/*
 * This file is part of NetSurf, http://netsurf.sourceforge.net/
 * Licensed under the GNU General Public License,
 *		  http://www.opensource.org/licenses/gpl-license
 * Copyright 2004, 2005 Richard Wilson <info@tinct.net>
 */

#include <stdbool.h>
#include <stdlib.h>
#include <string.h>
#include <swis.h>
#include "oslib/colourtrans.h"
#include "oslib/os.h"
#include "oslib/osspriteop.h"
#include "oslib/wimp.h"
#include "oslib/wimpreadsysinfo.h"
#include "netsurf/riscos/buffer.h"
#include "netsurf/riscos/options.h"
#include "netsurf/riscos/tinct.h"
#include "netsurf/riscos/wimp.h"
#include "netsurf/utils/log.h"
//#define NDEBUG
#define BUFFER_EXCLUSIVE_USER_REDRAW "Only support pure user redraw (faster)"
//#define BUFFER_EMULATE_32BPP "Redirect to a 32bpp sprite and plot with Tinct"

/*	SCREEN BUFFERING
	================

	Because RISC OS provides no native way for windows to be buffered (ie
	the contents is only updated when the task has finished doing any
	drawing) certain situation cause the window contents to flicker in an
	undesirable manner. Examples of this are GIF and MNG animations, and
	web pages with fixed backgrounds.

	To overcome this, a very simple, transparent, interface is provided here
	to allow for output to be buffered. It should be noted that screen
	buffering can lower the perceived client response time as the user is
	unable to see that the application is doing anything.

	[rjw] - Mon 19th July 2004
*/

static void ro_gui_buffer_free(void);


/** The buffer characteristics
*/
static osspriteop_area *buffer = NULL;
static char buffer_name[] = "scr_buffer\0\0";

/** The current clip area
*/
static os_box clipping;

/** The current save area
*/
static osspriteop_save_area *save_area;
static osspriteop_area *context1;
static osspriteop_id context2;
static osspriteop_save_area *context3;

/** The current sprite mode
*/
static os_mode mode;

/**
 * Opens a buffer for writing to.
 *
 * \param redraw the current WIMP redraw area to buffer
 */
void ro_gui_buffer_open(wimp_draw *redraw) {
	int size;
	int orig_x0, orig_y0;
	int total_size;
	os_coord sprite_size;
	int bpp, word_width;
	bool palette;
	os_error *error;
	int palette_size = 0;
#ifdef BUFFER_EXCLUSIVE_USER_REDRAW
	osspriteop_header *header;
#endif

	/*	Close any open buffer
	*/
	if (buffer)
		ro_gui_buffer_close();

	/*	Store our clipping region
	*/
	clipping = redraw->clip;

	/*	Work out how much buffer we need
	*/
	sprite_size.x = clipping.x1 - clipping.x0 + 1;
	sprite_size.y = clipping.y1 - clipping.y0 + 1;
	ro_convert_os_units_to_pixels(&sprite_size, (os_mode)-1);
	if (sprite_size.y == 1) /* work around SpriteExtend bug */
		sprite_size.y = 2;


#ifdef BUFFER_EMULATE_32BPP
	bpp = 5;
	palette = false;
#else
	/*	Get the screen depth as we can't use palettes for >8bpp
	*/
	xos_read_mode_variable((os_mode)-1, os_MODEVAR_LOG2_BPP, &bpp, 0);
	palette = (bpp < 4);
#endif

	/*	Get our required buffer size
	*/
	word_width = ((sprite_size.x << bpp) + 31) >> 5;
	if (palette)
		palette_size = ((1 << (1 << bpp)) << 3);
	total_size = sizeof(osspriteop_area) + sizeof(osspriteop_header) +
			(word_width * sprite_size.y * 4) + palette_size;
	buffer = (osspriteop_area *)malloc(total_size);
	if (!buffer) {
		LOG(("Failed to allocate memory"));
		return;
	}
	buffer->size = total_size;
	buffer->first = 16;

#ifdef BUFFER_EMULATE_32BPP
	mode = tinct_SPRITE_MODE;
#else
	if (bpp == 32) {
		mode = tinct_SPRITE_MODE;
	} else {
		if ((error = xwimpreadsysinfo_wimp_mode(&mode)) != NULL) {
			LOG(("Error reading mode '%s'", error->errmess));
			ro_gui_buffer_free();
			return;
		}
	}
#endif

