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More consistent conversion of lengths to pixels.

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We now calculate the nearest whole number of pixels required for 1 unit, then multiply that by the requested length.
This means that 2 * len2px(1, cm) == len2px(2, cm), for example.

svn path=/trunk/netsurf/; revision=8782
This commit is contained in:
John Mark Bell 2009-07-25 13:19:11 +00:00
parent 3c8f684145
commit 2939ec04de
1 changed files with 34 additions and 15 deletions
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49
css/utils.c
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@ -74,7 +74,7 @@ css_fixed nscss_len2px(css_fixed length, css_unit unit,
const css_computed_style *style)
{
/* We assume the screen and any other output has the same dpi */
const css_fixed lendpi = FMUL(length, nscss_screen_dpi);
css_fixed px_per_unit;
assert(style != NULL || (unit != CSS_UNIT_EM && unit != CSS_UNIT_EX));
@ -95,30 +95,49 @@ css_fixed nscss_len2px(css_fixed length, css_unit unit,
font_size = FDIVI(INTTOFIX(option_font_min_size), 10);
}
/* Expand relative length */
length = FMUL(length,
nscss_len2px(font_size, CSS_UNIT_PT, style));
/* Convert to pixels (manually, to maximise precision)
* 1in = 72pt => 1pt = (DPI/72)px */
px_per_unit = FDIV(FMUL(font_size, nscss_screen_dpi),
INTTOFIX(72));
/* Scale ex units: we use a fixed ratio of 1ex = 0.6em */
if (unit == CSS_UNIT_EX)
length = FMUL(length, FLTTOFIX(0.6));
return length;
px_per_unit = FMUL(px_per_unit, FLTTOFIX(0.6));
}
case CSS_UNIT_PX: return length;
break;
case CSS_UNIT_PX:
px_per_unit = INTTOFIX(1);
break;
/* 1in = DPIpx */
case CSS_UNIT_IN: return lendpi;
case CSS_UNIT_IN:
px_per_unit = nscss_screen_dpi;
break;
/* 1in = 2.54cm => 1cm = (DPI/2.54)px */
case CSS_UNIT_CM: return FDIV(lendpi, FLTTOFIX(2.54));
case CSS_UNIT_CM:
px_per_unit = FDIV(nscss_screen_dpi, FLTTOFIX(2.54));
break;
/* 1in = 25.4mm => 1mm = (DPI/25.4)px */
case CSS_UNIT_MM: return FDIV(lendpi, FLTTOFIX(25.4));
case CSS_UNIT_MM:
px_per_unit = FDIV(nscss_screen_dpi, FLTTOFIX(25.4));
break;
/* 1in = 72pt => 1pt = (DPI/72)px */
case CSS_UNIT_PT: return FDIV(lendpi, INTTOFIX(72));
case CSS_UNIT_PT:
px_per_unit = FDIV(nscss_screen_dpi, INTTOFIX(72));
break;
/* 1pc = 12pt => 1in = 6pc => 1pc = (DPI/6)px */
case CSS_UNIT_PC: return FDIV(lendpi, INTTOFIX(6));
default: break;
case CSS_UNIT_PC:
px_per_unit = FDIV(nscss_screen_dpi, INTTOFIX(6));
break;
default:
px_per_unit = 0;
break;
}
return 0;
/* Ensure we round px_per_unit to the nearest whole number of pixels:
* the use of FIXTOINT() below will truncate. */
px_per_unit += FDIVI(INTTOFIX(1), 2);
/* Calculate total number of pixels */
return FMULI(length, FIXTOINT(px_per_unit));
}