netsurf/desktop/scrollbar.c

/*
 * Copyright 2004-2008 James Bursa <bursa@users.sourceforge.net>
 * Copyright 2008 Michael Drake <tlsa@netsurf-browser.org>
 * Copyright 2009 Paul Blokus <paul_pl@users.sourceforge.net>
 *
 * This file is part of NetSurf, http://www.netsurf-browser.org/
 *
 * NetSurf is free software; you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation; version 2 of the License.
 *
 * NetSurf is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program.  If not, see <http://www.gnu.org/licenses/>.
 */

/** \file
 * Scrollbar widget (implementation).
 */

#include <stdbool.h>
#include <stdlib.h>

#include "desktop/mouse.h"
#include "desktop/scrollbar.h"
#include "desktop/options.h"
#include "desktop/plotters.h"
#include "desktop/plot_style.h"
#include "utils/log.h"
#include "utils/messages.h"
#include "utils/utils.h"


struct scrollbar {
	bool horizontal;	/* Horizontal scrollbar if true, else vertical
				 */
	int length;		/* Length of the scrollbar widget */

	int full_size;		/* Length of the full scrollable area */
	int visible_size;	/* Length visible part of the scrollable area */

	int offset;		/* Current scroll offset to visible area */

	int bar_pos;		/* Position of the scrollbar */
	int bar_len;		/* Length of the scrollbar */

	scrollbar_client_callback client_callback;	/* Callback receiving
							 * scrollbar events */
	void *client_data;	/* User data passed to the callback */

	bool dragging;		/* Flag indicating drag at progess */
	int drag_start_coord;	/* Coordinate value at drag start */
	int drag_start_pos;	/* Scrollbar offset or bar_pos at drag start */
	bool drag_content;	/* Flag indicating that the drag corresponds to
				 * a dragged content area, rather than a dragged
				 * scrollbar. */

	struct scrollbar *pair;	/* Parpendicular scrollbar, or NULL */
	bool pair_drag;		/* Flag indicating that the current drag affects
				   the perpendicular scrollbar too */
};



/*
 * Exported function.  Documented in scrollbar.h
 */
bool scrollbar_create(bool horizontal, int length, int full_size,
		int visible_size, void *client_data,
		scrollbar_client_callback client_callback,
		struct scrollbar **s)
{
	struct scrollbar *scrollbar;
	int well_length;

	scrollbar = malloc(sizeof(struct scrollbar));
	if (scrollbar == NULL) {
		LOG(("malloc failed"));
		warn_user("NoMemory", 0);
		*s = NULL;
		return false;
	}

	scrollbar->horizontal = horizontal;
	scrollbar->length = length;
	scrollbar->full_size = full_size;
	scrollbar->visible_size = visible_size;
	scrollbar->offset = 0;
	scrollbar->bar_pos = 0;
	scrollbar->pair = NULL;
	scrollbar->pair_drag = false;

	well_length = length - 2 * SCROLLBAR_WIDTH;
	scrollbar->bar_len = (full_size == 0) ? 0 :
			((well_length * visible_size) / full_size);

	scrollbar->client_callback = client_callback;
	scrollbar->client_data = client_data;

	scrollbar->dragging = false;
	scrollbar->drag_content = false;

	*s = scrollbar;

	return true;
}


/*
 * Exported function.  Documented in scrollbar.h
 */
void scrollbar_destroy(struct scrollbar *s)
{
	if (s->pair != NULL)
		s->pair->pair = NULL;
	free(s);
}


/**
 * Draw an outline rectangle common to a several scrollbar elements.
 *
 * \param x0	left border of the outline
 * \param y0	top border of the outline
 * \param x1	right border of the outline
 * \param y1	bottom border of the outline
 * \param c	base colour of the outline, the other colours are created by
 * 		lightening or darkening this one
 * \param ctx	current redraw context
 * \param inset true for inset outline, false for an outset one
 * \return
 */

static inline bool scrollbar_redraw_scrollbar_rectangle(int x0, int y0,
		int x1, int y1, colour c, bool inset,
		const struct redraw_context *ctx)
{
	const struct plotter_table *plot = ctx->plot;

	static plot_style_t c0 = {
		.stroke_type = PLOT_OP_TYPE_SOLID,
		.stroke_width = 1,
	};

	static plot_style_t c1 = {
		.stroke_type = PLOT_OP_TYPE_SOLID,
		.stroke_width = 1,
	};

	static plot_style_t c2 = {
		.stroke_type = PLOT_OP_TYPE_SOLID,
		.stroke_width = 1,
	};

	if (inset) {
		c0.stroke_colour = darken_colour(c);
		c1.stroke_colour = lighten_colour(c);
	} else {
		c0.stroke_colour = lighten_colour(c);
		c1.stroke_colour = darken_colour(c);
	}
	c2.stroke_colour = blend_colour(c0.stroke_colour, c1.stroke_colour);

