Prepare to add some Newtonianity

At this point we have an application with

1x Ninja, walking around
1x sphere, hanging in the center of the screen
1x cube, flying around the sphere

That’s our “game”? Doubtely… So let’s make things move like in real world! Or just like that…

Requirements

First of all, go and get the Newton GD files. And unpack it… right to the source directory of our project! That’s right! I’m not insane and I’m aware you are going to put a lot of files in your project. But have no fear - you may always add them to .gitignore and skip them from being tracked in your Git repo:

source/newton-dynamics-master/applications
source/newton-dynamics-master/packages/projects
source/newton-dynamics-master/packages/thirdParty
source/newton-dynamics-master/coreLibrary_300/projects

You are using Git, right?.. Now, you place the Newton GD sources in your project directory and change your CMakeLists.txt file to look like this:

cmake_minimum_required(VERSION 3.1)
project(irrlicht_newton_game1)

set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -std=c++11")

option("NEWTON_DEMOS_SANDBOX" "Build demos sandbox" OFF)

set(NEWTONGD_PATH source/newton-dynamics-master)
set(NEWTONGD_INCLUDE_DIRS
        ${NEWTONGD_PATH}/packages/dCustomJoints
        ${NEWTONGD_PATH}/packages/dContainers
        ${NEWTONGD_PATH}/packages/dMath
        )

set(NEWTON_LIBRARIES Newton dMath)

add_subdirectory(${NEWTONGD_PATH})

find_package(X11)
find_package(OpenGL)
find_package(ZLIB)

if (NOT IRRLICHT_LIBRARY_PATH)
    find_library(IRRLICHT_LIBRARY_PATH
            NAMES Irrlicht
            PATHS ${IRRLICHT_PATH}/lib/
            PATH_SUFFIXES Linux MacOSX Win32-gcc Win32-visualstudio Win64-visualstudio)

    message(STATUS "Found Irrlicht: ${IRRLICHT_LIBRARY_PATH}")
endif()

include_directories(${IRRLICHT_PATH}/include ${NEWTONGD_INCLUDE_DIRS})

set(SOURCE_FILES source/main.cpp)
set(EXECUTABLE_NAME irrlicht_newton_game1)

add_executable(${EXECUTABLE_NAME} ${SOURCE_FILES})

target_link_libraries(${EXECUTABLE_NAME}
        ${NEWTON_LIBRARIES}
        ${IRRLICHT_LIBRARY_PATH}
        ${X11_LIBRARIES}
        ${OPENGL_LIBRARIES}
        ${ZLIB_LIBRARIES}
        ${X11_Xxf86vm_LIB})

Try to compile your project - it should be just fine. And observe the power of CMake!

Gravity

Let’s start modifying our Irrlicht sample application. First of all, we will add some Newton headers:

#include "newton-dynamics-master/coreLibrary_300/source/newton/Newton.h"
#include "newton-dynamics-master/packages/dMath/dVector.h"
#include "newton-dynamics-master/packages/dMath/dMatrix.h"
#include "newton-dynamics-master/packages/dMath/dQuaternion.h"

The basic thing in the whole Newton GD library is NewtonWorld. That is what it means - the world, where all the physics happen. It is something different from where we place our 3D models. And that should be obvious - graphics are managed by Irrlicht and physics - by Newton. Those are totally different libraries. So we need to tie those two so that graphics correspond to what happens in physical world.

First of all, we need to have a variable for our NewtonWorld. And since physics are handled by scripts too, we need to have that variable close to our other objects - in the ScriptManager class.

There are two functions we need to bind to our NewtonBody:

static void transformCallback(const NewtonBody* body, const dFloat* matrix, int threadIndex) {
    // update ISceneNode so that it is in the same position and rotation as the NewtonBody
}

static void applyForceAndTorqueCallback(const NewtonBody* body, dFloat timestep, int threadIndex) {
    // just add gravity to our body
    dFloat Ixx, Iyy, Izz;
    dFloat mass;

    NewtonBodyGetMassMatrix(body, &mass, &Ixx, &Iyy, &Izz);

    dVector gravityForce(0.0f, mass * -9.8f, 0.0f, 1.0f);
    NewtonBodySetForce(body, &gravityForce[0]);
}

The first one, transformCallback, is called whenever body changes its transform - e. g. either position or rotation. This is a good place to synchronize our Irrlicht meshes’ positions with their Newton bodies.

