libui/darwin/drawtext.m

// 2 january 2017
#import "uipriv_darwin.h"
#import "draw.h"

// TODO what happens if nLines == 0 in any function?

struct uiDrawTextLayout {
	CFAttributedStringRef attrstr;

	// the width as passed into uiDrawTextLayout constructors
	double width;

	CTFramesetterRef framesetter;

	// the *actual* size of the frame
	// note: technically, metrics returned from frame are relative to CGPathGetPathBoundingBox(tl->path)
	// however, from what I can gather, for a path created by CGPathCreateWithRect(), like we do (with a NULL transform), CGPathGetPathBoundingBox() seems to just return the standardized form of the rect used to create the path
	// (this I confirmed through experimentation)
	// so we can just use tl->size for adjustments
	// we don't need to adjust coordinates by any origin since our rect origin is (0, 0)
	CGSize size;

	CGPathRef path;
	CTFrameRef frame;

	CFArrayRef lines;
	CFIndex nLines;
	// we compute this once when first creating the layout
	uiDrawTextLayoutLineMetrics *lineMetrics;

	// for converting CFAttributedString indices from/to byte offsets
	size_t *u8tou16;
	size_t nUTF8;
	size_t *u16tou8;
	size_t nUTF16;
};

static CTFontRef fontdescToCTFont(uiDrawFontDescriptor *fd)
{
	CTFontDescriptorRef desc;
	CTFontRef font;

	desc = fontdescToCTFontDescriptor(fd);
	font = CTFontCreateWithFontDescriptor(desc, fd->Size, NULL);
	CFRelease(desc);			// TODO correct?
	return font;
}

static CFAttributedStringRef attrstrToCoreFoundation(uiAttributedString *s, uiDrawFontDescriptor *defaultFont)
{
	CFStringRef cfstr;
	CFMutableDictionaryRef defaultAttrs;
	CTFontRef defaultCTFont;
	CFAttributedStringRef base;
	CFMutableAttributedStringRef mas;

	cfstr = CFStringCreateWithCharacters(NULL, attrstrUTF16(s), attrstrUTF16Len(s));
	if (cfstr == NULL) {
		// TODO
	}
	defaultAttrs = CFDictionaryCreateMutable(NULL, 1,
		&kCFCopyStringDictionaryKeyCallBacks,
		&kCFTypeDictionaryValueCallBacks);
	if (defaultAttrs == NULL) {
		// TODO
	}
	defaultCTFont = fontdescToCTFont(defaultFont);
	CFDictionaryAddValue(defaultAttrs, kCTFontAttributeName, defaultCTFont);
	CFRelease(defaultCTFont);

	base = CFAttributedStringCreate(NULL, cfstr, defaultAttrs);
	if (base == NULL) {
		// TODO
	}
	CFRelease(cfstr);
	CFRelease(defaultAttrs);
	mas = CFAttributedStringCreateMutableCopy(NULL, 0, base);
	CFRelease(base);

	CFAttributedStringBeginEditing(mas);
	// TODO copy in the attributes
	CFAttributedStringEndEditing(mas);

	return mas;
}

// TODO this is wrong for our hit-test example's multiple combining character example
static uiDrawTextLayoutLineMetrics *computeLineMetrics(CTFrameRef frame, CGSize size)
{
	uiDrawTextLayoutLineMetrics *metrics;
	CFArrayRef lines;
	CTLineRef line;
	CFIndex i, n;
	CGFloat ypos;
	CGRect bounds, boundsNoLeading;
	CGFloat ascent, descent, leading;
	CGPoint *origins;

	lines = CTFrameGetLines(frame);
	n = CFArrayGetCount(lines);
	metrics = (uiDrawTextLayoutLineMetrics *) uiAlloc(n * sizeof (uiDrawTextLayoutLineMetrics), "uiDrawTextLayoutLineMetrics[] (text layout)");

	origins = (CGPoint *) uiAlloc(n * sizeof (CGPoint), "CGPoint[] (text layout)");
	CTFrameGetLineOrigins(frame, CFRangeMake(0, n), origins);

	ypos = size.height;
	for (i = 0; i < n; i++) {
		line = (CTLineRef) CFArrayGetValueAtIndex(lines, i);
		bounds = CTLineGetBoundsWithOptions(line, 0);
		boundsNoLeading = CTLineGetBoundsWithOptions(line, kCTLineBoundsExcludeTypographicLeading);