	/* Plot the outline */
	if (!plot->line(x0, y0, x1, y0, &c0)) return false;
	if (!plot->line(x1, y0, x1, y1 + 1, &c1)) return false;
	if (!plot->line(x1, y0, x1, y0 + 1, &c2)) return false;
	if (!plot->line(x1, y1, x0, y1, &c1)) return false;
	if (!plot->line(x0, y1, x0, y0, &c0)) return false;
	if (!plot->line(x0, y1, x0, y1 + 1, &c2)) return false;

	return true;
}


/*
 * Exported function.  Documented in scrollbar.h
 */
bool scrollbar_redraw(struct scrollbar *s, int x, int y, 
		const struct rect *clip, float scale,
		const struct redraw_context *ctx)
{
	const struct plotter_table *plot = ctx->plot;
	int w = SCROLLBAR_WIDTH;
	int bar_pos, bar_c0, bar_c1;
	int v[6]; /* array of triangle vertices */
	int x0, y0, x1, y1;

	colour bg_fill_colour = gui_system_colour_char("Scrollbar");
	colour fg_fill_colour = gui_system_colour_char("ButtonFace");
	colour arrow_fill_colour = gui_system_colour_char("ButtonText");

	plot_style_t bg_fill_style = {
		.fill_type = PLOT_OP_TYPE_SOLID,
		.fill_colour = bg_fill_colour
	};
	plot_style_t fg_fill_style = {
		.fill_type = PLOT_OP_TYPE_SOLID,
		.fill_colour = fg_fill_colour
	};
	plot_style_t arrow_fill_style = {
		.fill_type = PLOT_OP_TYPE_SOLID,
		.fill_colour = arrow_fill_colour
	};

	x0 = x;
	y0 = y;
	x1 = x + (s->horizontal ? s->length : SCROLLBAR_WIDTH) - 1;
	y1 = y + (s->horizontal ? SCROLLBAR_WIDTH : s->length) - 1;
	bar_pos = s->bar_pos;
	bar_c1 = (s->horizontal ? x0 : y0) + SCROLLBAR_WIDTH +
			s->bar_pos + s->bar_len - 1;

	if (scale != 1.0) {
		w *= scale;
		x0 *= scale;
		y0 *= scale;
		x1 *= scale;
		y1 *= scale;
		bar_pos *= scale;
		bar_c1 *= scale;
	}

	bar_c0 = (s->horizontal ? x0 : y0) + w + bar_pos;

	if (x1 < clip->x0 || y1 < clip->y0 || clip->x1 < x0 || clip->y1 < y0)
		/* scrollbar is outside the clipping rectangle, nothing to
		 * render */
		return true;

