Expanded the hittest example by handling keyboard input. I should probably rename it to The Caret and Graphemes.

examples/drawtext/basic.c

@@ -254,6 +254,7 @@ struct example *mkBasicExample(void)
 	basicExample.panel = uiControl(panel);
 	basicExample.draw = draw;
 	basicExample.mouse = NULL;
+	basicExample.key = NULL;
 
 	attrstr = uiNewAttributedString(text);
 

examples/drawtext/drawtext.h

@@ -8,6 +8,7 @@ struct example {
 	uiControl *panel;
 	void (*draw)(uiAreaDrawParams *p);
 	void (*mouse)(uiAreaMouseEvent *e);
+	int (*key)(uiAreaKeyEvent *e);
 	// TODO key?
 };
 

examples/drawtext/hittest.c

@@ -35,7 +35,6 @@ static uiCheckbox *showLineBounds;
 
 static int caretLine = -1;
 static size_t caretPos;
-//static double caretX;
 
 // TODO should be const?
 static uiDrawBrush fillBrushes[4] = {
@@ -136,6 +135,7 @@ static void mouse(uiAreaMouseEvent *e)
 		&caretPos, &caretLine);
 	uiDrawFreeTextLayout(layout);
 
+	// TODO move this into the draw handler so it is reflected by keyboard-based position changes
 	// urgh %zd is not supported by MSVC with sprintf()
 	// TODO get that part in test/ about having no other option
 	sprintf(labelText, "pos %d line %d",
@@ -145,6 +145,41 @@ static void mouse(uiAreaMouseEvent *e)
 	redraw();
 }
 
+static int key(uiAreaKeyEvent *e)
+{
+	size_t grapheme;
+
+	if (e->Up)
+		return 0;
+	if (e->Key != 0)
+		return 0;
+	switch (e->ExtKey) {
+	case uiExtKeyUp:
+		// TODO
+		return 1;
+	case uiExtKeyDown:
+		// TODO
+		return 1;
+	case uiExtKeyLeft:
+		grapheme = uiAttributedStringByteIndexToGrapheme(attrstr, caretPos);
+		if (grapheme == 0)
+			return 0;
+		grapheme--;
+		caretPos = uiAttributedStringGraphemeToByteIndex(attrstr, grapheme);
+		redraw();
+		return 1;
+	case uiExtKeyRight:
+		grapheme = uiAttributedStringByteIndexToGrapheme(attrstr, caretPos);
+		if (grapheme == uiAttributedStringNumGraphemes(attrstr))
+			return 0;
+		grapheme++;
+		caretPos = uiAttributedStringGraphemeToByteIndex(attrstr, grapheme);
+		redraw();
+		return 1;
+	}
+	return 0;
+}
+
 static struct example hitTestExample;
 
 // TODO share?
@@ -174,6 +209,7 @@ struct example *mkHitTestExample(void)
 	hitTestExample.panel = uiControl(panel);
 	hitTestExample.draw = draw;
 	hitTestExample.mouse = mouse;
+	hitTestExample.key = key;
 
 	attrstr = uiNewAttributedString(text);
 

examples/drawtext/main.c

@@ -47,7 +47,8 @@ static void handlerDragBroken(uiAreaHandler *ah, uiArea *a)
 
 static int handlerKeyEvent(uiAreaHandler *ah, uiArea *a, uiAreaKeyEvent *e)
 {
-	// reject all keys
+	if (examples[curExample]->key != NULL)
+		return examples[curExample]->key(e);
 	return 0;
 }