gecko-dev/gfx/public/nsIFontMetrics.h

/* -*- Mode: C++; tab-width: 2; indent-tabs-mode: nil; c-basic-offset: 2 -*-
 *
 * The contents of this file are subject to the Netscape Public License
 * Version 1.0 (the "NPL"); you may not use this file except in
 * compliance with the NPL.  You may obtain a copy of the NPL at
 * http://www.mozilla.org/NPL/
 *
 * Software distributed under the NPL is distributed on an "AS IS" basis,
 * WITHOUT WARRANTY OF ANY KIND, either express or implied. See the NPL
 * for the specific language governing rights and limitations under the
 * NPL.
 *
 * The Initial Developer of this code under the NPL is Netscape
 * Communications Corporation.  Portions created by Netscape are
 * Copyright (C) 1998 Netscape Communications Corporation.  All Rights
 * Reserved.
 */

#ifndef nsIFontMetrics_h___
#define nsIFontMetrics_h___

#include "nsISupports.h"
#include "nsCoord.h"

struct nsFont;
class nsString;
class nsIDeviceContext;

// IID for the nsIFontMetrics interface
#define NS_IFONT_METRICS_IID   \
{ 0xc74cb770, 0xa33e, 0x11d1, \
{ 0xa8, 0x24, 0x00, 0x40, 0x95, 0x9a, 0x28, 0xc9 } }

//----------------------------------------------------------------------

/**
 * A native font handle
 */
typedef void* nsFontHandle;

/**
 * Font metrics interface
 */
class nsIFontMetrics : public nsISupports
{
  // XXX what about encoding, where do we put that? MMP

public:
  static const nsIID& GetIID() { static nsIID iid = NS_IFONT_METRICS_IID; return iid; }

  /**
   * Initialize the font metrics. Call this after creating the font metrics.
   * Font metrics you get from the font cache do NOT need to be initialized
   *
   * @see nsIDeviceContext#GetMetricsFor()
   */
  NS_IMETHOD  Init(const nsFont& aFont, nsIDeviceContext *aContext) = 0;

  /**
   * Destroy this font metrics. This breaks the association between
   * the font metrics and the device context.
   */
  NS_IMETHOD  Destroy() = 0;

  /**
   * Return the font's xheight property, scaled into app-units.
   */
  NS_IMETHOD  GetXHeight(nscoord& aResult) = 0;

  /**
   * Return the font's superscript offset (the distance from the
   * baseline to where a superscript's baseline should be placed). The
   * value returned will be a positive value.
   */
  NS_IMETHOD  GetSuperscriptOffset(nscoord& aResult) = 0;

  /**
   * Return the font's subscript offset (the distance from the
   * baseline to where a subscript's baseline should be placed). The
   * value returned will be a positive value.
   */
  NS_IMETHOD  GetSubscriptOffset(nscoord& aResult) = 0;

  /**
   * Return the font's strikeout offset (the distance from the 
   * baseline to where a strikeout should be placed) and size
   * Positive values are above the baseline, negative below.
   */
  NS_IMETHOD  GetStrikeout(nscoord& aOffset, nscoord& aSize) = 0;

  /**
   * Return the font's underline offset (the distance from the 
   * baseline to where a underline should be placed) and size.
   * Positive values are above the baseline, negative below.
   */
  NS_IMETHOD  GetUnderline(nscoord& aOffset, nscoord& aSize) = 0;

  /**
   * Returns the height (in app units) of the font. This is ascent plus descent
   * plus any internal leading
   */
  NS_IMETHOD  GetHeight(nscoord &aHeight) = 0;

  /**
   * Returns the amount of internal leading (in app units) for the font. This
   * is computed as the "height  - (ascent + descent)"
   */
  NS_IMETHOD  GetLeading(nscoord &aLeading) = 0;

  /**
   * Returns, in app units, the maximum distance characters in this font extend
   * above the base line.
   */
  NS_IMETHOD  GetMaxAscent(nscoord &aAscent) = 0;

  /**
   * Returns, in app units, the maximum distance characters in this font extend
   * below the base line.
   */
  NS_IMETHOD  GetMaxDescent(nscoord &aDescent) = 0;

  /**
   * Returns, in app units, the maximum character advance for the font
   */
  NS_IMETHOD  GetMaxAdvance(nscoord &aAdvance) = 0;

  /**
   * Returns the font associated with these metrics
   */
  NS_IMETHOD  GetFont(const nsFont *&aFont) = 0;

  /**
   * Returns the font handle associated with these metrics
   */
  NS_IMETHOD  GetFontHandle(nsFontHandle &aHandle) = 0;
};

#endif /* nsIFontMetrics_h___ */