	
	if (s->horizontal) {
		/* scrollbar is horizontal */
		
		/* scrollbar outline */
		if (!scrollbar_redraw_scrollbar_rectangle(x0, y0, x1, y1,
				bg_fill_colour, true, ctx))
			return false;
		/* left arrow icon border */
		if (!scrollbar_redraw_scrollbar_rectangle(x0 + 1,
		     		y0 + 1,
				x0 + w - 2,
    				y1 - 1,
				fg_fill_colour, false, ctx))
			return false;
		/* left arrow icon background */
		if (!plot->rectangle(x0 + 2,
		     		y0 + 2,
				x0 + w - 2,
    				y1 - 1,
				&fg_fill_style))
			return false;
		/* left arrow */
		v[0] = x0 + w / 4;
		v[1] = y0 + w / 2;
		v[2] = x0 + w * 3 / 4;
		v[3] = y0 + w / 4;
		v[4] = x0 + w * 3 / 4;
		v[5] = y0 + w * 3 / 4;
		if (!plot->polygon(v, 3, &arrow_fill_style))
			return false;
		/* scrollbar well background */
		if (!plot->rectangle(x0 + w - 1,
		     		y0 + 1,
	 			x1 - w + 2,
    				y1,
				&bg_fill_style))
			return false;
		/* scrollbar position indicator bar */
		if (!scrollbar_redraw_scrollbar_rectangle(bar_c0,
				y0 + 1,
				bar_c1,
				y1 - 1,
				fg_fill_colour, false, ctx))
			return false;
		if (!plot->rectangle(bar_c0 + 1,
		     		y0 + 2,
				bar_c1,
    				y1 - 1,
				&fg_fill_style))
			return false;
		/* right arrow icon border */
		if (!scrollbar_redraw_scrollbar_rectangle(x1 - w + 2,
				y0 + 1,
				x1 - 1,
				y1 - 1,
				fg_fill_colour, false, ctx))
			return false;
		/* right arrow icon background */
		if (!plot->rectangle(x1 - w + 3,
		     		y0 + 2,
				x1 - 1,
    				y1 - 1,
				&fg_fill_style))
			return false;
		/* right arrow */
		v[0] = x1 - w / 4 + 1;
		v[1] = y0 + w / 2;
		v[2] = x1 - w * 3 / 4 + 1;
		v[3] = y0 + w / 4;
		v[4] = x1 - w * 3 / 4 + 1;
		v[5] = y0 + w * 3 / 4;
		if (!plot->polygon(v, 3, &arrow_fill_style))
			return false;
	} else {
		/* scrollbar is vertical */
		
		/* outline */
		if (!scrollbar_redraw_scrollbar_rectangle(x0, y0, x1, y1,
				bg_fill_colour, true, ctx))
			return false;
 		/* top arrow background */
		if (!scrollbar_redraw_scrollbar_rectangle(x0 + 1,
				y0 + 1,
				x1 - 1,
				y0 + w - 2,
				fg_fill_colour, false, ctx))
			return false;
		if (!plot->rectangle(x0 + 2,
				y0 + 2,
				x1 - 1,
				y0 + w - 2,
				&fg_fill_style))
			return false;
		/* up arrow */
		v[0] = x0 + w / 2;
		v[1] = y0 + w / 4;
		v[2] = x0 + w / 4;
		v[3] = y0 + w * 3 / 4;
		v[4] = x0 + w * 3 / 4;
		v[5] = y0 + w * 3 / 4;
		if (!plot->polygon(v, 3, &arrow_fill_style))
			return false;
		/* scrollbar well background */
		if (!plot->rectangle(x0 + 1,
				y0 + w - 1,
				x1,
				y1 - w + 2,
				&bg_fill_style))
			return false;
		/* scrollbar position indicator bar */
		if (!scrollbar_redraw_scrollbar_rectangle(x0 + 1,
				bar_c0,
				x1 - 1,
				bar_c1,
				fg_fill_colour, false, ctx))
			return false;
		if (!plot->rectangle(x0 + 2,
				bar_c0 + 1,
				x1 - 1,
				bar_c1,
				&fg_fill_style))
			return false;
		/* bottom arrow background */
		if (!scrollbar_redraw_scrollbar_rectangle(x0 + 1,
				y1 - w + 2,
				x1 - 1,
				y1 - 1,
				fg_fill_colour, false, ctx))
			return false;
		if (!plot->rectangle(x0 + 2,
				y1 - w + 3,
				x1 - 1,
				y1 - 1,
				&fg_fill_style))
			return false;
		/* down arrow */
		v[0] = x0 + w / 2;
		v[1] = y1 - w / 4 + 1;
		v[2] = x0 + w / 4;
		v[3] = y1 - w * 3 / 4 + 1;
		v[4] = x0 + w * 3 / 4;
		v[5] = y1 - w * 3 / 4 + 1;
		if (!plot->polygon(v, 3, &arrow_fill_style))
			return false;
	}

	return true;
}


/*
 * Exported function.  Documented in scrollbar.h
 */
void scrollbar_set(struct scrollbar *s, int value, bool bar_pos)
{
	int well_length;
	int old_offset = s->offset;
	struct scrollbar_msg_data msg;

	if (value < 0)
		value = 0;

	if (s->full_size == s->visible_size)
		return;

	well_length = s->length - 2 * SCROLLBAR_WIDTH;
	if (bar_pos) {
		if (value > well_length - s->bar_len)
			s->bar_pos = well_length - s->bar_len;
		else
			s->bar_pos = value;

		s->offset = ((well_length - s->bar_len) < 1) ? 0 :
				(((s->full_size - s->visible_size) *
				s->bar_pos) / (well_length - s->bar_len));