The applyForceAndTorqueCallback function is called on each NewtonUpdate to set the final forces and torques for bodies. We will modify this one later, but for now its implementation is just good.

But what’s with that NewtonUpdate? This is a function, which does as it says: it updates NewtonWorld and all its bodies, taking into account the time since the last update. This function call has one great candidate to be placed into: handleFrame. But we need to modify that method to receive the time since the last frame been rendered and we will use this time to update NewtonWorld too.

private:
    void updatePhysics(float dt) {
         NewtonUpdate(newtonWorld, dt);
    }

public:
    void handleFrame(float dt) {
        auto handler = luaState.GetGlobalEnvironment().Get<LuaFunction<void(void)>>("handleFrame");

        updatePhysics(dt);
        setKeyStates();

        handler.Invoke();
    }

Remember about architecture: everything, what needs to be exposed to our scripts should be declared as public in our ScriptManager. Everything else - as protected or private. This is the basic principle of encapsulation, so let’s keep it in our application.

And update the main application loop:

while (device->run()) {
    // Work out a frame delta time.
    const u32 now = device->getTimer()->getTime();
    const f32 frameDeltaTime = (f32) (now - then);
    then = now;

    // ...

    scriptMgr->handleFrame(frameDeltaTime);

    // ...
}

Hint: to make simulation slower and so watch ball falling in detail, make the NewtonUpdate argument even smaller. Thousand times, say.

Since we have initialization for our Newton stuff, we need to clean it up at the exit to prevent memory leaks. Let’s declare a method for that:

private:
    void stopPhysics() {
        NewtonDestroyAllBodies(newtonWorld);
        NewtonDestroy(newtonWorld);
    }

And call it right before the program’s end:

device->drop();

scriptMgr->handleExit();
delete scriptMgr;

And now is the right moment to add key codes’ definitions and exit function to our ScriptManager so that we could write more clear code and close our application correctly, using, say, Esc key.

To stop our application, we need to break our while (device->run()) loop. This could be achieved by simply closing the IrrlichtDevice with device->closeDevice(). But we do not have an access to the device from the ScriptManager. So let’s add it as a constructor argument:

private:
    irr::IrrlichtDevice *device;

public:
    ScriptManager(irr::IrrlichtDevice *_device, scene::ISceneManager *_smgr, video::IVideoDriver *_driver) {
        driver = _driver;
        smgr = _smgr;
        device = _device;

        initPhysics();
    }

So now we can create a function, exposed to our scripts, which will stop our application:

void exit() {
    device->closeDevice();
}

And bind it to the Lua function:

auto exitFn = luaState.CreateFunction<void(void)>(
                [&]() -> void { exit(); });

global.Set("exit", exitFn);

Now we can use our exit function in the Lua scripts. But we will need to use hexadecimal key codes and that’s… ugly. So we need to define some symbolic names for those codes:

