193c5df75d
- Comment keymaps.h - Tie XWORLD_DEBUG into ROCKBOX_HAS_LOGF to ease debugging - Fix up the manual a little bit Change-Id: I12cfb58001199036cd67dbaa27f164e6790a199d Reviewed-on: http://gerrit.rockbox.org/1084 Reviewed-by: Michael Giacomelli <giac2000@hotmail.com>
244 lines
7.9 KiB
C
244 lines
7.9 KiB
C
/***************************************************************************
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* __________ __ ___.
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* Open \______ \ ____ ____ | | _\_ |__ _______ ___
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* Source | _// _ \_/ ___\| |/ /| __ \ / _ \ \/ /
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* Jukebox | | ( <_> ) \___| < | \_\ ( <_> > < <
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* Firmware |____|_ /\____/ \___ >__|_ \|___ /\____/__/\_ \
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* \/ \/ \/ \/ \/
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* $Id$
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*
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* Copyright (C) 2014 Franklin Wei, Benjamin Brown
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* Copyright (C) 2004 Gregory Montoir
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*
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* This program is free software; you can redistribute it and/or
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* modify it under the terms of the GNU General Public License
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* as published by the Free Software Foundation; either version 2
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* of the License, or (at your option) any later version.
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*
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* This software is distributed on an "AS IS" basis, WITHOUT WARRANTY OF ANY
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* KIND, either express or implied.
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*
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***************************************************************************/
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#include "plugin.h"
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#include "engine.h"
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#include "sys.h"
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#include "util.h"
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/* we don't want these on the stack, they're big and could cause a stack overflow */
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static struct Engine e;
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static struct System sys;
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enum plugin_status plugin_start(const void* parameter)
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{
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(void) parameter;
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/* no trailing slashes */
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const char *dataPath = "/.rockbox/xworld";
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const char *savePath = "/.rockbox/xworld";
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g_debugMask = XWORLD_DEBUGMASK;
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engine_create(&e, &sys, dataPath, savePath);
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engine_init(&e);
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sys_menu(&sys);
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engine_run(&e);
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engine_finish(&e);
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return PLUGIN_OK;
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}
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/*
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Game was originally made with 16. SIXTEEN colors. Running on 320x200 (64,000 pixels.)
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Great fan site here: https://sites.google.com/site/interlinkknight/anotherworld
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Contains the wheelcode :P !
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A lot of details can be found regarding the game and engine architecture at:
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http://www.anotherworld.fr/anotherworld_uk/another_world.htm
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The chronology of the game implementation can retraced via the ordering of the opcodes:
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The sound and music opcode are at the end: Music and sound was done at the end.
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Call tree:
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=========
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SDLSystem systemImplementaion ;
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System *sys = & systemImplementaion ;
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main
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{
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Engine *e = new Engine();
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e->run()
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{
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sys->init("Out Of This World");
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setup();
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vm.restartAt(0x3E80); // demo starts at 0x3E81
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while (!_stub->_pi.quit)
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{
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vm.setupScripts();
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vm.inp_updatePlayer();
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processInput();
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vm.runScripts();
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}
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finish();
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}
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}
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Virtual Machine:
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================
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Seems the threading model is collaborative multi-tasking (as opposed to preemptive multitasking):
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A thread (called a Channel on Eric Chahi's website) will release the hand to the next one via the
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break opcode.
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It seems that even when a setvec is requested by a thread, we cannot set the instruction pointer
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yet. The thread is allowed to keep on executing its code for the remaining of the vm frame.
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A virtual machine frame has a variable duration. The unit of time is 20ms and the frame can be set
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to live for 1 (20ms ; 50Hz) up to 5 (100ms ; 10Hz).
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There are 30 something opcodes. The graphic opcode are more complex, not only the declare the operation to perform
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they also define where to find the vertices (segVideo1 or segVideo2).
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No stack available but a thread can save its pc (Program Counter) once: One method call and return is possible.
