Function stb_text_locate_coord

KBotExt/imgui/imstb_textedit.h:396–453

traverse the layout to locate the nearest character to a display position

// traverse the layout to locate the nearest character to a display position
static int stb_text_locate_coord(STB_TEXTEDIT_STRING* str, float x, float y)
{
	StbTexteditRow r;
	int n = STB_TEXTEDIT_STRINGLEN(str);
	float base_y = 0, prev_x;
	int i = 0, k;

	r.x0 = r.x1 = 0;
	r.ymin = r.ymax = 0;
	r.num_chars = 0;

	// search rows to find one that straddles 'y'
	while (i < n) {
		STB_TEXTEDIT_LAYOUTROW(&r, str, i);
		if (r.num_chars <= 0)
			return n;

		if (i == 0 && y < base_y + r.ymin)
			return 0;

		if (y < base_y + r.ymax)
			break;

		i += r.num_chars;
		base_y += r.baseline_y_delta;
	}

	// below all text, return 'after' last character
	if (i >= n)
		return n;

	// check if it's before the beginning of the line
	if (x < r.x0)
		return i;

	// check if it's before the end of the line
	if (x < r.x1) {
		// search characters in row for one that straddles 'x'
		prev_x = r.x0;
		for (k = 0; k < r.num_chars; ++k) {
			float w = STB_TEXTEDIT_GETWIDTH(str, i, k);
			if (x < prev_x + w) {
				if (x < prev_x + w / 2)
					return k + i;
				else
					return k + i + 1;
			}
			prev_x += w;
		}
		// shouldn't happen, but if it does, fall through to end-of-line case
	}

	// if the last character is a newline, return that. otherwise return 'after' the last character
	if (STB_TEXTEDIT_GETCHAR(str, i + r.num_chars - 1) == STB_TEXTEDIT_NEWLINE)
		return i + r.num_chars - 1;
	else
		return i + r.num_chars;
}