I'm migrating some code from ATSUI to Core Text. It's pretty raw stuff, i.e. it does all the layouting itself and only uses ATSUI/Core Text to draw single lines of text to raw pixel buffers and obtain measurements.
The raw pixel data emitted by ATSUDrawText() and CTLineDraw() seems to match
exactly.
Also, the measurements returned by ATSUI/Core Text seem to match most of the
time. Thus,
it's usually the case that the pixels in text generated using ATSUI match
exactly the
text pixels generated by Core Text.
That's nice to see and I didn't expect that but it activated a perfectionist
tendency
in me so that I ran some hardcore tests with lots of different texts printed in
different
sizes and layouts to see if I could find a deviation between ATSUI and Core
Text. And I
did ;) It happens only in very rare cases but sometimes the cursor advance
returned by
ATSUI is a pixel off from the cursor advance returned by Core Text. But only
very
seldomly. However, in complex layouts this can then accumulate and lead to an
entirely
different layout if wordwrapping is involved.
That's why I'd like to ask the question if there is a way around this. Here are
the
relevant code pieces:
---------------------------------------------------------------------------
CTFontRef font = CTFontCreateWithName(CFSTR("Arial"), 39, NULL);
CFStringRef keys[] = {kCTFontAttributeName};
CFTypeRef values[] = {font};
CFDictionaryRef attr = CFDictionaryCreate(NULL, (const void **) &keys,
(const void **) &values, 1, &kCFTypeDictionaryKeyCallBacks,
&kCFTypeDictionaryValueCallBacks);
CFAttributedStringRef attrString = CFAttributedStringCreate(NULL,
CFSTR("W"), attr);
CTLineRef line = CTLineCreateWithAttributedString(attrString);
CGFloat cursor_advance = CTLineGetOffsetForStringIndex(line, 1, NULL);
printf("CORE TEXT: %.14g\n", cursor_advance);
CFRelease(line);
CFRelease(attrString);
CFRelease(attr);
CFRelease(font);
---------------------------------------------------------------------------
ATSUFontID fontID;
ATSUStyle style;
ATSUTextLayout tl;
ATSUAttributeTag styleTags[2];
ATSUAttributeValuePtr styleValues[2];
ByteCount styleSizes[2];
Fixed fsize;
UniChar textbuf[] = {'W'};
UniCharArrayOffset newOffset;
ATSUCaret mainCaret, secondCaret;
Boolean caretIsSplit;
ATSUCreateStyle(&style);
ATSUCreateTextLayout(&tl);
ATSUFindFontFromName("Arial", 5, kFontFullName, kFontNoPlatform,
kFontRomanScript, kFontNoLanguageCode, &fontID);
styleTags[0] = kATSUFontTag;
styleTags[1] = kATSUSizeTag;
fsize = FloatToFixed(39);
styleValues[0] = &fontID;
styleValues[1] = &fsize;
styleSizes[0] = sizeof(ATSUFontID);
styleSizes[1] = sizeof(Fixed);
ATSUSetAttributes(style, 2, styleTags, styleSizes, styleValues);
ATSUSetTextPointerLocation(tl, textbuf, 0, 1, 1);
ATSUSetRunStyle(tl, style, kATSUFromTextBeginning, kATSUToTextEnd);
ATSURightwardCursorPosition(tl, 1, kATSUByCharacter, &newOffset);
ATSUOffsetToPosition(tl, newOffset, TRUE, &mainCaret, &secondCaret,
&caretIsSplit);
printf("ATSUI: %.14g\n", (double) FixedToFloat(mainCaret.fX));
ATSUDisposeTextLayout(tl);
ATSUDisposeStyle(style);
---------------------------------------------------------------------------
Both code snippets calculate the cursor advance after the "W" character in
Arial, 39pt. These are the results:
CORE TEXT: 36.81005859375
ATSUI: 38
As you can see, ATSUI demands a slightly higher advance than Core Text.
Do you think it is possible to make ATSUI and Core Text return *identical*
cursor
advancements for all fonts and sizes?
Full example program attached for reference.
--
Best regards,
Andreas Falkenhahn mailto:[email protected]
main.c
Description: Binary data
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