void setGlobalVariables() {
    setKeyStates();
    setKeyCodeConstants();
}

void setKeyCodeConstants() {
    std::map<std::string, int> keyMapping = {
        { "KEY_LBUTTON", 0x01 }, // Left mouse button
        { "KEY_RBUTTON", 0x02 }, // Right mouse button
        { "KEY_CANCEL", 0x03 }, // Control-break processing
        { "KEY_MBUTTON", 0x04 }, // Middle mouse button (three-button mouse)
        { "KEY_XBUTTON1", 0x05 }, // Windows 2000/XP: X1 mouse button
        { "KEY_XBUTTON2", 0x06 }, // Windows 2000/XP: X2 mouse button
        { "KEY_BACK", 0x08 }, // BACKSPACE key
        { "KEY_TAB", 0x09 }, // TAB key
        { "KEY_CLEAR", 0x0C }, // CLEAR key
        { "KEY_RETURN", 0x0D }, // ENTER key
        { "KEY_SHIFT", 0x10 }, // SHIFT key
        { "KEY_CONTROL", 0x11 }, // CTRL key
        { "KEY_MENU", 0x12 }, // ALT key
        { "KEY_PAUSE", 0x13 }, // PAUSE key
        { "KEY_CAPITAL", 0x14 }, // CAPS LOCK key
        { "KEY_KANA", 0x15 }, // IME Kana mode
        { "KEY_HANGUEL", 0x15 }, // IME Hanguel mode (maintained for compatibility use KEY_HANGUL)
        { "KEY_HANGUL", 0x15 }, // IME Hangul mode
        { "KEY_JUNJA", 0x17 }, // IME Junja mode
        { "KEY_FINAL", 0x18 }, // IME final mode
        { "KEY_HANJA", 0x19 }, // IME Hanja mode
        { "KEY_KANJI", 0x19 }, // IME Kanji mode
        { "KEY_ESCAPE", 0x1B }, // ESC key
        { "KEY_CONVERT", 0x1C }, // IME convert
        { "KEY_NONCONVERT", 0x1D }, // IME nonconvert
        { "KEY_ACCEPT", 0x1E }, // IME accept
        { "KEY_MODECHANGE", 0x1F }, // IME mode change request
        { "KEY_SPACE", 0x20 }, // SPACEBAR
        { "KEY_PRIOR", 0x21 }, // PAGE UP key
        { "KEY_NEXT", 0x22 }, // PAGE DOWN key
        { "KEY_END", 0x23 }, // END key
        { "KEY_HOME", 0x24 }, // HOME key
        { "KEY_LEFT", 0x25 }, // LEFT ARROW key
        { "KEY_UP", 0x26 }, // UP ARROW key
        { "KEY_RIGHT", 0x27 }, // RIGHT ARROW key
        { "KEY_DOWN", 0x28 }, // DOWN ARROW key
        { "KEY_SELECT", 0x29 }, // SELECT key
        { "KEY_PRINT", 0x2A }, // PRINT key
        { "KEY_EXECUT", 0x2B }, // EXECUTE key
        { "KEY_SNAPSHOT", 0x2C }, // PRINT SCREEN key
        { "KEY_INSERT", 0x2D }, // INS key
        { "KEY_DELETE", 0x2E }, // DEL key
        { "KEY_HELP", 0x2F }, // HELP key
        { "KEY_KEY_0", 0x30 }, // 0 key
        { "KEY_KEY_1", 0x31 }, // 1 key
        { "KEY_KEY_2", 0x32 }, // 2 key
        { "KEY_KEY_3", 0x33 }, // 3 key
        { "KEY_KEY_4", 0x34 }, // 4 key
        { "KEY_KEY_5", 0x35 }, // 5 key
        { "KEY_KEY_6", 0x36 }, // 6 key
        { "KEY_KEY_7", 0x37 }, // 7 key
        { "KEY_KEY_8", 0x38 }, // 8 key
        { "KEY_KEY_9", 0x39 }, // 9 key
        { "KEY_KEY_A", 0x41 }, // A key
        { "KEY_KEY_B", 0x42 }, // B key
        { "KEY_KEY_C", 0x43 }, // C key
        { "KEY_KEY_D", 0x44 }, // D key
        { "KEY_KEY_E", 0x45 }, // E key
        { "KEY_KEY_F", 0x46 }, // F key
        { "KEY_KEY_G", 0x47 }, // G key
        { "KEY_KEY_H", 0x48 }, // H key
        { "KEY_KEY_I", 0x49 }, // I key
        { "KEY_KEY_J", 0x4A }, // J key
        { "KEY_KEY_K", 0x4B }, // K key
        { "KEY_KEY_L", 0x4C }, // L key
        { "KEY_KEY_M", 0x4D }, // M key
        { "KEY_KEY_N", 0x4E }, // N key
        { "KEY_KEY_O", 0x4F }, // O key
        { "KEY_KEY_P", 0x50 }, // P key
        { "KEY_KEY_Q", 0x51 }, // Q key
        { "KEY_KEY_R", 0x52 }, // R key
        { "KEY_KEY_S", 0x53 }, // S key
        { "KEY_KEY_T", 0x54 }, // T key
