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Do BiDi algorithm for text layout

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This patch extends the previous BiDi support (when the direction for the
entire string was given by the caller) to run the BiDi algorithm
(provided by ICU) over the string to break it into BiDi runs. Thus, it
handles mixed LTR and RTL strings in a single layout, and also respects
heuristics for inferring the paragraph direction from the string.

Change-Id: Ia4b869de3c139c5a7d16b8ce7766870b98a815ea
This commit is contained in:
Raph Levien
2014-05-19 11:58:20 -07:00
parent 4841666ebe
commit e9ee256331
3 changed files with 85 additions and 10 deletions
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4
engine/src/flutter/include/minikin/Layout.h
View File

@@ -94,6 +94,10 @@ private:
// Find a face in the mFaces vector, or create a new entry
int findFace(MinikinFont* face, MinikinPaint* paint);
// Lay out a single bidi run
void doLayoutRun(const uint16_t* buf, size_t start, size_t count, size_t bufSize,
bool isRtl, FontStyle style, MinikinPaint& paint);
CssProperties mProps; // TODO: want spans
std::vector<LayoutGlyph> mGlyphs;
std::vector<float> mAdvances;

3
engine/src/flutter/libs/minikin/Android.mk
View File

@@ -43,6 +43,7 @@ LOCAL_SHARED_LIBRARIES := \
liblog \
libpng \
libz \
libstlport
libstlport \
libicuuc
include $(BUILD_SHARED_LIBRARY)

88
engine/src/flutter/libs/minikin/Layout.cpp
View File

@@ -39,6 +39,21 @@ namespace android {
// TODO: globals are not cool, move to a factory-ish object
hb_buffer_t* buffer = 0;
// TODO: these should move into the header file, but for now we don't want
// to cause namespace collisions with TextLayout.h
enum {
kBidi_LTR = 0,
kBidi_RTL = 1,
kBidi_Default_LTR = 2,
kBidi_Default_RTL = 3,
kBidi_Force_LTR = 4,
kBidi_Force_RTL = 5,
kBidi_Mask = 0x7
};
const int kDirection_Mask = 0x1;
Bitmap::Bitmap(int width, int height) : width(width), height(height) {
buf = new uint8_t[width * height]();
}
@@ -291,18 +306,14 @@ void Layout::doLayout(const uint16_t* buf, size_t nchars) {
}
FT_Error error;
vector<FontCollection::Run> items;
FontStyle style = styleFromCss(mProps);
mCollection->itemize(buf, nchars, style, &items);
MinikinPaint paint;
double size = mProps.value(fontSize).getFloatValue();
paint.size = size;
int bidiFlags = mProps.hasTag(minikinBidi) ? mProps.value(minikinBidi).getIntValue() : 0;
bool isRtl = (bidiFlags & 1) != 0; // TODO: do real bidi algo
if (isRtl) {
std::reverse(items.begin(), items.end());
}
bool isRtl = (bidiFlags & kDirection_Mask) != 0;
bool doSingleRun = true;
mGlyphs.clear();
mFaces.clear();
@@ -310,7 +321,65 @@ void Layout::doLayout(const uint16_t* buf, size_t nchars) {
mBounds.setEmpty();
mAdvances.clear();
mAdvances.resize(nchars, 0);
float x = 0;
mAdvance = 0;
if (!(bidiFlags == kBidi_Force_LTR || bidiFlags == kBidi_Force_RTL)) {
UBiDi* bidi = ubidi_open();
if (bidi) {
UErrorCode status = U_ZERO_ERROR;
UBiDiLevel bidiReq = bidiFlags;
if (bidiFlags == kBidi_Default_LTR) {
bidiReq = UBIDI_DEFAULT_LTR;
} else if (bidiFlags == kBidi_Default_RTL) {
bidiReq = UBIDI_DEFAULT_RTL;
}
ubidi_setPara(bidi, buf, nchars, bidiReq, NULL, &status);
if (U_SUCCESS(status)) {
int paraDir = ubidi_getParaLevel(bidi) & kDirection_Mask;
ssize_t rc = ubidi_countRuns(bidi, &status);
if (!U_SUCCESS(status) || rc < 1) {
ALOGD("error counting bidi runs, status = %d", status);
}
if (!U_SUCCESS(status) || rc <= 1) {
isRtl = (paraDir == kBidi_RTL);
} else {
doSingleRun = false;
// iterate through runs
for (ssize_t i = 0; i < (ssize_t)rc; i++) {
int32_t startRun = -1;
int32_t lengthRun = -1;
UBiDiDirection runDir = ubidi_getVisualRun(bidi, i, &startRun, &lengthRun);
if (startRun == -1 || lengthRun == -1) {
ALOGE("invalid visual run");
// Note: this case will lose text; can it ever actually happen?
break;
}
isRtl = (runDir == UBIDI_RTL);
// TODO: min/max with context
doLayoutRun(buf, startRun, lengthRun, nchars, isRtl, style, paint);
}
}
} else {
ALOGE("error calling ubidi_setPara, status = %d", status);
}
ubidi_close(bidi);
} else {
ALOGE("error creating bidi object");
}
}
if (doSingleRun) {
doLayoutRun(buf, 0, nchars, nchars, isRtl, style, paint);
}
}
void Layout::doLayoutRun(const uint16_t* buf, size_t start, size_t count, size_t bufSize,
bool isRtl, FontStyle style, MinikinPaint& paint) {
vector<FontCollection::Run> items;
mCollection->itemize(buf + start, count, style, &items);
if (isRtl) {
std::reverse(items.begin(), items.end());
}
float x = mAdvance;
float y = 0;
for (size_t run_ix = 0; run_ix < items.size(); run_ix++) {
FontCollection::Run &run = items[run_ix];
@@ -325,6 +394,7 @@ void Layout::doLayout(const uint16_t* buf, size_t nchars) {
std::cout << "Run " << run_ix << ", font " << font_ix <<
" [" << run.start << ":" << run.end << "]" << std::endl;
#endif
double size = paint.size;
hb_font_set_ppem(hbFont, size, size);
hb_font_set_scale(hbFont, HBFloatToFixed(size), HBFloatToFixed(size));
@@ -334,12 +404,12 @@ void Layout::doLayout(const uint16_t* buf, size_t nchars) {
ssize_t srunend;
for (ssize_t srunstart = run.start; srunstart < run.end; srunstart = srunend) {
srunend = srunstart;
hb_script_t script = getScriptRun(buf, run.end, &srunend);
hb_script_t script = getScriptRun(buf + start, run.end, &srunend);
hb_buffer_reset(buffer);
hb_buffer_set_script(buffer, script);
hb_buffer_set_direction(buffer, isRtl? HB_DIRECTION_RTL : HB_DIRECTION_LTR);
hb_buffer_add_utf16(buffer, buf, nchars, srunstart, srunend - srunstart);
hb_buffer_add_utf16(buffer, buf, bufSize, srunstart + start, srunend - srunstart);
hb_shape(hbFont, buffer, NULL, 0);
unsigned int numGlyphs;
hb_glyph_info_t *info = hb_buffer_get_glyph_infos(buffer, &numGlyphs);