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