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b=605043 round inter-glyph spacing to pixels when glyphs will be pixel snapped r=jfkthame

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This commit is contained in:
Karl Tomlinson 2010-11-15 08:21:37 +13:00
parent 1075ede261
commit 20b116d1d6
1 changed files with 109 additions and 9 deletions
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118
gfx/thebes/gfxHarfBuzzShaper.cpp
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@ -52,11 +52,18 @@
#include "harfbuzz/hb-unicode.h"
#include "harfbuzz/hb-ot.h"
#include "cairo.h"
#include "nsUnicodeRange.h"
#include "nsCRT.h"
#define FloatToFixed(f) (65536 * (f))
#define FixedToFloat(f) ((f) * (1.0 / 65536.0))
// Right shifts of negative (signed) integers are undefined, as are overflows
// when converting unsigned to negative signed integers.
// (If speed were an issue we could make some 2's complement assumptions.)
#define FixedToIntRound(f) ((f) > 0 ? ((32768 + (f)) >> 16) \
: -((32767 - (f)) >> 16))
using namespace mozilla; // for AutoSwap_* types
@ -871,6 +878,73 @@ gfxHarfBuzzShaper::InitTextRun(gfxContext *aContext,
return PR_TRUE;
}
/**
* Work out whether cairo will snap inter-glyph spacing to pixels.
*
* Layout does not align text to pixel boundaries, so, with font drawing
* backends that snap glyph positions to pixels, it is important that
* inter-glyph spacing within words is always an integer number of pixels.
* This ensures that the drawing backend snaps all of the word's glyphs in the
* same direction and so inter-glyph spacing remains the same.
*/
static void
GetRoundOffsetsToPixels(gfxContext *aContext,
PRBool *aRoundX, PRBool *aRoundY)
{
*aRoundX = PR_FALSE;
// Could do something fancy here for ScaleFactors of
// AxisAlignedTransforms, but we leave things simple.
// Not much point rounding if a matrix will mess things up anyway.
if (aContext->CurrentMatrix().HasNonTranslation()) {
*aRoundY = PR_FALSE;
return;
}
// All raster backends snap glyphs to pixels vertically.
// Print backends set CAIRO_HINT_METRICS_OFF.
*aRoundY = PR_TRUE;
cairo_t *cr = aContext->GetCairo();
cairo_scaled_font_t *scaled_font = cairo_get_scaled_font(cr);
// Sometimes hint metrics gets set for us, most notably for printing.
cairo_font_options_t *font_options = cairo_font_options_create();
cairo_scaled_font_get_font_options(scaled_font, font_options);
cairo_hint_metrics_t hint_metrics =
cairo_font_options_get_hint_metrics(font_options);
cairo_font_options_destroy(font_options);
switch (hint_metrics) {
case CAIRO_HINT_METRICS_OFF:
*aRoundY = PR_FALSE;
return;
case CAIRO_HINT_METRICS_DEFAULT:
// Here we mimic what cairo surface/font backends do. Printing
// surfaces have already been handled by hint_metrics. The
// fallback show_glyphs implementation composites pixel-aligned
// glyph surfaces, so we just pick surface/font combinations that
// override this.
switch (cairo_scaled_font_get_type(scaled_font)) {
case CAIRO_FONT_TYPE_DWRITE:
// show_glyphs is implemented on the font and so is used for
// all surface types.
return;
case CAIRO_FONT_TYPE_QUARTZ:
// Quartz surfaces implement show_glyphs for Quartz fonts
if (cairo_surface_get_type(cairo_get_target(cr)) ==
CAIRO_SURFACE_TYPE_QUARTZ) {
return;
}
default:
break;
}
// fall through:
case CAIRO_HINT_METRICS_ON:
break;
}
*aRoundX = PR_TRUE;
return;
}
#define SMALL_GLYPH_RUN 128 // some testing indicates that 90%+ of text runs
// will fit without requiring separate allocation
// for charToGlyphArray
@ -910,8 +984,14 @@ gfxHarfBuzzShaper::SetGlyphsFromRun(gfxContext *aContext,
PRInt32 glyphStart = 0; // looking for a clump that starts at this glyph
PRInt32 charStart = 0; // and this char index within the range of the run
PRBool roundX;
PRBool roundY;
GetRoundOffsetsToPixels(aContext, &roundX, &roundY);
// This is signed to avoid promotion to unsigned.
PRInt32 dev2appUnits = aTextRun->GetAppUnitsPerDevUnit();
// factor to convert 16.16 fixed-point pixels to app units
float hb2appUnits = aTextRun->GetAppUnitsPerDevUnit() / 65536.0;
// (only used if not rounding)
double hb2appUnits = FixedToFloat(aTextRun->GetAppUnitsPerDevUnit());
// keep track of y-position to set glyph offsets if needed
nscoord yPos = 0;
@ -1014,7 +1094,11 @@ gfxHarfBuzzShaper::SetGlyphsFromRun(gfxContext *aContext,
}
// Check if it's a simple one-to-one mapping
nscoord advance = NS_roundf(hb2appUnits * posInfo[glyphStart].x_advance);
hb_position_t x_advance = posInfo[glyphStart].x_advance;
nscoord advance =
roundX ? dev2appUnits * FixedToIntRound(x_advance)
: NS_floor(hb2appUnits * x_advance + 0.5);
if (glyphsInClump == 1 &&
gfxTextRun::CompressedGlyph::IsSimpleGlyphID(ginfo[glyphStart].codepoint) &&
gfxTextRun::CompressedGlyph::IsSimpleAdvance(advance) &&
@ -1035,18 +1119,34 @@ gfxHarfBuzzShaper::SetGlyphsFromRun(gfxContext *aContext,
gfxTextRun::DetailedGlyph* details =
detailedGlyphs.AppendElement();
details->mGlyphID = ginfo[glyphStart].codepoint;
details->mXOffset = posInfo[glyphStart].x_offset == 0 ?
0 : hb2appUnits * posInfo[glyphStart].x_offset;
details->mYOffset = yPos - (posInfo[glyphStart].y_offset == 0 ?
0 : hb2appUnits * posInfo[glyphStart].y_offset);
// Rounding offsets independently of advances on the assumption
// that clusters use offsets and rounding of offsets should
// not accumulate, and that advances are typically between
// clusters.
hb_position_t x_offset = posInfo[glyphStart].x_offset;
details->mXOffset =
roundX ? dev2appUnits * FixedToIntRound(x_offset)
: NS_floor(hb2appUnits * x_offset + 0.5);
hb_position_t y_offset = posInfo[glyphStart].y_offset;
details->mYOffset = yPos -
roundY ? dev2appUnits * FixedToIntRound(y_offset)
: NS_floor(hb2appUnits * y_offset + 0.5);
details->mAdvance = advance;
if (posInfo[glyphStart].y_advance != 0) {
yPos -= hb2appUnits * posInfo[glyphStart].y_advance;
hb_position_t y_advance = posInfo[glyphStart].y_advance;
if (y_advance != 0) {
yPos -=
roundY ? dev2appUnits * FixedToIntRound(y_advance)
: NS_floor(hb2appUnits * y_advance + 0.5);
}
if (++glyphStart >= glyphEnd) {
break;
}
advance = NS_roundf(hb2appUnits * posInfo[glyphStart].x_advance);
x_advance = posInfo[glyphStart].x_advance;
advance =
roundX ? dev2appUnits * FixedToIntRound(x_advance)
: NS_floor(hb2appUnits * x_advance + 0.5);
}
gfxTextRun::CompressedGlyph g;