Monday, July 29, 2013

“One person's data is another person's noise.”

I know it's been forever since I've done a post and I'm really sorry. I got caught up in the sound issues and panorama issues. I'm going to talk about sound in this post and then make another post about panoramas. So here we go!

“One person's data is another person's noise.”  ― K.C. Cole

This quote pretty much sums up my experiences with the sound decoding. I was somewhat lucky in that Marisa Chan's source code had an implementation of sound decoding that I could model off of, but at the same time, the whole function was quite cryptic. This is mostly due to the variable "naming". And I say "naming" in the loosest sense of the word, because most were single letters:

void adpcm8_decode(void *in, void *out, int8_t stereo, int32_t n)
    uint8_t *m1;
    uint16_t *m2;
    m1 = (uint8_t *)in;
    m2 = (uint16_t *)out;
    uint32_t a, x, j = 0;
    int32_t b, i, t[4] = {0, 0, 0, 0};

    while (n)
        a = *m1;
        i = t[j+2];
        x = t2[i];
        b = 0;

        if(a & 0x40)
            b += x;
        if(a & 0x20)
            b += x >> 1;
        if(a & 0x10)
            b += x >> 2;
        if(a & 8)
            b += x >> 3;
        if(a & 4)
            b += x >> 4;
        if(a & 2)
            b += x >> 5;
        if(a & 1)
            b += x >> 6;

        if(a & 0x80)
            b = -b;

        b += t[j];

        if(b > 32767)
            b = 32767;
        else if(b < -32768)
            b = -32768;

        i += t1[(a >> 4) & 7];

        if(i < 0)
            i = 0;
        else if(i > 88)
            i = 88;

        t[j] = b;
        t[j+2] = i;
        j = (j + 1) & stereo;
        *m2 = b;


No offense intended towards Marisa Chan, but that makes my eyes hurt. It made understanding the algorithm that much harder. But after talking to a couple people at ScummVM and Wikipedia-ing general sound decoding, I figured out the sound is encoded using a modified Microsoft Adaptive PCM. I'll go ahead and post my implementation and then describe the process:

const int16 RawZorkStream::_stepAdjustmentTable[8] = {-1, -1, -1, 1, 4, 7, 10, 12};

const int32 RawZorkStream::_amplitudeLookupTable[89] = {0x0007, 0x0008, 0x0009, 0x000A, 0x000B, 0x000C, 0x000D, 0x000E,
                                                        0x0010, 0x0011, 0x0013, 0x0015, 0x0017, 0x0019, 0x001C, 0x001F,
                                                        0x0022, 0x0025, 0x0029, 0x002D, 0x0032, 0x0037, 0x003C, 0x0042,
                                                        0x0049, 0x0050, 0x0058, 0x0061, 0x006B, 0x0076, 0x0082, 0x008F,
                                                        0x009D, 0x00AD, 0x00BE, 0x00D1, 0x00E6, 0x00FD, 0x0117, 0x0133, 
                                                        0x0151, 0x0173, 0x0198, 0x01C1, 0x01EE, 0x0220, 0x0256, 0x0292,
                                                        0x02D4, 0x031C, 0x036C, 0x03C3, 0x0424, 0x048E, 0x0502, 0x0583, 
                                                        0x0610, 0x06AB, 0x0756, 0x0812, 0x08E0, 0x09C3, 0x0ABD, 0x0BD0,
                                                        0x0CFF, 0x0E4C, 0x0FBA, 0x114C, 0x1307, 0x14EE, 0x1706, 0x1954, 
                                                        0x1BDC, 0x1EA5, 0x21B6, 0x2515, 0x28CA, 0x2CDF, 0x315B, 0x364B,
                                                        0x3BB9, 0x41B2, 0x4844, 0x4F7E, 0x5771, 0x602F, 0x69CE, 0x7462, 0x7FFF};

int RawZorkStream::readBuffer(int16 *buffer, const int numSamples) {
    uint32 bytesRead = 0;