#ifdef BUFFER_EXCLUSIVE_USER_REDRAW
	/*	Create the sprite manually so we don't waste time clearing the
		background.
	*/
	buffer->sprite_count = 1;
	buffer->used = total_size;
	header = (osspriteop_header *)(buffer + 1);
	header->size = total_size - sizeof(osspriteop_area);
	memcpy(header->name, buffer_name, 12);
	header->width = word_width - 1;
	header->height = sprite_size.y - 1;
	header->left_bit = 0;
	header->right_bit = ((sprite_size.x << bpp) - 1) & 31;
	header->image = sizeof(osspriteop_header) + palette_size;
	header->mask = header->image;
	header->mode = mode;
	if (palette)
		xcolourtrans_read_palette((osspriteop_area *)mode,
			(osspriteop_id)colourtrans_CURRENT_MODE,
			(os_palette *)(header + 1), palette_size,
			(colourtrans_palette_flags)
				colourtrans_FLASHING_PALETTE, 0);
#else
	/*	Read the current contents of the screen
	*/
	buffer->sprite_count = 0;
	buffer->used = 16;
	if ((error = xosspriteop_get_sprite_user_coords(osspriteop_NAME,
			buffer, buffer_name, palette,
			clipping.x0, clipping.y0,
			clipping.x1, clipping.y1)) != NULL) {
		LOG(("Grab error '%s'", error->errmess));
		ro_gui_buffer_free();
		return;
	}
#endif
	/*	Allocate OS_SpriteOp save area
	*/
	if ((error = xosspriteop_read_save_area_size(osspriteop_PTR,
			buffer, (osspriteop_id)(buffer + 1), &size)) != NULL) {
		LOG(("Save area error '%s'", error->errmess));
		ro_gui_buffer_free();
		return;
	}
	if ((save_area = malloc((size_t)size)) == NULL) {
		ro_gui_buffer_free();
		return;
	}
	save_area->a[0] = 0;

	/*	Switch output to sprite
	*/
	if ((error = xosspriteop_switch_output_to_sprite(osspriteop_PTR,
			buffer, (osspriteop_id)(buffer + 1), save_area, 0,
			(int *)&context1, (int *)&context2,
			(int *)&context3)) != NULL) {
		LOG(("Switching error '%s'", error->errmess));
		free(save_area);
		ro_gui_buffer_free();
		return;
	}

	/*	Move the origin such that (x0, y0) becomes (0, 0). To do this
		we use VDU 29,(1 << 16) - x0; (1 << 16) - y0; because RISC OS
		is so insanely legacy driven.
	*/
	orig_x0 = (1 << 16) - clipping.x0;
	orig_y0 = (1 << 16) - clipping.y0;
	os_writec((char)29);
	os_writec(orig_x0 & 0xff); os_writec(orig_x0 >> 8);
	os_writec(orig_y0 & 0xff); os_writec(orig_y0 >> 8);
}


/**
 * Closes any open buffer and flushes the contents to screen
 */
void ro_gui_buffer_close(void) {

	/*	Check we have an open buffer
	*/
	if (!buffer)
		return;

	/*	Remove any previous redirection
	*/
	xosspriteop_switch_output_to_sprite(osspriteop_PTR,
			context1, context2, context3,
			0, 0, 0, 0);
	free(save_area);

	/*	Plot the contents to screen
	*/
	if (mode == tinct_SPRITE_MODE)
		_swix(Tinct_Plot, _IN(2) | _IN(3) | _IN(4) | _IN(7),
				(char *)(buffer + 1),
				clipping.x0, clipping.y0,
				option_fg_plot_style);
	else
		xosspriteop_put_sprite_user_coords(osspriteop_PTR,
			buffer, (osspriteop_id)(buffer + 1),
			clipping.x0, clipping.y0, (os_action)0);
	ro_gui_buffer_free();
}


/**
 * Releases any buffer memory depending on cache constraints.
 */
static void ro_gui_buffer_free(void) {
	free(buffer);
	buffer = NULL;
}