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Snap advance widths to integers

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Fractional advance widths were causing subtle problems with text
positioning when the same text was drawn with different spans in the
hwui renderer. Quantizing the coordinates on layout (as opposed to
waiting until the renderer draws the glyphs) solves the problem.

This patch also fixes a discrepancy between x position and advance
widths when letterspacing.

Bug: 17347779
Change-Id: Ia705944047408c2839d5ad078eefd6bbec446872
This commit is contained in:
Raph Levien
2014-09-03 10:37:05 -07:00
parent 543c65c80b
commit ff55a581fa
2 changed files with 24 additions and 8 deletions
Download Patch File Download Diff File Expand all files Collapse all files

6
engine/src/flutter/include/minikin/MinikinFont.h
View File

@@ -49,6 +49,12 @@ struct MinikinPaint {
std::string fontFeatureSettings; std::string fontFeatureSettings;
}; };
// Only a few flags affect layout, but those that do should have values
// consistent with Android's paint flags.
enum MinikinPaintFlags {
LinearTextFlag = 0x40,
};
struct MinikinRect { struct MinikinRect {
float mLeft, mTop, mRight, mBottom; float mLeft, mTop, mRight, mBottom;
bool isEmpty() const { bool isEmpty() const {

26
engine/src/flutter/libs/minikin/Layout.cpp
View File

@@ -676,7 +676,14 @@ void Layout::doLayoutRun(const uint16_t* buf, size_t start, size_t count, size_t
double size = ctx->paint.size; double size = ctx->paint.size;
double scaleX = ctx->paint.scaleX; double scaleX = ctx->paint.scaleX;
double letterSpace = ctx->paint.letterSpacing * size * scaleX; double letterSpace = ctx->paint.letterSpacing * size * scaleX;
double letterSpaceHalf = letterSpace * .5; double letterSpaceHalfLeft;
if ((ctx->paint.paintFlags & LinearTextFlag) == 0) {
letterSpace = round(letterSpace);
letterSpaceHalfLeft = floor(letterSpace * 0.5);
} else {
letterSpaceHalfLeft = letterSpace * 0.5;
}
double letterSpaceHalfRight = letterSpace - letterSpaceHalfLeft;
float x = mAdvance; float x = mAdvance;
float y = 0; float y = 0;
@@ -721,8 +728,8 @@ void Layout::doLayoutRun(const uint16_t* buf, size_t start, size_t count, size_t
hb_glyph_position_t* positions = hb_buffer_get_glyph_positions(buffer, NULL); hb_glyph_position_t* positions = hb_buffer_get_glyph_positions(buffer, NULL);
if (numGlyphs) if (numGlyphs)
{ {
mAdvances[info[0].cluster - start] += letterSpaceHalf; mAdvances[info[0].cluster - start] += letterSpaceHalfLeft;
x += letterSpaceHalf; x += letterSpaceHalfLeft;
} }
for (unsigned int i = 0; i < numGlyphs; i++) { for (unsigned int i = 0; i < numGlyphs; i++) {
#ifdef VERBOSE #ifdef VERBOSE
@@ -730,9 +737,9 @@ void Layout::doLayoutRun(const uint16_t* buf, size_t start, size_t count, size_t
": " << HBFixedToFloat(positions[i].x_advance) << "; " << positions[i].x_offset << ", " << positions[i].y_offset << std::endl; ": " << HBFixedToFloat(positions[i].x_advance) << "; " << positions[i].x_offset << ", " << positions[i].y_offset << std::endl;
#endif #endif
if (i > 0 && info[i - 1].cluster != info[i].cluster) { if (i > 0 && info[i - 1].cluster != info[i].cluster) {
mAdvances[info[i - 1].cluster - start] += letterSpaceHalf; mAdvances[info[i - 1].cluster - start] += letterSpaceHalfRight;
mAdvances[info[i].cluster - start] += letterSpaceHalf; mAdvances[info[i].cluster - start] += letterSpaceHalfLeft;
x += letterSpaceHalf; x += letterSpace;
} }
hb_codepoint_t glyph_ix = info[i].codepoint; hb_codepoint_t glyph_ix = info[i].codepoint;
@@ -742,6 +749,9 @@ void Layout::doLayoutRun(const uint16_t* buf, size_t start, size_t count, size_t
LayoutGlyph glyph = {font_ix, glyph_ix, x + xoff, y + yoff}; LayoutGlyph glyph = {font_ix, glyph_ix, x + xoff, y + yoff};
mGlyphs.push_back(glyph); mGlyphs.push_back(glyph);
float xAdvance = HBFixedToFloat(positions[i].x_advance); float xAdvance = HBFixedToFloat(positions[i].x_advance);
if ((ctx->paint.paintFlags & LinearTextFlag) == 0) {
xAdvance = roundf(xAdvance);
}
MinikinRect glyphBounds; MinikinRect glyphBounds;
ctx->paint.font->GetBounds(&glyphBounds, glyph_ix, ctx->paint); ctx->paint.font->GetBounds(&glyphBounds, glyph_ix, ctx->paint);
glyphBounds.offset(x + xoff, y + yoff); glyphBounds.offset(x + xoff, y + yoff);
@@ -751,8 +761,8 @@ void Layout::doLayoutRun(const uint16_t* buf, size_t start, size_t count, size_t
} }
if (numGlyphs) if (numGlyphs)
{ {
mAdvances[info[numGlyphs - 1].cluster - start] += letterSpaceHalf; mAdvances[info[numGlyphs - 1].cluster - start] += letterSpaceHalfRight;
x += letterSpaceHalf; x += letterSpaceHalfRight;
} }
} }
} }