    // 0: Left, 1: Right
    byte channel = 0;

    while (bytesRead < numSamples) {
        byte encodedSample = _stream->readByte();
        if (_stream->eos()) {
            _endOfData = true;
            return bytesRead;

        int16 index = _lastSample[channel].index;
        uint32 lookUpSample = _amplitudeLookupTable[index];

        int32 sample = 0;

        if (encodedSample & 0x40)
            sample += lookUpSample;
        if (encodedSample & 0x20)
            sample += lookUpSample >> 1;
        if (encodedSample & 0x10)
            sample += lookUpSample >> 2;
        if (encodedSample & 8)
            sample += lookUpSample >> 3;
        if (encodedSample & 4)
            sample += lookUpSample >> 4;
        if (encodedSample & 2)
            sample += lookUpSample >> 5;
        if (encodedSample & 1)
            sample += lookUpSample >> 6;
        if (encodedSample & 0x80)
            sample = -sample;

        sample += _lastSample[channel].sample;
        sample = CLIP(sample, -32768, 32767);

        buffer[bytesRead - 1] = (int16)sample;

        index += _stepAdjustmentTable[(encodedSample >> 4) & 7];
        index = CLIP<int16>(index, 0, 88);

        _lastSample[channel].sample = sample;
        _lastSample[channel].index = index;

        // Increment and wrap the channel
        channel = (channel + 1) & _stereo;

    return bytesRead;

Each sample is encoded into 8 bits. The actual sound sample is read from the bits using a lookup table and an index from the previous 'frame'. This is then added to the sample from last 'frame'. Finally, the 4 high bits are used to set the index for the next 'frame'.

The biggest problem I ran into for sound was actually a typo on my part. The template argument for CLIP was accidentally set to a uint16 instead of a int16. This caused distortions at the extremely high and low ranges of the sound. But, this usually only occurred at the beginning and end of a sound clip. I spent days trying to figure out if I had set the initial lastSample correctly, or other random ideas. After pounding my head into the desk for 3 days, the glorious wjp came along and found my typo. After which, the sound worked perfectly. Shout out to wjp!!!!!!!!!

There is one other bug with sound and that's in videos. The sound has a slight 'ticking'. However, clone2727 identified it potentially as a problem with the AVI decoder. In the current state, the AVI decoder puts each sound 'chunk' into its own AudioStream, and then puts all the streams into a queue to be played. We're thinking the lastSample needs to persist from chunk to chunk. However, solving this problem would take either a gross hack, or a redesign of the AVI decoder. clone2727 has taken on the task, so I'm going to leave it to him and get back to the video audio later in the project.

Well, that's it for this post. Sound was pretty straightforward. I was only bogged down due to some really bad typos on my part. As always, feel free to comment or ask questions.


Wednesday, July 17, 2013

The Engine Skeleton Gains Some Tendons - Part 2

Part 2!! As a recap from last post, I started out last week by implementing image handling, video handling, and a text debug console.

I started with the console as it allows me to to map typed commands to functions. (IE. 'loadimage zassets/castle/cae4d311.tga' calls loadImageToScreen() on that file) This is extremely useful in that I can load an image multiple times or I can load different images all without having to re-run the engine or recompile.

Creating the text console was actually extremely easy because it was already written. I just to inherit from the base class:
class Console : public GUI::Debugger {
    Console(ZEngine *engine);
    virtual ~Console() {}

    ZEngine *_engine;

    bool cmdLoadImage(int argc, const char **argv);
    bool cmdLoadVideo(int argc, const char **argv);
    bool cmdLoadSound(int argc, const char **argv);

In the constructor, I just registered the various commands:
Console::Console(ZEngine *engine) : GUI::Debugger(), _engine(engine) {
    DCmd_Register("loadimage", WRAP_METHOD(Console, cmdLoadImage));
    DCmd_Register("loadvideo", WRAP_METHOD(Console, cmdLoadVideo));
    DCmd_Register("loadsound", WRAP_METHOD(Console, cmdLoadSound));

And then, in ZEngine::initialize() I created an instance of my custom class:
void ZEngine::initialize() {

    _console = new Console(this);

And lastly, I registered a key press combination to bring up the debug console
void ZEngine::processEvents() {
    while (_eventMan->pollEvent(_event)) {
        switch (_event.type) {
        case Common::EVENT_KEYDOWN:
            switch (_event.kbd.keycode) {
            case Common::KEYCODE_d:
                if (_event.kbd.hasFlags(Common::KBD_CTRL)) {
                    // Start the debugger

With that done, I can press ctrl+d, and this is what pops up:

Awesome! With that done, I could move on to images. All the images in ZNem and ZGI are .tga files, but don't be fooled; the vast majority of them aren't actually TGA. They're actually TGZ, a custom image format. The format itself isn't too difficult, and I give all the credit to Mr. Mouse on Xentax.
Byte[4] "TGZ\0"
uint32 Original size of bitmap data
uint32 Width of image
uint32 Heigth of image
Byte[n] Bitmap data (LZSS compressed)

