/ref_counted.h"
#include "base/scoped_ptr.h"

namespace gfx {

// Font provides a wrapper around an underlying font. Copy and assignment
// operators are explicitly allowed, and cheap.
class Font {
 public:
  // The following constants indicate the font style.
  enum {
    NORMAL = 0,
    BOLD = 1,
    ITALIC = 2,
    UNDERLINED = 4,
  };

  // Creates a Font given font name (e.g. arial), font size (e.g. 12).
  // Skia actually expects a family name and not a font name.
  static Font CreateFont(const std::wstring& font_name, int font_size);

  ~Font() { }

  // Returns a new Font derived from the existing font.
  // size_deta is the size to add to the current font. For example, a value
  // of 5 results in a font 5 units bigger than this font.
  Font DeriveFont(int size_delta) const {
    return DeriveFont(size_delta, style());
  }

  // Returns a new Font derived from the existing font.
  // size_delta is the size to add to the current font. See the single
  // argument version of this method for an example.
  // The style parameter specifies the new style for the font, and is a
  // bitmask of the values: BOLD, ITALIC and UNDERLINED.
  Font DeriveFont(int size_delta, int style) const;

  // Returns the number of vertical pixels needed to display characters from
  // the specified font.  This may include some leading, i.e. height may be
  // greater than just ascent + descent.  Specifically, the Windows and Mac
  // implementations include leading and the Linux one does not.  This may
  // need to be revisited in the future.
  int height() const;

  // Returns the baseline, or ascent, of the font.
  int baseline() const;

  // Returns the average character width for the font.
  int ave_char_width() const;

  // Returns the number of horizontal pixels needed to display the specified
  // string.
  int GetStringWidth(const std::wstring& text) const;

  // Returns the expected number of horizontal pixels needed to display
  // the specified length of characters.
  // Call GetStringWidth() to retrieve the actual number.
  int GetExpectedTextWidth(int length) const;

  // Returns the style of the font.
  int style() const;

  // Font Name.
  // It is actually a font family name, because Skia expects a family name
  // and not a font name.
  const std::wstring& FontName() const;

  // Font Size.
  int FontSize();

  NativeFont nativeFont() const;

  // Creates a font with the default name and style.
  Font();

#if defined(OS_WIN)
  // Creates a Font from the specified HFONT. The supplied HFONT is effectively
  // copied.
  static Font CreateFont(HFONT hfont);

  // Returns the handle to the underlying HFONT. This is used by gfx::Canvas to
  // draw text.
  HFONT hfont() const { return font_ref_->hfont(); }

  // Dialog units to pixels conversion.
  // See http://support.microsoft.com/kb/145994 for details.
  int horizontal_dlus_to_pixels(int dlus) {
    return dlus * font_ref_->dlu_base_x() / 4;
  }
  int vertical_dlus_to_pixels(int dlus) {
    return dlus * font_ref_->height() / 8;
  }

  // Callback that returns the minimum height that should be used for
  // gfx::Fonts. Optional. If not specified, the minimum font size is 0.
  typedef int (*GetMinimumFontSizeCallback)();
  static GetMinimumFontSizeCallback get_minimum_font_size_callback;

  // Callback that adjusts a LOGFONT to meet suitability requirements of the
  // embedding application. Optional. If not specified, no adjustments are
  // performed other than clamping to a minimum font height if
  // |get_minimum_font_size_callback| is specified.
  typedef void (*AdjustFontCallback)(LOGFONT* lf);
  static AdjustFontCallback adjust_font_callback;

#elif !defined(OS_MACOSX)
  static Font CreateFont(PangoFontDescription* desc);
  // We need a copy constructor and assignment operator to deal with
  // the Skia reference counting.
  Font(const Font& other);
  Font& operator=(const Font& other);
  // Setup a Skia context to use the current typeface
  void PaintSetup(SkPaint* paint) const;

  // Converts |gfx_font| to a new pango font. Free the returned font with
  // pango_font_description_free().
  static PangoFontDescription* PangoFontFromGfxFont(const gfx::Font& gfx_font);

