Implemented Pango text metrics and expanded the drawtext basic page to draw metrics. Works on both Pango and OS X; DirectWrite comes next.

darwin/drawtext.m

@@ -246,6 +246,8 @@ void uiDrawText(uiDrawContext *c, uiDrawTextLayout *tl, double x, double y)
 }
 
 // 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;

examples/drawtext/basic.c

@@ -30,10 +30,93 @@ static uiAttributedString *attrstr;
 
 #define margins 10
 
+static uiBox *panel;
+static uiCheckbox *showExtents;
+static uiCheckbox *showLineBounds;
+static uiCheckbox *showLineGuides;
+
+// TODO should this be const?
+static double strokeDashes[] = { 5, 2 };
+// TODO this should be const
+static uiDrawStrokeParams strokeParams = {
+	.Cap = uiDrawLineCapFlat,
+	.Join = uiDrawLineJoinMiter,
+	.Thickness = 1,
+	.MiterLimit = uiDrawDefaultMiterLimit,
+	.Dashes = strokeDashes,
+	.NumDashes = 2,
+	.DashPhase = 0,
+};
+
+// TODO should be const?
+static uiDrawBrush fillBrushes[4] = {
+	{
+		.Type = uiDrawBrushTypeSolid,
+		.R = 1.0,
+		.G = 0.0,
+		.B = 0.0,
+		.A = 0.5,
+	},
+	{
+		.Type = uiDrawBrushTypeSolid,
+		.R = 0.0,
+		.G = 1.0,
+		.B = 0.0,
+		.A = 0.5,
+	},
+	{
+		.Type = uiDrawBrushTypeSolid,
+		.R = 0.0,
+		.G = 0.0,
+		.B = 1.0,
+		.A = 0.5,
+	},
+	{
+		.Type = uiDrawBrushTypeSolid,
+		.R = 0.0,
+		.G = 1.0,
+		.B = 1.0,
+		.A = 0.5,
+	},
+};
+// TODO come up with better colors
+static uiDrawBrush strokeBrushes[3] = {
+	// baseline
+	{
+		.Type = uiDrawBrushTypeSolid,
+		.R = 0.5,
+		.G = 0.5,
+		.B = 0.0,
+		.A = 0.75,
+	},
+	// ascent
+	{
+		.Type = uiDrawBrushTypeSolid,
+		.R = 1.0,
+		.G = 0.0,
+		.B = 1.0,
+		.A = 0.75,
+	},
+	// descent
+	{
+		.Type = uiDrawBrushTypeSolid,
+		.R = 0.5,
+		.G = 0.75,
+		.B = 1.0,
+		.A = 0.75,
+	},
+};
+
 static void draw(uiAreaDrawParams *p)
 {
 	uiDrawPath *path;
 	uiDrawTextLayout *layout;
+	uiDrawBrush b;
+
+	b.Type = uiDrawBrushTypeSolid;
+
+	// only clip the text, not the guides
+	uiDrawSave(p->Context);
 
 	path = uiDrawNewPath(uiDrawFillModeWinding);
 	uiDrawPathAddRectangle(path, margins, margins,
@@ -44,33 +127,131 @@ static void draw(uiAreaDrawParams *p)
 	uiDrawFreePath(path);
 
 	// TODO get rid of this later
+#if 0
 	path = uiDrawNewPath(uiDrawFillModeWinding);
 	uiDrawPathAddRectangle(path, -100, -100,
 		p->AreaWidth * 2,
 		p->AreaHeight * 2);
 	uiDrawPathEnd(path);
-	uiDrawBrush b;
-	b.Type = uiDrawBrushTypeSolid;
 	b.R = 0.0;
 	b.G = 1.0;
 	b.B = 0.0;
 	b.A = 1.0;
 	uiDrawFill(p->Context, path, &b);
 	uiDrawFreePath(path);
+#endif
 