		// this is equivalent to boundsNoLeading.size.height + boundsNoLeading.origin.y (manually verified)
		ascent = bounds.size.height + bounds.origin.y;
		descent = -boundsNoLeading.origin.y;
		// TODO does this preserve leading sign?
		leading = -bounds.origin.y - descent;

		// Core Text always rounds these up for paragraph style calculations; there is a flag to control it but it's inaccessible (and this behavior is turned off for old versions of iPhoto)
		ascent = floor(ascent + 0.5);
		descent = floor(descent + 0.5);
		if (leading > 0)
			leading = floor(leading + 0.5);

		metrics[i].X = origins[i].x;
		metrics[i].Y = origins[i].y - descent - leading;
		metrics[i].Width = bounds.size.width;
		metrics[i].Height = ascent + descent + leading;

		metrics[i].BaselineY = origins[i].y;
		metrics[i].Ascent = ascent;
		metrics[i].Descent = descent;
		metrics[i].Leading = leading;

		// TODO
		metrics[i].ParagraphSpacingBefore = 0;
		metrics[i].LineHeightSpace = 0;
		metrics[i].LineSpacing = 0;
		metrics[i].ParagraphSpacing = 0;

		// and finally advance to the next line
		ypos += metrics[i].Height;
	}

	// okay, but now all these metrics are unflipped
	// we need to flip them
	for (i = 0; i < n; i++) {
		metrics[i].Y = size.height - metrics[i].Y;
		// go from bottom-left corner to top-left
		metrics[i].Y -= metrics[i].Height;
		metrics[i].BaselineY = size.height - metrics[i].BaselineY;
		// TODO also adjust by metrics[i].Height?
	}

	uiFree(origins);
	return metrics;
}

uiDrawTextLayout *uiDrawNewTextLayout(uiAttributedString *s, uiDrawFontDescriptor *defaultFont, double width)
{
	uiDrawTextLayout *tl;
	CGFloat cgwidth;
	CFRange range, unused;
	CGRect rect;

	tl = uiNew(uiDrawTextLayout);
	tl->attrstr = attrstrToCoreFoundation(s, defaultFont);
	range.location = 0;
	range.length = CFAttributedStringGetLength(tl->attrstr);
	tl->width = width;

	// TODO CTFrameProgression for RTL/LTR
	// TODO kCTParagraphStyleSpecifierMaximumLineSpacing, kCTParagraphStyleSpecifierMinimumLineSpacing, kCTParagraphStyleSpecifierLineSpacingAdjustment for line spacing
	tl->framesetter = CTFramesetterCreateWithAttributedString(tl->attrstr);
	if (tl->framesetter == NULL) {
		// TODO
	}

	cgwidth = (CGFloat) width;
	if (cgwidth < 0)
		cgwidth = CGFLOAT_MAX;
	// TODO these seem to be floor()'d or truncated?
	// TODO double check to make sure this TODO was right
	tl->size = CTFramesetterSuggestFrameSizeWithConstraints(tl->framesetter,
		range,
		// TODO kCTFramePathWidthAttributeName?
		NULL,
		CGSizeMake(cgwidth, CGFLOAT_MAX),
		&unused);			// not documented as accepting NULL (TODO really?)

	rect.origin = CGPointZero;
	rect.size = tl->size;
	tl->path = CGPathCreateWithRect(rect, NULL);
	tl->frame = CTFramesetterCreateFrame(tl->framesetter,
		range,
		tl->path,
		// TODO kCTFramePathWidthAttributeName?
		NULL);
	if (tl->frame == NULL) {
		// TODO
	}

	tl->lines = CTFrameGetLines(tl->frame);
	tl->nLines = CFArrayGetCount(tl->lines);
	tl->lineMetrics = computeLineMetrics(tl->frame, tl->size);