I could have created a class for decoding TGZ, but with it being that simple, I just chose to integrate the decoding in the renderImageToScreen method:
void ZEngine::renderImageToScreen(const Common::String &fileName, uint32 x, uint32 y) {
    Common::File file;

    if (! {
        error("Could not open file %s", fileName.c_str());

    // Read the magic number
    // Some files are true TGA, while others are TGZ
    char fileType[4];, 4);

    // Check for TGZ files
    if (fileType[0] == 'T' && fileType[1] == 'G' && fileType[2] == 'Z' && fileType[3] == '\0') {
        // TGZ files have a header and then Bitmap data that is compressed with LZSS
        uint32 decompressedSize = file.readSint32LE();
        uint32 width = file.readSint32LE();
        uint32 height = file.readSint32LE();

        LzssReadStream stream(&file);
        byte *buffer = new byte[decompressedSize];, decompressedSize);

        _system->copyRectToScreen(buffer, width * 2, x, y, width, height);
    } else {
        // Reset the cursor;

        // Decode
        Graphics::TGADecoder tga;
        if (!tga.loadStream(file)) {
            error("Error while reading TGA image");

        const Graphics::Surface *tgaSurface = tga.getSurface();
        _system->copyRectToScreen(tgaSurface->pixels, tgaSurface->pitch, x, y, tgaSurface->w, tgaSurface->h);


    _needsScreenUpdate = true;

So after using the loadimage command in the console, we get a wonderful picture on the screen:

Video!! Implementing the image aspect of video was rather trivial, as ZEngine uses a standard AVI format. The only 'wrinkle' was that the videos used a different PixelFormat. Every other part of the engine uses RGB 555, but videos use RGB 565. However, when a video is playing, it's only thing going on. So, I can reinitialize the graphics to RGB 565 before playing a video, and reset it back to RGB 555 when the video finishes:
void ZEngine::startVideo(Video::VideoDecoder *videoDecoder) {
    if (!videoDecoder)

    _currentVideo = videoDecoder;

    Common::List formats;
    initGraphics(_width, _height, true, formats);
void ZEngine::continueVideo() {

    if (!_currentVideo->endOfVideo()) {
        // Code to render the current frame
    } else {
        initGraphics(_width, _height, true, &_pixelFormat);
        delete _currentVideo;
        _currentVideo = 0;
        delete _scaledVideoFrameBuffer;
        _scaledVideoFrameBuffer = 0;
Where _pixelFormat is a const PixelFormat member variable of the ZEngine class.

One other slight wrinkle is that the video is at a resolution of 256 x 160, which is quite small if I do say so myself. To fix that, I used a linear 2x scaler that [md5] wrote and scaled every frame. Using the opening cinematic as an example, we get this:

However, the sound in video is messed up, and it's actually been what I've been working on this week, but I'll save that for another post.

I'm now two steps closer to getting all the parts of the engine implemented and somewhat tied together. As always, if you have an suggestions or comments, feel free to comment below.


Thursday, July 11, 2013

The Engine Skeleton Gains Some Tendons - Part 1

Being a little tired of the script system, I started last week by adding image handling, video handling and a text debug console to the engine. With that done, I tried piecing together how the script system worked as a whole. After a long talk with Fuzzie, we figured out the majority of the system worked and I've spent the beginning of this week putting it into code.

I'll start with the script system since it's fresh in my mind. Rather than try to explain what I learned, I'll just explain my current understanding of the system and it's behavior.

The system is governed by five main containers:
Common::HashMap<uint32, byte> _globalState;

Common::List<ActionNode *> _activeNodes;

Common::HashMap<uint32, Common::Array<Puzzle *>> _referenceTable;

Common::Stack<Puzzle *> _puzzlesToCheck;

Common::List<Puzzle> _activePuzzles;

Common::List<Control> _activeControls;

_globalState holds the state of the entire game. Each key is a hash that can represent anything from a timer to whether a certain puzzle has been solved. The value depends on the what the key is, however, the vast majority are boolean states (0 or 1).

_activeNodes holds... wait for it... the active ActionNodes. Imagine that! Nodes are anything that needs to be processed over time. For example, a timer, an animation, etc. I'll explain further later in the post.