 	layout = uiDrawNewTextLayout(attrstr,
 		&defaultFont,
 		p->AreaWidth - 2 * margins);
 	uiDrawText(p->Context, layout, margins, margins);
+
+	uiDrawRestore(p->Context);
+
+	if (uiCheckboxChecked(showExtents)) {
+		double width, height;
+
+		uiDrawTextLayoutExtents(layout, &width, &height);
+		path = uiDrawNewPath(uiDrawFillModeWinding);
+		uiDrawPathAddRectangle(path, margins, margins,
+			width, height);
+		uiDrawPathEnd(path);
+		b.R = 1.0;
+		b.G = 0.0;
+		b.B = 1.0;
+		b.A = 0.5;
+		uiDrawStroke(p->Context, path, &b, &strokeParams);
+		uiDrawFreePath(path);
+	}
+
+	if (uiCheckboxChecked(showLineBounds) || uiCheckboxChecked(showLineGuides)) {
+		uiDrawTextLayoutLineMetrics m;
+		int i, n;
+		int fill = 0;
+
+		n = uiDrawTextLayoutNumLines(layout);
+		for (i = 0; i < n; i++) {
+			uiDrawTextLayoutLineGetMetrics(layout, i, &m);
+
+			if (uiCheckboxChecked(showLineBounds)) {
+				path = uiDrawNewPath(uiDrawFillModeWinding);
+				uiDrawPathAddRectangle(path, margins + m.X, margins + m.Y,
+					m.Width, m.Height);
+				uiDrawPathEnd(path);
+				uiDrawFill(p->Context, path, fillBrushes + fill);
+				uiDrawFreePath(path);
+				fill = (fill + 1) % 4;
+			}
+			if (uiCheckboxChecked(showLineGuides)) {
+				// baseline
+				path = uiDrawNewPath(uiDrawFillModeWinding);
+				uiDrawPathNewFigure(path,
+					margins + m.X,
+					margins + m.BaselineY);
+				uiDrawPathLineTo(path,
+					margins + m.X + m.Width,
+					margins + m.BaselineY);
+				uiDrawPathEnd(path);
+				uiDrawStroke(p->Context, path, &(strokeBrushes[0]), &strokeParams);
+				uiDrawFreePath(path);
+
+				// ascent line
+				path = uiDrawNewPath(uiDrawFillModeWinding);
+				uiDrawPathNewFigure(path,
+					margins + m.X,
+					margins + m.BaselineY - m.Ascent);
+				uiDrawPathLineTo(path,
+					margins + m.X + m.Width,
+					margins + m.BaselineY - m.Ascent);
+				uiDrawPathEnd(path);
+				uiDrawStroke(p->Context, path, &(strokeBrushes[1]), &strokeParams);
+				uiDrawFreePath(path);
+
+				// descent line
+				path = uiDrawNewPath(uiDrawFillModeWinding);
+				uiDrawPathNewFigure(path,
+					margins + m.X,
+					margins + m.BaselineY + m.Descent);
+				uiDrawPathLineTo(path,
+					margins + m.X + m.Width,
+					margins + m.BaselineY + m.Descent);
+				uiDrawPathEnd(path);
+				uiDrawStroke(p->Context, path, &(strokeBrushes[2]), &strokeParams);
+				uiDrawFreePath(path);
+			}
+		}
+	}
+
 	uiDrawFreeTextLayout(layout);
 }
 
 static struct example basicExample;
 
+// TODO share?
+static void checkboxChecked(uiCheckbox *c, void *data)
+{
+	redraw();
+}
+
+static uiCheckbox *newCheckbox(const char *text)
+{
+	uiCheckbox *c;
+
+	c = uiNewCheckbox(text);
+	uiCheckboxOnToggled(c, checkboxChecked, NULL);
+	uiBoxAppend(panel, uiControl(c), 0);
+	return c;
+}
+
 struct example *mkBasicExample(void)
 {
+	panel = uiNewVerticalBox();
+	showExtents = newCheckbox("Show Layout Extents");
+	showLineBounds = newCheckbox("Show Line Bounds");
+	showLineGuides = newCheckbox("Show Line Guides");
+
 	basicExample.name = "Basic Paragraph of Text";
-	basicExample.panel = uiControl(uiNewVerticalBox());
+	basicExample.panel = uiControl(panel);
 	basicExample.draw = draw;
 
 	attrstr = uiNewAttributedString(text);

unix/drawtext.c

@@ -4,6 +4,7 @@
 
 struct uiDrawTextLayout {
 	PangoLayout *layout;
+	uiDrawTextLayoutLineMetrics *lineMetrics;
 };
 