	// and finally copy the UTF-8/UTF-16 conversion tables
	tl->u8tou16 = attrstrCopyUTF8ToUTF16(s, &(tl->nUTF8));
	tl->u16tou8 = attrstrCopyUTF16ToUTF8(s, &(tl->nUTF16));

	return tl;
}

void uiDrawFreeTextLayout(uiDrawTextLayout *tl)
{
	uiFree(tl->u16tou8);
	uiFree(tl->u8tou16);
	uiFree(tl->lineMetrics);
	// TODO release tl->lines?
	CFRelease(tl->frame);
	CFRelease(tl->path);
	CFRelease(tl->framesetter);
	CFRelease(tl->attrstr);
	uiFree(tl);
}

// TODO document that (x,y) is the top-left corner of the *entire frame*
void uiDrawText(uiDrawContext *c, uiDrawTextLayout *tl, double x, double y)
{
	CGContextSaveGState(c->c);

	// Core Text doesn't draw onto a flipped view correctly; we have to pretend it was unflipped
	// see the iOS bits of the first example at https://developer.apple.com/library/mac/documentation/StringsTextFonts/Conceptual/CoreText_Programming/LayoutOperations/LayoutOperations.html#//apple_ref/doc/uid/TP40005533-CH12-SW1 (iOS is naturally flipped)
	// TODO how is this affected by a non-identity CTM?
	CGContextTranslateCTM(c->c, 0, c->height);
	CGContextScaleCTM(c->c, 1.0, -1.0);
	CGContextSetTextMatrix(c->c, CGAffineTransformIdentity);

	// wait, that's not enough; we need to offset y values to account for our new flipping
	// TODO explain this calculation
	y = c->height - tl->size.height - y;

	// CTFrameDraw() draws in the path we specified when creating the frame
	// this means that in our usage, CTFrameDraw() will draw at (0,0)
	// so move the origin to be at (x,y) instead
	// TODO are the signs correct?
	CGContextTranslateCTM(c->c, x, y);

	CTFrameDraw(tl->frame, c->c);

	CGContextRestoreGState(c->c);
}

// TODO document that the width and height of a layout is not necessarily the sum of the widths and heights of its constituent lines; this is definitely untrue on OS X, where lines are placed in such a way that the distance between baselines is always integral
// TODO width doesn't include trailing whitespace...
// TODO figure out how paragraph spacing should play into this
void uiDrawTextLayoutExtents(uiDrawTextLayout *tl, double *width, double *height)
{
	*width = tl->size.width;
	*height = tl->size.height;
}

int uiDrawTextLayoutNumLines(uiDrawTextLayout *tl)
{
	return tl->nLines;
}

void uiDrawTextLayoutLineByteRange(uiDrawTextLayout *tl, int line, size_t *start, size_t *end)
{
	CTLineRef lr;
	CFRange range;

	lr = (CTLineRef) CFArrayGetValueAtIndex(tl->lines, line);
	range = CTLineGetStringRange(lr);
	*start = tl->u16tou8[range.location];
	*end = tl->u16tou8[range.location + range.length];
}

void uiDrawTextLayoutLineGetMetrics(uiDrawTextLayout *tl, int line, uiDrawTextLayoutLineMetrics *m)
{
	*m = tl->lineMetrics[line];
}