_referenceTable stores references to the Puzzles that certain globalState keys have. This can be thought of as a reverse of the Puzzle struct. A Puzzle stores a list of globalState keys to be checked. _referenceTable stores which Puzzles reference certain globalState keys. Why would we want to do this? It means that any puzzles loaded into the _reference table only have to be checked once, instead of every frame. When a value in _globalState is changed, it adds the referenced Puzzle to _puzzlesToCheck

_puzzlesToCheck holds the Puzzles whose Criteria we want to check against _globalState. This stack is exhausted every frame. It is filled either by _referenceTable or when we enter a new room.

_activePuzzles is where the room's Puzzles are stored. The Puzzle pointers in _referenceTable and _puzzlesToCheck point to here.

I realize that the descriptions are still a bit vague, so I figured I would go through an example of sorts and how the containers behave.

Every time we change rooms:
  1. Clear _referenceTable, _puzzlesToCheck, and _activePuzzles
  2. Open and parse the corresponding .scr file into Puzzle structs and store them in _activePuzzles. (See last three blog posts)
  3. Iterate through all the Puzzles and their Criteria and create references from a globalState key to the Puzzle. (See createReferenceTable below)
  4. Add all Puzzles to _puzzlesToCheck
void ScriptManager::createReferenceTable() {
    // Iterate through each Puzzle
    for (Common::List<Puzzle>::iterator activePuzzleIter = _activePuzzles.begin(); activePuzzleIter != _activePuzzles.end(); activePuzzleIter++) {
        Puzzle *puzzlePtr = &(*activePuzzleIter);

        // Iterate through each Criteria and add a reference from the criteria key to the Puzzle
        for (Common::List<Criteria>::iterator criteriaIter = activePuzzleIter->criteriaList.begin(); criteriaIter != (*activePuzzleIter).criteriaList.end(); criteriaIter++) {

            // If the argument is a key, add a reference to it as well
            if (criteriaIter->argument)

    // Remove duplicate entries
    for (Common::HashMap<uint32, Common::Array<Puzzle *>>::iterator referenceTableIter; referenceTableIter != _referenceTable.end(); referenceTableIter++) {

Every frame:
  1. Iterate through each ActionNode in _activeNodes and call process() on them
  2. If process() returns true, remove and delete the ActionNode
void ScriptManager::updateNodes(uint32 deltaTimeMillis) {
    // If process() returns true, it means the node can be deleted
    for (Common::List<ActionNode *>::iterator iter = _activeNodes.begin(); iter != _activeNodes.end();) {
        if ((*iter)->process(_engine, deltaTimeMillis)) {
            // Remove the node from _activeNodes, then delete it
            ActionNode *node = *iter;
            iter = _activeNodes.erase(iter);
            delete node;
        } else {
bool NodeTimer::process(ZEngine *engine, uint32 deltaTimeInMillis) {
    _timeLeft -= deltaTimeInMillis;

    if (_timeLeft <= 0) {
        engine->getScriptManager()->setStateValue(_key, 0);
        return true;

    return false;

  1. While _puzzlesToCheck is not empty, pop a Puzzle off the stack and check its Criteria against _globalState
  2. If any of the Criteria pass, call execute() on the corresponding ResultAction.
    • Some ResultAction's might create ActionNode's and add them to _activeNodes. IE ActionTimer

void ScriptManager::checkPuzzleCriteria() {
    while (!_puzzlesToCheck.empty()) {
        Puzzle *puzzle = _puzzlesToCheck.pop();
        // Check each Criteria
        for (Common::List<Criteria>::iterator iter = puzzle->criteriaList.begin(); iter != puzzle->criteriaList.end(); iter++) {
            bool criteriaMet = false;

            // Get the value to compare against
            byte argumentValue;
            if ((*iter).argument)
                argumentValue = getStateValue(iter->argument);
                argumentValue = iter->argument;

            // Do the comparison
            switch ((*iter).criteriaOperator) {
            case EQUAL_TO:
                criteriaMet = getStateValue(iter->key) == argumentValue;
            case NOT_EQUAL_TO:
                criteriaMet = getStateValue(iter->key) != argumentValue;
            case GREATER_THAN:
                criteriaMet = getStateValue(iter->key) > argumentValue;
            case LESS_THAN:
                criteriaMet = getStateValue(iter->key) < argumentValue;

            // TODO: Add logic for the different Flags (aka, ONCE_PER_INST)
            if (criteriaMet) {
                for (Common::List<ResultAction *>::iterator resultIter = puzzle->resultActions.begin(); resultIter != puzzle->resultActions.end(); resultIter++) {
bool ActionTimer::execute(ZEngine *zEngine) {
    zEngine->getScriptManager()->addActionNode(new NodeTimer(_key, _time));
    return true;

So that's the script system. I've tried to explain it in the best way possible, but if you guys have any questions or suggestions for my implementation, as always, feel free to comment.