 // See https://developer.gnome.org/pango/1.30/pango-Cairo-Rendering.html#pango-Cairo-Rendering.description
@@ -35,6 +36,55 @@ static const PangoStretch pangoStretches[] = {
 	[uiDrawTextStretchUltraExpanded] = PANGO_STRETCH_ULTRA_EXPANDED,
 };
 
+// TODO neither these nor the overall extents seem to include trailing whitespace... we need to figure that out too
+static void computeLineMetrics(uiDrawTextLayout *tl)
+{
+	PangoLayoutIter *iter;
+	PangoLayoutLine *pll;
+	PangoRectangle lineStartPos, lineExtents;
+	int i, n;
+	uiDrawTextLayoutLineMetrics *m;
+
+	n = pango_layout_get_line_count(tl->layout);
+	tl->lineMetrics = (uiDrawTextLayoutLineMetrics *) uiAlloc(n * sizeof (uiDrawTextLayoutLineMetrics), "uiDrawTextLayoutLineMetrics[] (text layout)");
+	iter = pango_layout_get_iter(tl->layout);
+
+	m = tl->lineMetrics;
+	for (i = 0; i < n; i++) {
+		int baselineY;
+
+		// TODO we use this instead of _get_yrange() because of the block of text in that function's description about how line spacing is distributed in Pango; we have to worry about this when we start adding line spacing...
+		baselineY = pango_layout_iter_get_baseline(iter);
+		pll = pango_layout_iter_get_line_readonly(iter);
+		pango_layout_index_to_pos(tl->layout, pll->start_index, &lineStartPos);
+		pango_layout_line_get_extents(pll, NULL, &lineExtents);
+		// TODO unref pll?
+
+		// TODO is this correct for RTL glyphs?
+		m->X = pangoToCairo(lineStartPos.x);
+		// TODO fix the whole combined not being updated shenanigans in the static build (here because ugh)
+		m->Y = pangoToCairo(baselineY - PANGO_ASCENT(lineExtents));
+		m->Width = pangoToCairo(lineExtents.width);
+		m->Height = pangoToCairo(lineExtents.height);
+
+		m->BaselineY = pangoToCairo(baselineY);
+		m->Ascent = pangoToCairo(PANGO_ASCENT(lineExtents));
+		m->Descent = pangoToCairo(PANGO_DESCENT(lineExtents));
+		m->Leading = 0;		// TODO
+
+		m->ParagraphSpacingBefore = 0;		// TODO
+		m->LineHeightSpace = 0;				// TODO
+		m->LineSpacing = 0;				// TODO
+		m->ParagraphSpacing = 0;			// TODO
+
+		// don't worry about the return value; we're not using this after the last line
+		pango_layout_iter_next_line(iter);
+		m++;
+	}
+
+	pango_layout_iter_free(iter);
+}
+
 uiDrawTextLayout *uiDrawNewTextLayout(uiAttributedString *s, uiDrawFontDescriptor *defaultFont, double width)
 {
 	uiDrawTextLayout *tl;
@@ -76,11 +126,14 @@ uiDrawTextLayout *uiDrawNewTextLayout(uiAttributedString *s, uiDrawFontDescripto
 
 	// TODO attributes
 
+	computeLineMetrics(tl);
+
 	return tl;
 }
 
 void uiDrawFreeTextLayout(uiDrawTextLayout *tl)
 {
+	uiFree(tl->lineMetrics);
 	g_object_unref(tl->layout);
 	uiFree(tl);
 }
@@ -112,15 +165,12 @@ void uiDrawTextLayoutLineByteRange(uiDrawTextLayout *tl, int line, size_t *start
 	pll = pango_layout_get_line_readonly(tl->layout, line);
 	*start = pll->start_index;
 	*end = pll->start_index + pll->length;
-	// TODO unref?
+	// TODO unref pll?
 }
 
 void uiDrawTextLayoutLineGetMetrics(uiDrawTextLayout *tl, int line, uiDrawTextLayoutLineMetrics *m)
 {
-	PangoLayoutLine *pll;
+	*m = tl->lineMetrics[line];
-
-	pll = pango_layout_get_line_readonly(tl->layout, line);
-	// TODO unref?
 }
 
 // TODO