	} else {
		if (value > s->full_size - s->visible_size)
			s->offset = s->full_size - s->visible_size;
		else
			s->offset = value;

		s->bar_pos = (s->full_size < 1) ? 0 :
				((well_length * s->offset) / s->full_size);
	}

	if (s->offset == old_offset)
		/* Nothing happened */
		return;

	msg.scrollbar = s;
	msg.msg = SCROLLBAR_MSG_MOVED;
	msg.scroll_offset = s->offset;
	s->client_callback(s->client_data, &msg);

	msg.msg = SCROLLBAR_MSG_REDRAW;
	msg.x0 = s->horizontal ? SCROLLBAR_WIDTH - 1 : 0;
	msg.y0 = s->horizontal ? 0 : SCROLLBAR_WIDTH - 1;
	msg.x1 = (s->horizontal ? s->length - SCROLLBAR_WIDTH + 1 :
			SCROLLBAR_WIDTH);
	msg.y1 = (s->horizontal ? SCROLLBAR_WIDTH :
			s->length - SCROLLBAR_WIDTH + 1);

	s->client_callback(s->client_data, &msg);
}


/*
 * Exported function.  Documented in scrollbar.h
 */
bool scrollbar_scroll(struct scrollbar *s, int change)
{
	int well_length;
	int old_offset = s->offset;
	struct scrollbar_msg_data msg;

	if (change == 0 || s->full_size <= s->visible_size)
		/* zero scroll step, or unscrollable */
		return false;

	/* Convert named change values to appropriate pixel offset value */
	switch (change) {
	case SCROLL_TOP:
		change = -s->full_size;
		break;

	case SCROLL_PAGE_UP:
		change = -s->visible_size;
		break;

	case SCROLL_PAGE_DOWN:
		change = s->visible_size;
		break;

	case SCROLL_BOTTOM:
		change = s->full_size;
		break;

	default:
		/* Change value is already a pixel offset */
		break;
	}

	/* Get new offset */
	if (s->offset + change > s->full_size - s->visible_size)
		s->offset = s->full_size - s->visible_size;
	else if (s->offset + change < 0)
		s->offset = 0;
	else
		s->offset += change;

	if (s->offset == old_offset)
		/* Nothing happened */
		return false;

	/* Update scrollbar */
	well_length = s->length - 2 * SCROLLBAR_WIDTH;
	s->bar_pos = (s->full_size < 1) ? 0 :
			((well_length * s->offset) / s->full_size);

	msg.scrollbar = s;
	msg.msg = SCROLLBAR_MSG_MOVED;
	msg.scroll_offset = s->offset;
	s->client_callback(s->client_data, &msg);

	msg.msg = SCROLLBAR_MSG_REDRAW;
	msg.x0 = s->horizontal ? SCROLLBAR_WIDTH - 1 : 0;
	msg.y0 = s->horizontal ? 0 : SCROLLBAR_WIDTH - 1;
	msg.x1 = (s->horizontal ? s->length - SCROLLBAR_WIDTH + 1 :
			SCROLLBAR_WIDTH);
	msg.y1 = (s->horizontal ? SCROLLBAR_WIDTH :
			s->length - SCROLLBAR_WIDTH + 1);

	s->client_callback(s->client_data, &msg);

	return true;
}


/*
 * Exported function.  Documented in scrollbar.h
 */
int scrollbar_get_offset(struct scrollbar *s)
{
	if (s == NULL)
		return 0;
	return s->offset;
}


/*
 * Exported function.  Documented in scrollbar.h
 */
void scrollbar_set_extents(struct scrollbar *s, int length,
		int visible_size, int full_size)
{
	int well_length;
	int cur_excess = s->full_size - s->visible_size;

	if (length != -1)
		s->length = length;
	if (visible_size != -1)
		s->visible_size = visible_size;
	if (full_size != -1)
		s->full_size = full_size;

	if (s->full_size < s->visible_size)
		s->full_size = s->visible_size;