  // Position as an offset from the height of the drawn text, used to draw
  // an underline. This is a negative number, so the underline would be
  // drawn at y + height + underline_position;
  double underline_position() const;
  // The thickness to draw the underline.
  double underline_thickness() const;
#endif

 private:

#if defined(OS_WIN)
  // Chrome text drawing bottoms out in the Windows GDI functions that take an
  // HFONT (an opaque handle into Windows). To avoid lots of GDI object
  // allocation and destruction, Font indirectly refers to the HFONT by way of
  // an HFontRef. That is, every Font has an HFontRef, which has an HFONT.
  //
  // HFontRef is reference counted. Upon deletion, it deletes the HFONT.
  // By making HFontRef maintain the reference to the HFONT, multiple
  // HFontRefs can share the same HFONT, and Font can provide value semantics.
  class HFontRef : public base::RefCounted<HFontRef> {
   public:
    // This constructor takes control of the HFONT, and will delete it when
    // the HFontRef is deleted.
    HFontRef(HFONT hfont,
             int height,
             int baseline,
             int ave_char_width,
             int style,
             int dlu_base_x);

    // Accessors
    HFONT hfont() const { return hfont_; }
    int height() const { return height_; }
    int baseline() const { return baseline_; }
    int ave_char_width() const { return ave_char_width_; }
    int style() const { return style_; }
    int dlu_base_x() const { return dlu_base_x_; }
    const std::wstring& font_name() const { return font_name_; }

   private:
    friend class  base::RefCounted<HFontRef>;

    ~HFontRef();

    const HFONT hfont_;
    const int height_;
    const int baseline_;
    const int ave_char_width_;
    const int style_;
    // Constants used in converting dialog units to pixels.
    const int dlu_base_x_;
    std::wstring font_name_;

    DISALLOW_COPY_AND_ASSIGN(HFontRef);
  };

  // Returns the base font ref. This should ONLY be invoked on the
  // UI thread.
  static HFontRef* GetBaseFontRef();

  // Creates and returns a new HFONTRef from the specified HFONT.
  static HFontRef* CreateHFontRef(HFONT font);

  explicit Font(HFontRef* font_ref) : font_ref_(font_ref) { }

  // Reference to the base font all fonts are derived from.
  static HFontRef* base_font_ref_;

  // Indirect reference to the HFontRef, which references the underlying HFONT.
  scoped_refptr<HFontRef> font_ref_;
#elif !defined(OS_MACOSX)
  explicit Font(SkTypeface* typeface, const std::wstring& name,
                int size, int style);
  // Calculate and cache the font metrics.
  void calculateMetrics();
  // Make |this| a copy of |other|.
  void CopyFont(const Font& other);

  // The default font, used for the default constructor.
  static Font* default_font_;

  // Return the scale factor for fonts that account for DPI.
  static float GetPangoScaleFactor();

  // The average width of a character, initialized and cached if needed.
  double avg_width() const;

  // Potentially slow call to get pango metrics (avg width, underline info).
  void InitPangoMetrics();

  // These two both point to the same SkTypeface. We use the SkAutoUnref to
  // handle the reference counting, but without @typeface_ we would have to
  // cast the SkRefCnt from @typeface_helper_ every time.
  scoped_ptr<SkAutoUnref> typeface_helper_;
  SkTypeface *typeface_;

  // Additional information about the face
  // Skia actually expects a family name and not a font name.
  std::wstring font_family_;
  int font_size_;
  int style_;

  // Cached metrics, generated at construction
  int height_;
  int ascent_;

  // The pango metrics are much more expensive so we wait until we need them
  // to compute them.
  bool pango_metrics_inited_;
  double avg_width_;
  double underline_position_;
  double underline_thickness_;
#else  // OS_MACOSX
  explicit Font(const std::wstring& font_name, int font_size, int style);

  // Calculate and cache the font metrics.
  void calculateMetrics();

  std::wstring font_name_;
  int font_size_;
  int style_;

  // Cached metrics, generated at construction
  int height_;
  int ascent_;
  int avg_width_;
#endif

};

}  // namespace gfx

#endif  // GFX_FONT_H_