// TODO note that in some cases lines can overlap slightly
// in our case, we read lines first to last and use their bottommost point (Y + Height) to determine where the next line should start for hit-testing
void uiDrawTextLayoutHitTest(uiDrawTextLayout *tl, double x, double y, uiDrawTextLayoutHitTestResult *result)
{
	CFIndex i;
	CTLineRef line;
	CFIndex pos;

	if (y >= 0) {
		for (i = 0; i < tl->nLines; i++) {
			double ltop, lbottom;

			ltop = tl->lineMetrics[i].Y;
			lbottom = ltop + tl->lineMetrics[i].Height;
			// y will already >= ltop at this point since the past lbottom should == (or at least >=, see above) ltop
			if (y < lbottom)
				break;
		}
		result->YPosition = uiDrawTextLayoutHitTestPositionInside;
		if (i == tl->nLines) {
			i--;
			result->YPosition = uiDrawTextLayoutHitTestPositionAfter;
		}
	} else {
		i = 0;
		// TODO what if the first line crosses into the negatives?
		result->YPosition = uiDrawTextLayoutHitTestPositionBefore;
	}
	result->Line = i;

	result->XPosition = uiDrawTextLayoutHitTestPositionInside;
	if (x < tl->lineMetrics[i].X) {
		result->XPosition = uiDrawTextLayoutHitTestPositionBefore;
		// and forcibly return the first character
		x = tl->lineMetrics[i].X;
	} else if (x > (tl->lineMetrics[i].X + tl->lineMetrics[i].Width)) {
		result->XPosition = uiDrawTextLayoutHitTestPositionAfter;
		// and forcibly return the last character
		x = tl->lineMetrics[i].X + tl->lineMetrics[i].Width;
	}

	line = (CTLineRef) CFArrayGetValueAtIndex(tl->lines, i);
	// TODO copy the part from the docs about this point (TODO what point?)
	pos = CTLineGetStringIndexForPosition(line, CGPointMake(x, 0));
	if (pos == kCFNotFound) {
		// TODO
	}
	result->Pos = tl->u16tou8[pos];

	// desired caret behavior: clicking on the right trailing space places inserted text at the start of the next line but the caret is on the clicked line at the trailing edge of the last grapheme
	// hitting Right moves to the second point of the next line, then Left to go to the first, then Left to go to the start of the last character of the original line (so the keyboard can't move the caret back to that clicked space)
	// this happens regardless of word-wrapping on whitespace, hyphens, or very long words
	// use CTLineGetOffsetForStringIndex() here instead of x directly as that isn't always adjusted properly
	result->CaretX = CTLineGetOffsetForStringIndex(line, pos, NULL);
	result->CaretY = tl->lineMetrics[i].Y;
	result->CaretHeight = tl->lineMetrics[i].Height;
}

// TODO document this is appropriate for a caret
// TODO what happens if we select across a wrapped line?
void uiDrawTextLayoutByteRangeToRectangle(uiDrawTextLayout *tl, size_t start, size_t end, uiDrawTextLayoutByteRangeRectangle *r)
{
	CFIndex i;
	CTLineRef line;
	CFRange range;
	CGFloat x, x2;		// TODO rename x to x1

	if (start > tl->nUTF8)
		start = tl->nUTF8;
	if (end > tl->nUTF8)
		end = tl->nUTF8;
	start = tl->u8tou16[start];
	end = tl->u8tou16[end];

	for (i = 0; i < tl->nLines; i++) {
		line = (CTLineRef) CFArrayGetValueAtIndex(tl->lines, i);
		range = CTLineGetStringRange(line);
		if (start >= range.location && start < (range.location + range.length))
			break;
	}
	if (i == tl->nLines)
		i--;
	r->Line = i;
	if (end > (range.location + range.length))
		end = range.location + range.length;

	x = CTLineGetOffsetForStringIndex(line, start, NULL);
	x2 = CTLineGetOffsetForStringIndex(line, end, NULL);

	r->X = tl->lineMetrics[i].X + x;
	r->Y = tl->lineMetrics[i].Y;
	r->Width = (tl->lineMetrics[i].X + x2) - r->X;
	r->Height = tl->lineMetrics[i].Height;

	// and use x and x2 to get the actual start and end positions
	// TODO error check?
	r->RealStart = CTLineGetStringIndexForPosition(line, CGPointMake(x, 0));
	r->RealEnd = CTLineGetStringIndexForPosition(line, CGPointMake(x2, 0));
	r->RealStart = tl->u16tou8[r->RealStart];
	r->RealEnd = tl->u16tou8[r->RealEnd];
}