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engines/sword2/scroll.cpp

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+/* ScummVM - Graphic Adventure Engine
+ *
+ * ScummVM is the legal property of its developers, whose names
+ * are too numerous to list here. Please refer to the COPYRIGHT
+ * file distributed with this source distribution.
+ *
+ * Additional copyright for this file:
+ * Copyright (C) 1994-1998 Revolution Software Ltd.
+ *
+ * This program 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, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * This program 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/>.
+ */
+
+
+
+#include "sword2/sword2.h"
+#include "sword2/defs.h"
+#include "sword2/header.h"
+#include "sword2/logic.h"
+#include "sword2/screen.h"
+
+namespace Sword2 {
+
+// Max no of pixel allowed to scroll per cycle
+#define MAX_SCROLL_DISTANCE 8
+
+/**
+ * Sets the scroll target position for the end of the game cycle. The driver
+ * will then automatically scroll as many times as it can to reach this
+ * position in the allotted time.
+ */
+
+void Screen::setScrollTarget(int16 sx, int16 sy) {
+	_scrollXTarget = sx;
+	_scrollYTarget = sy;
+}
+
+/**
+ * If the room is larger than the physical screen, this function is called
+ * every game cycle to update the scroll offsets.
+ */
+
+void Screen::setScrolling() {
+	// Normally we aim to get George's feet at (320,250) from top left
+	// of screen window
+	// feet_x = 128 + 320
+	// feet_y = 128 + 250
+
+	// Set scroll offsets according to the player's coords
+
+	// If the scroll offsets are being forced in script, ensure that they
+	// are neither too far to the right nor too far down.
+	uint32 scrollX = _vm->_logic->readVar(SCROLL_X);
+	uint32 scrollY = _vm->_logic->readVar(SCROLL_Y);
+
+	if (scrollX || scrollY) {
+		_thisScreen.scroll_offset_x = MIN((uint16)scrollX, _thisScreen.max_scroll_offset_x);
+		_thisScreen.scroll_offset_y = MIN((uint16)scrollY, _thisScreen.max_scroll_offset_y);
+		return;
+	}
+
+	// George's offset from the center - the desired position for him
+
+	int16 offset_x = _thisScreen.player_feet_x - _thisScreen.feet_x;
+	int16 offset_y = _thisScreen.player_feet_y - _thisScreen.feet_y;
+
+	// Prevent scrolling too far left/right/up/down
+
+	if (offset_x < 0)
+		offset_x = 0;
+	else if (offset_x > _thisScreen.max_scroll_offset_x)
+		offset_x = _thisScreen.max_scroll_offset_x;
+
+	if (offset_y < 0)
+		offset_y = 0;
+	else if (offset_y > _thisScreen.max_scroll_offset_y)
+		offset_y = _thisScreen.max_scroll_offset_y;
+
+	// First time on this screen - need absolute scroll immediately!
+
+	if (_thisScreen.scroll_flag == 2) {
+		debug(5, "init scroll");
+		_thisScreen.scroll_offset_x = offset_x;
+		_thisScreen.scroll_offset_y = offset_y;
+		_thisScreen.scroll_flag = 1;
+		return;
+	}
+
+	// Catch up with required scroll offsets - speed depending on distance
+	// to catch up (dx and dy) and _scrollFraction used, but limit to
+	// certain number of pixels per cycle (MAX_SCROLL_DISTANCE)
+
+	int16 dx = _thisScreen.scroll_offset_x - offset_x;
+	int16 dy = _thisScreen.scroll_offset_y - offset_y;
+
+	uint16 scroll_distance_x;	// how much we want to scroll
+	uint16 scroll_distance_y;
+
+	if (dx < 0) {
+		// Current scroll_offset_x is less than the required value
+
+		// NB. I'm adding 1 to the result of dx / SCROLL_FRACTION,
+		// because it would otherwise not scroll at all when
+		// dx < SCROLL_FRACTION
+
+		// => inc by (fraction of the differnce) NB. dx is -ve, so we
+		// subtract dx / SCROLL_FRACTION
+
+		scroll_distance_x = 1 - dx / _scrollFraction;
+
+		if (scroll_distance_x > MAX_SCROLL_DISTANCE)
+			scroll_distance_x = MAX_SCROLL_DISTANCE;
+
+		_thisScreen.scroll_offset_x += scroll_distance_x;
+	} else if (dx > 0) {
+		// Current scroll_offset_x is greater than
+		// the required value
+
+		// => dec by (fraction of the differnce)
+
+		scroll_distance_x = 1 + dx / _scrollFraction;
+
+		if (scroll_distance_x > MAX_SCROLL_DISTANCE)
+			scroll_distance_x = MAX_SCROLL_DISTANCE;
+
+		_thisScreen.scroll_offset_x -= scroll_distance_x;
+	}
+
+	if (dy < 0) {
+		scroll_distance_y = 1 - dy / _scrollFraction;
+
+		if (scroll_distance_y > MAX_SCROLL_DISTANCE)
+			scroll_distance_y = MAX_SCROLL_DISTANCE;
+
+		_thisScreen.scroll_offset_y += scroll_distance_y;
+	} else if (dy > 0) {
+		scroll_distance_y = 1 + dy / _scrollFraction;
+
+		if (scroll_distance_y > MAX_SCROLL_DISTANCE)
+			scroll_distance_y = MAX_SCROLL_DISTANCE;
+
+		_thisScreen.scroll_offset_y -= scroll_distance_y;
+	}
+}
+
+} // End of namespace Sword2