Details on the image handling, video handling and the text debug console will be in Part 2, which should be up some time tomorrow. As always, thanks for reading. :)


Monday, July 1, 2013

Improving the 'Object' class (including renaming it) and using classes for ResultActions

Last week, I posted about using an 'Object' class to encapsulate the variable-typed arguments for ResultActions. You guys posted some awesome feedback and I used it to improve the class. First, I renamed the class to 'SingleValueContainer' so users have a better sense of what it is. Second, following Fuzzie's advice, I put all the values except for String, directly in the union. It's the same or less memory cost and results in less heap allocations.
union {
    bool boolVal;
    byte byteVal;
    int16 int16Val;
    uint16 uint16Val;
    int32 int32Val;
    uint32 uint32Val;
    float floatVal;
    double doubleVal;
    char *stringVal;
} _value;

You'll notice that the stringVal isn't actually a Common::String object, but rather a pointer to a char array. This saves a bit of memory at the cost of a couple strlen(), memcpy(), and String object assigment.
SingleValueContainer::SingleValueContainer(Common::String value) : _objectType(BYTE) {
    _value.stringVal = new char[value.size() + 1];
    memcpy(_value.stringVal, value.c_str(), value.size() + 1);
SingleValueContainer &SingleValueContainer::operator=(const Common::String &rhs) {
    if (_objectType != STRING) {
        _objectType = STRING;
        _value.stringVal = new char[rhs.size() + 1];
        memcpy(_value.stringVal, rhs.c_str(), rhs.size() + 1);

        return *this;

    uint32 length = strlen(_value.stringVal);
    if (length <= rhs.size() + 1) {
        memcpy(_value.stringVal, rhs.c_str(), rhs.size() + 1);
    } else {
        delete[] _value.stringVal;
        _value.stringVal = new char[rhs.size() + 1];
        memcpy(_value.stringVal, rhs.c_str(), rhs.size() + 1);

    return *this;
bool SingleValueContainer::getStringValue(Common::String *returnValue) const {
    if (_objectType !=  STRING)
        warning("'Object' is not storing a Common::String.");

    *returnValue = _value.stringVal;
    return true;

With those changes the class seems quite solid. (The full source can be found here and here). However, after seeing Zidane Sama's comment, I realized that there was a better way to tackle the problem than variant objects. Instead of trying to generalize the action types and arguments and storing them in structs, a better approach is to create a class for each action type with a common, "execute()" method that will be called by the scriptManager when the Criteria are met for an ResultAction.

I first created an interface base class that all the different types would inherit from:
class ResultAction {
    virtual ~ResultAction() {}
    virtual bool execute(ZEngine *zEngine) = 0;

Next, I created the individual classes for each type of ResultAction:
class ActionAdd : public ResultAction {
    ActionAdd(Common::String line);
    bool execute(ZEngine *zEngine);

    uint32 _key;
    byte _value;

The individual classes parse out any arguments in their constructor and store them in member variables. In execute(), they execute the logic pertaining to their action. A pointer to ZEngine is passed in order to give the method access to all the necessary tools (modifying graphics, scriptManager states, sounds, etc.)
class ResultAction {
ActionAdd::ActionAdd(Common::String line) {
    sscanf(line.c_str(), ":add(%u,%hhu)", &_key, &_value);

bool ActionAdd::execute(ZEngine *zEngine) {
    zEngine->getScriptManager()->addToStateValue(_key, _value);
    return true;

Thus, in the script file parser I can just look for the action type and then pass create an action type, passing the constructor the whole line:
while (!line.contains('}')) {
    // Parse for the action type
    if (line.matchString("*:add*", true)) {
    } else if (line.matchString("*:animplay*", true)) {
    } else if (.....)

While this means I have to create 20+ classes for all the different types of actions, I think this method nicely encapsulates and abstracts both the parsing and the action of the result.

I'm a bit sad that I'm not going to be using the 'SingleValueContainer' class, but if nothing else, I learned quite a bit while creating it. Plus, I won't be getting rid of it, so it might have a use somewhere else.

This coming week I need to finish creating all the classes and then try to finish the rest of the engine skeleton. As always, feel free to comment / ask questions.