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37 :
38 : #ifndef __nsBoundingMetrics_h
39 : #define __nsBoundingMetrics_h
40 :
41 : #include "nsCoord.h"
42 :
43 : /* Struct used for accurate measurements of a string, in order to
44 : * allow precise positioning when processing MathML. This is in its
45 : * own header file because some very-widely-included headers need it
46 : * but not the rest of nsFontMetrics, or vice versa.
47 : */
48 :
49 : struct nsBoundingMetrics {
50 :
51 : ///////////
52 : // Metrics that _exactly_ enclose the text:
53 :
54 : // The character coordinate system is the one used on X Windows:
55 : // 1. The origin is located at the intersection of the baseline
56 : // with the left of the character's cell.
57 : // 2. All horizontal bearings are oriented from left to right.
58 : // 2. All horizontal bearings are oriented from left to right.
59 : // 3. The ascent is oriented from bottom to top (being 0 at the orgin).
60 : // 4. The descent is oriented from top to bottom (being 0 at the origin).
61 :
62 : // Note that Win32/Mac/PostScript use a different convention for
63 : // the descent (all vertical measurements are oriented from bottom
64 : // to top on these palatforms). Make sure to flip the sign of the
65 : // descent on these platforms for cross-platform compatibility.
66 :
67 : // Any of the following member variables listed here can have
68 : // positive or negative value.
69 :
70 : nscoord leftBearing;
71 : /* The horizontal distance from the origin of the drawing
72 : operation to the left-most part of the drawn string. */
73 :
74 : nscoord rightBearing;
75 : /* The horizontal distance from the origin of the drawing
76 : operation to the right-most part of the drawn string.
77 : The _exact_ width of the string is therefore:
78 : rightBearing - leftBearing */
79 :
80 : nscoord ascent;
81 : /* The vertical distance from the origin of the drawing
82 : operation to the top-most part of the drawn string. */
83 :
84 : nscoord descent;
85 : /* The vertical distance from the origin of the drawing
86 : operation to the bottom-most part of the drawn string.
87 : The _exact_ height of the string is therefore:
88 : ascent + descent */
89 :
90 : nscoord width;
91 : /* The horizontal distance from the origin of the drawing
92 : operation to the correct origin for drawing another string
93 : to follow the current one. Depending on the font, this
94 : could be greater than or less than the right bearing. */
95 :
96 0 : nsBoundingMetrics() : leftBearing(0), rightBearing(0),
97 0 : ascent(0), descent(0), width(0)
98 0 : {}
99 :
100 : void
101 0 : operator += (const nsBoundingMetrics& bm) {
102 0 : if (ascent + descent == 0 && rightBearing - leftBearing == 0) {
103 0 : ascent = bm.ascent;
104 0 : descent = bm.descent;
105 0 : leftBearing = width + bm.leftBearing;
106 0 : rightBearing = width + bm.rightBearing;
107 : }
108 : else {
109 0 : if (ascent < bm.ascent) ascent = bm.ascent;
110 0 : if (descent < bm.descent) descent = bm.descent;
111 0 : leftBearing = NS_MIN(leftBearing, width + bm.leftBearing);
112 0 : rightBearing = NS_MAX(rightBearing, width + bm.rightBearing);
113 : }
114 0 : width += bm.width;
115 0 : }
116 : };
117 :
118 : #endif // __nsBoundingMetrics_h
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