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Break regional indicators at even numbered code points.

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Bug: 23288449
Change-Id: If1419ff9e44e8e640616979bae88311f414b42a1
This commit is contained in:
Seigo Nonaka
2016-03-02 13:53:54 -08:00
parent a58530bccc
commit f4c679ca68
2 changed files with 34 additions and 9 deletions
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27
engine/src/flutter/libs/minikin/GraphemeBreak.cpp
View File

@@ -15,6 +15,7 @@
*/
#include <stdint.h>
#include <algorithm>
#include <unicode/uchar.h>
#include <unicode/utf16.h>
@@ -124,17 +125,25 @@ bool GraphemeBreak::isGraphemeBreak(const uint16_t* buf, size_t start, size_t co
if ((p1 == U_GCB_LVT || p1 == U_GCB_T) && p2 == U_GCB_T) {
return false;
}
// Rule GB8a, Regional_Indicator x Regional_Indicator
// Rule GB8a that looks at even-off cases.
//
// Known limitation: This is overly conservative, and returns no grapheme breaks between two
// flags, such as in the character sequence "U+1F1FA U+1F1F8 [potential break] U+1F1FA U+1F1F8".
// Also, it assumes that all combinations of Regional Indicators produce a flag, where they
// don't.
//
// There is no easy solution for doing this correctly, except for querying the font and doing
// some lookback.
// sot (RI RI)* RI x RI
// [^RI] (RI RI)* RI x RI
// RI ÷ RI
if (p1 == U_GCB_REGIONAL_INDICATOR && p2 == U_GCB_REGIONAL_INDICATOR) {
return false;
// Look at up to 1000 code units.
start = std::max((ssize_t)start, (ssize_t)offset_back - 1000);
while (offset_back > start) {
U16_PREV(buf, start, offset_back, c1);
if (tailoredGraphemeClusterBreak(c1) != U_GCB_REGIONAL_INDICATOR) {
offset_back += U16_LENGTH(c1);
break;
}
}
// Note that the offset has moved forwared 2 code units by U16_NEXT.
// The number 4 comes from the number of code units in a whole flag.
return (offset - 2 - offset_back) % 4 == 0;
}
// Rule GB9, x Extend; Rule GB9a, x SpacingMark; Rule GB9b, Prepend x
if (p2 == U_GCB_EXTEND || p2 == U_GCB_SPACING_MARK || p1 == U_GCB_PREPEND) {

16
engine/src/flutter/tests/GraphemeBreakTests.cpp
View File

@@ -84,6 +84,22 @@ TEST(GraphemeBreak, rules) {
// Rule GB8a, Regional_Indicator x Regional_Indicator
EXPECT_FALSE(IsBreak("U+1F1FA | U+1F1F8"));
EXPECT_TRUE(IsBreak("U+1F1FA U+1F1F8 | U+1F1FA U+1F1F8")); // Regional indicator pair (flag)
EXPECT_FALSE(IsBreak("U+1F1FA | U+1F1F8 U+1F1FA U+1F1F8")); // Regional indicator pair (flag)
EXPECT_FALSE(IsBreak("U+1F1FA U+1F1F8 U+1F1FA | U+1F1F8")); // Regional indicator pair (flag)
EXPECT_TRUE(IsBreak("U+1F1FA U+1F1F8 | U+1F1FA")); // Regional indicator pair (flag)
EXPECT_FALSE(IsBreak("U+1F1FA | U+1F1F8 U+1F1FA")); // Regional indicator pair (flag)
EXPECT_TRUE(IsBreak("'a' U+1F1FA U+1F1F8 | U+1F1FA")); // Regional indicator pair (flag)
EXPECT_FALSE(IsBreak("'a' U+1F1FA | U+1F1F8 U+1F1FA")); // Regional indicator pair (flag)
EXPECT_TRUE(
IsBreak("'a' U+1F1FA U+1F1F8 | U+1F1FA U+1F1F8")); // Regional indicator pair (flag)
EXPECT_FALSE(
IsBreak("'a' U+1F1FA | U+1F1F8 U+1F1FA U+1F1F8")); // Regional indicator pair (flag)
EXPECT_FALSE(
IsBreak("'a' U+1F1FA U+1F1F8 U+1F1FA | U+1F1F8")); // Regional indicator pair (flag)
// Rule GB9, x Extend
EXPECT_FALSE(IsBreak("'a' | U+0301")); // combining accent