	/* Update scroll offset (scaled in proportion with change in excess) */
	s->offset = (cur_excess < 1) ? 0 :
			((s->full_size - s->visible_size) * s->offset /
			cur_excess);

	well_length = s->length - 2 * SCROLLBAR_WIDTH;

	if (s->full_size < 1) {
		s->bar_len = well_length;
		s->bar_pos = 0;
	} else {
		s->bar_len = (well_length * s->visible_size) / s->full_size;
		s->bar_pos = (well_length * s->offset) / s->full_size;
	}
}


/*
 * Exported function.  Documented in scrollbar.h
 */
bool scrollbar_is_horizontal(struct scrollbar *s)
{
	return s->horizontal;
}


/**
 * Internal procedure used for starting a drag scroll for a scrollbar.
 *
 * \param s		the scrollbar to start the drag for
 * \param x		the X coordinate of the drag start
 * \param y		the Y coordinate of the drag start
 * \param content_drag	whether this should be a reverse drag (used when the
 * 			user drags the content area, rather than the scrollbar)
 * \param pair		whether the drag is a '2D' scroll
 */

static void scrollbar_drag_start_internal(struct scrollbar *s, int x, int y,
		bool content_drag, bool pair)
{
	struct scrollbar_msg_data msg;

	s->drag_start_coord = s->horizontal ? x : y;
	s->drag_start_pos = (content_drag) ? s->offset : s->bar_pos;

	s->dragging = true;
	s->drag_content = content_drag;

	msg.scrollbar = s;

	/* \todo - some proper numbers please! */
	if (s->horizontal) {
		msg.x0 = -2048;
		msg.x1 = 2048;
		msg.y0 = 0;
		msg.y1 = 0;
	} else {
		msg.x0 = 0;
		msg.x1 = 0;
		msg.y0 = -2048;
		msg.y1 = 2048;
	}

	if (pair && s->pair != NULL) {
		s->pair_drag = true;

		s->pair->drag_start_coord =
				s->pair->horizontal ? x : y;

		s->pair->drag_start_pos = (content_drag) ? s->pair->offset :
				s->pair->bar_pos;

		s->pair->dragging = true;
		s->pair->drag_content = content_drag;

		if (s->pair->horizontal) {
			msg.x0 = -2048;
			msg.x1 = 2048;
		} else {
			msg.y0 = -2048;
			msg.y1 = 2048;
		}
	}
	msg.msg = SCROLLBAR_MSG_SCROLL_START;
	s->client_callback(s->client_data, &msg);
}


/*
 * Exported function.  Documented in scrollbar.h
 */
const char *scrollbar_mouse_action(struct scrollbar *s,
		browser_mouse_state mouse, int x, int y)
{
	int x0, y0, x1, y1;
	int val;
	const char *status;
	bool h;

	/* we want mouse presses and mouse drags that were not started at the
	 * scrollbar indication bar to be launching actions on the scroll area
	 */
	bool but1 = ((mouse & BROWSER_MOUSE_PRESS_1) ||
			((mouse & BROWSER_MOUSE_HOLDING_1) &&
			(mouse & BROWSER_MOUSE_DRAG_ON) &&
			!s->dragging));
	bool but2 = ((mouse & BROWSER_MOUSE_PRESS_2) ||
			((mouse & BROWSER_MOUSE_HOLDING_2) &&
			(mouse & BROWSER_MOUSE_DRAG_ON) &&
			!s->dragging));

	h = s->horizontal;

	x0 = 0;
	y0 = 0;
	x1 = h ? s->length : SCROLLBAR_WIDTH;
	y1 = h ? SCROLLBAR_WIDTH : s->length;

	if (!s->dragging && !(x >= x0 && x <= x1 && y >= y0 && y <= y1)) {
		/* Not a drag and mouse outside scrollbar widget */
		return NULL;
	}


	if (h)
		val = x;
	else
		val = y;

	if (s->dragging) {
		val -= s->drag_start_coord;
		if (s->drag_content)
			val = -val;
		if (val != 0)
			scrollbar_set(s, s->drag_start_pos + val,
					!(s->drag_content));
		if (s->pair_drag) {
			scrollbar_mouse_action(s->pair, mouse, x, y);
			status = messages_get("ScrollBoth");
		} else
			status = messages_get(h ? "ScrollH" : "ScrollV");

		return status;
	}

	if (val < SCROLLBAR_WIDTH) {
		/* left/up arrow */
		
		status = messages_get(h ? "ScrollLeft" : "ScrollUp");
		if (but1)
			scrollbar_set(s, s->offset - SCROLLBAR_WIDTH, false);
		else if (but2)
			scrollbar_set(s, s->offset + SCROLLBAR_WIDTH, false);

