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88 lines
3.3 KiB
C++
88 lines
3.3 KiB
C++
/* -*- Mode: C++; tab-width: 20; indent-tabs-mode: nil; c-basic-offset: 4 -*- */
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/* This Source Code Form is subject to the terms of the Mozilla Public
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* License, v. 2.0. If a copy of the MPL was not distributed with this
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* file, You can obtain one at http://mozilla.org/MPL/2.0/. */
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#ifndef __nsBoundingMetrics_h
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#define __nsBoundingMetrics_h
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#include "nsCoord.h"
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#include <algorithm>
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/* Struct used for accurate measurements of a string, in order to
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* allow precise positioning when processing MathML. This is in its
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* own header file because some very-widely-included headers need it
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* but not the rest of nsFontMetrics, or vice versa.
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*/
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struct nsBoundingMetrics {
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///////////
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// Metrics that _exactly_ enclose the text:
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// The character coordinate system is the one used on X Windows:
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// 1. The origin is located at the intersection of the baseline
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// with the left of the character's cell.
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// 2. All horizontal bearings are oriented from left to right.
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// 2. All horizontal bearings are oriented from left to right.
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// 3. The ascent is oriented from bottom to top (being 0 at the orgin).
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// 4. The descent is oriented from top to bottom (being 0 at the origin).
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// Note that Win32/Mac/PostScript use a different convention for
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// the descent (all vertical measurements are oriented from bottom
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// to top on these palatforms). Make sure to flip the sign of the
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// descent on these platforms for cross-platform compatibility.
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// Any of the following member variables listed here can have
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// positive or negative value.
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nscoord leftBearing;
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/* The horizontal distance from the origin of the drawing
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operation to the left-most part of the drawn string. */
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nscoord rightBearing;
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/* The horizontal distance from the origin of the drawing
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operation to the right-most part of the drawn string.
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The _exact_ width of the string is therefore:
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rightBearing - leftBearing */
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nscoord ascent;
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/* The vertical distance from the origin of the drawing
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operation to the top-most part of the drawn string. */
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nscoord descent;
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/* The vertical distance from the origin of the drawing
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operation to the bottom-most part of the drawn string.
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The _exact_ height of the string is therefore:
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ascent + descent */
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nscoord width;
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/* The horizontal distance from the origin of the drawing
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operation to the correct origin for drawing another string
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to follow the current one. Depending on the font, this
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could be greater than or less than the right bearing. */
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nsBoundingMetrics() : leftBearing(0), rightBearing(0),
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ascent(0), descent(0), width(0)
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{}
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void
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operator += (const nsBoundingMetrics& bm) {
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if (ascent + descent == 0 && rightBearing - leftBearing == 0) {
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ascent = bm.ascent;
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descent = bm.descent;
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leftBearing = width + bm.leftBearing;
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rightBearing = width + bm.rightBearing;
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}
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else {
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if (ascent < bm.ascent) ascent = bm.ascent;
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if (descent < bm.descent) descent = bm.descent;
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leftBearing = std::min(leftBearing, width + bm.leftBearing);
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rightBearing = std::max(rightBearing, width + bm.rightBearing);
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}
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width += bm.width;
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}
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};
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#endif // __nsBoundingMetrics_h
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