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Video :
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=======
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Double buffer architecture. AW opcodes even has a special instruction for blitting from one
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frame buffer to an other.
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Double buffering is implemented in software
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According to Eric Chahi's webpage there are 4 framebuffer. Since on full screenbuffer is 320x200/2 = 32kB
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that would mean the total size consumed is 128KB ?
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Sound :
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=======
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Mixing is done on software.
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Since the virtual machine and SDL are running simultaneously in two different threads:
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Any read or write to an elements of the sound channels MUST be synchronized with a
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mutex.
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FastMode :
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==========
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The game engine features a "fast-mode"...what it to be able to respond to the now defunct
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TURBO button commonly found on 386/486 era PC ?!
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Endianess:
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==========
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Atari and Amiga used bigEndian CPUs. Data are hence stored within BANK in big endian format.
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On an Intel or ARM CPU data will have to be transformed when read.
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The original codebase contained a looooot of cryptic hexa values.
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0x100 (for 256 variables)
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0x400 (for one kilobyte)
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0x40 (for num threads)
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0x3F (num thread mask)
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I cleaned that up.
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Questions & Answers :
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=====================
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Q: How does the interpreter deals with the CPU speed ?! A pentium is a tad faster than a Motorola 68000
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after all.
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A: See vm frame time: The vm frame duration is variable. The vm actually write for how long a video frame
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should be displayed in variable 0xFF. The value is the number of 20ms slice
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Q: Why is a palette 2048 bytes if there are only 16 colors ? I would have expected 48 bytes...
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A: ???
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Q: Why does Resource::load() search for ressource to load from higher to lower....since it will load stuff
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until no more ressources are marked as "Need to be loaded".
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A: ???
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Original DOS version :
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======================
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Banks: 1,236,519 B
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exe : 20,293 B
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Total bank size: 1236519 (100%)
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---------------------------------
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Total RT_SOUND size: 585052 ( 47%)
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Total RT_MUSIC size: 3540 ( 0%)
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Total RT_POLY_ANIM size: 106676 ( 9%)
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Total RT_PALETTE size: 11032 ( 1%)
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Total RT_BYTECODE size: 135948 ( 11%)
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Total RT_POLY_CINEMATIC size: 291008 ( 24%)
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As usual sounds are the most consuming assets (Quake1,Quake2 etc.....)
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memlist.bin features 146 entries :
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==================================
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Most important part in an entry are:
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bankId : - Give the file were the resource is.
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offset : - How much to skip in the file before hiting the resource.
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size,packetSize : - How much to read, should we unpack what we read.
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Polygons drawing :
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=================
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Polygons can be given as:
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- a pure screenspace sequence of points: I call those screenspace polygons.
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- a list of delta to add or substract to the first vertex. I call those: objectspace polygons.
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Video :
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=======
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Q: Why 4 framebuffer ?
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A: It seems the background is generated once (like in the introduction) and stored in a framebuffer.
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Every frame the saved background is copied and new elements are drawn on top.
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Trivia :
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========
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If you are used to RGBA 32bits per pixel framebuffer you are in for a shock:
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Another world is 16 colors palette based, making it 4bits per pixel !!
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Video generation :
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==================
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Thank god the engine sets the palette before starting to drawing instead of after bliting.
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I would have been unable to generate screenshots otherwise.
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Memory managment :
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=================
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There is 0 malloc during the game. All resources are loaded in one big buffer (Resource::load).
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The entire buffer is "freed" at the end of a game part.
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The renderer is actually capable of Blending a new poly in the framebuffer (Video::drawLineT)
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I am almost sure that:
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_curPagePtr1 is the backbuffer
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_curPagePtr2 is the frontbuffer
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_curPagePtr3 is the background builder.
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* Why does memlist.bin uses a special state field 0xFF in order to mark the end of resources ??!
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It would have been so much easier to write the number of resources at the beginning of the code.
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*/
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