	} else if (val < SCROLLBAR_WIDTH + s->bar_pos) {
		/* well between left/up arrow and bar */

		status = messages_get(h ? "ScrollPLeft" : "ScrollPUp");

		if (but1)
			scrollbar_set(s, s->offset - s->length, false);
		else if (but2)
			scrollbar_set(s, s->offset + s->length, false);

	} else if (val > s->length - SCROLLBAR_WIDTH) {
		/* right/down arrow */

		status = messages_get(h ? "ScrollRight" : "ScrollDown");

		if (but1)
			scrollbar_set(s, s->offset + SCROLLBAR_WIDTH, false);
		else if (but2)
			scrollbar_set(s, s->offset - SCROLLBAR_WIDTH, false);

	} else if (val > SCROLLBAR_WIDTH + s->bar_pos +
			s->bar_len) {
		/* well between right/down arrow and bar */

		status = messages_get(h ? "ScrollPRight" : "ScrollPDown");
		if (but1)
			scrollbar_set(s, s->offset + s->length, false);
		else if (but2)
			scrollbar_set(s, s->offset - s->length, false);
	}
	else {
		/* scrollbar position indication bar */
		
		status = messages_get(h ? "ScrollH" : "ScrollV");
	}

	
	if (mouse & (BROWSER_MOUSE_DRAG_1 | BROWSER_MOUSE_DRAG_2) &&
		   	(val >= SCROLLBAR_WIDTH + s->bar_pos
		   	&& val < SCROLLBAR_WIDTH + s->bar_pos +
		   			s->bar_len))
		/* The mouse event is a drag start on the scrollbar position
		 * indication bar. */
		scrollbar_drag_start_internal(s, x, y, false,
				(mouse & BROWSER_MOUSE_DRAG_2) ? true : false);

	return status;
}


/*
 * Exported function.  Documented in scrollbar.h
 */
void scrollbar_mouse_drag_end(struct scrollbar *s,
		browser_mouse_state mouse, int x, int y)
{
	struct scrollbar_msg_data msg;
	int val, drag_start_pos;

	assert(s->dragging);

	drag_start_pos = s->drag_start_pos;
	val = (s->horizontal ? x : y) - s->drag_start_coord;

	if (s->drag_content)
		val = -val;
	if (val != 0)
		scrollbar_set(s, drag_start_pos + val, !(s->drag_content));

	s->dragging = false;
	s->drag_content = false;

	if (s->pair_drag) {
		s->pair_drag = false;

		drag_start_pos = s->pair->drag_start_pos;
		val = (s->pair->horizontal ? x : y) - s->pair->drag_start_coord;

		if (s->pair->drag_content)
			val = -val;
		if (val != 0)
			scrollbar_set(s->pair, drag_start_pos + val,
					!(s->pair->drag_content));

		s->pair->dragging = false;
		s->pair->drag_content = false;
	}

	msg.scrollbar = s;
	msg.msg = SCROLLBAR_MSG_SCROLL_FINISHED;
	s->client_callback(s->client_data, &msg);
}


/*
 * Exported function.  Documented in scrollbar.h
 */
void scrollbar_start_content_drag(struct scrollbar *s, int x, int y)
{
	scrollbar_drag_start_internal(s, x, y, true, true);
}


/*
 * Exported function.  Documented in scrollbar.h
 */
void scrollbar_make_pair(struct scrollbar *horizontal,
		struct scrollbar *vertical)
{
	assert(horizontal->horizontal &&
			!vertical->horizontal);

	horizontal->pair = vertical;
	vertical->pair = horizontal;
}


/*
 * Exported function.  Documented in scrollbar.h
 */
void *scrollbar_get_data(struct scrollbar *s)
{
	return s->client_data;
}