        { "KEY_KEY_U", 0x55 }, // U key
        { "KEY_KEY_V", 0x56 }, // V key
        { "KEY_KEY_W", 0x57 }, // W key
        { "KEY_KEY_X", 0x58 }, // X key
        { "KEY_KEY_Y", 0x59 }, // Y key
        { "KEY_KEY_Z", 0x5A }, // Z key
        { "KEY_LWIN", 0x5B }, // Left Windows key (Microsoft� Natural� keyboard)
        { "KEY_RWIN", 0x5C }, // Right Windows key (Natural keyboard)
        { "KEY_APPS", 0x5D }, // Applications key (Natural keyboard)
        { "KEY_SLEEP", 0x5F }, // Computer Sleep key
        { "KEY_NUMPAD0", 0x60 }, // Numeric keypad 0 key
        { "KEY_NUMPAD1", 0x61 }, // Numeric keypad 1 key
        { "KEY_NUMPAD2", 0x62 }, // Numeric keypad 2 key
        { "KEY_NUMPAD3", 0x63 }, // Numeric keypad 3 key
        { "KEY_NUMPAD4", 0x64 }, // Numeric keypad 4 key
        { "KEY_NUMPAD5", 0x65 }, // Numeric keypad 5 key
        { "KEY_NUMPAD6", 0x66 }, // Numeric keypad 6 key
        { "KEY_NUMPAD7", 0x67 }, // Numeric keypad 7 key
        { "KEY_NUMPAD8", 0x68 }, // Numeric keypad 8 key
        { "KEY_NUMPAD9", 0x69 }, // Numeric keypad 9 key
        { "KEY_MULTIPLY", 0x6A }, // Multiply key
        { "KEY_ADD", 0x6B }, // Add key
        { "KEY_SEPARATOR", 0x6C }, // Separator key
        { "KEY_SUBTRACT", 0x6D }, // Subtract key
        { "KEY_DECIMAL", 0x6E }, // Decimal key
        { "KEY_DIVIDE", 0x6F }, // Divide key
        { "KEY_F1", 0x70 }, // F1 key
        { "KEY_F2", 0x71 }, // F2 key
        { "KEY_F3", 0x72 }, // F3 key
        { "KEY_F4", 0x73 }, // F4 key
        { "KEY_F5", 0x74 }, // F5 key
        { "KEY_F6", 0x75 }, // F6 key
        { "KEY_F7", 0x76 }, // F7 key
        { "KEY_F8", 0x77 }, // F8 key
        { "KEY_F9", 0x78 }, // F9 key
        { "KEY_F10", 0x79 }, // F10 key
        { "KEY_F11", 0x7A }, // F11 key
        { "KEY_F12", 0x7B }, // F12 key
        { "KEY_F13", 0x7C }, // F13 key
        { "KEY_F14", 0x7D }, // F14 key
        { "KEY_F15", 0x7E }, // F15 key
        { "KEY_F16", 0x7F }, // F16 key
        { "KEY_F17", 0x80 }, // F17 key
        { "KEY_F18", 0x81 }, // F18 key
        { "KEY_F19", 0x82 }, // F19 key
        { "KEY_F20", 0x83 }, // F20 key
        { "KEY_F21", 0x84 }, // F21 key
        { "KEY_F22", 0x85 }, // F22 key
        { "KEY_F23", 0x86 }, // F23 key
        { "KEY_F24", 0x87 }, // F24 key
        { "KEY_NUMLOCK", 0x90 }, // NUM LOCK key
        { "KEY_SCROLL", 0x91 }, // SCROLL LOCK key
        { "KEY_LSHIFT", 0xA0 }, // Left SHIFT key
        { "KEY_RSHIFT", 0xA1 }, // Right SHIFT key
        { "KEY_LCONTROL", 0xA2 }, // Left CONTROL key
        { "KEY_RCONTROL", 0xA3 }, // Right CONTROL key
        { "KEY_LMENU", 0xA4 }, // Left MENU key
        { "KEY_RMENU", 0xA5 }, // Right MENU key
        { "KEY_OEM_1", 0xBA }, // for US    ";:"
        { "KEY_PLUS", 0xBB }, // Plus Key   "+"
        { "KEY_COMMA", 0xBC }, // Comma Key  ","
        { "KEY_MINUS", 0xBD }, // Minus Key  "-"
        { "KEY_PERIOD", 0xBE }, // Period Key "."
        { "KEY_OEM_2", 0xBF }, // for US    "/?"
        { "KEY_OEM_3", 0xC0 }, // for US    "`~"
        { "KEY_OEM_4", 0xDB }, // for US    "[{"
        { "KEY_OEM_5", 0xDC }, // for US    "\|"
        { "KEY_OEM_6", 0xDD }, // for US    "]}"
        { "KEY_OEM_7", 0xDE }, // for US    "'""
        { "KEY_OEM_8", 0xDF }, // None
        { "KEY_OEM_AX", 0xE1 }, // for Japan "AX"
        { "KEY_OEM_102", 0xE2 }, // "<>" or "\|"
        { "KEY_ATTN", 0xF6 }, // Attn key
        { "KEY_CRSEL", 0xF7 }, // CrSel key
        { "KEY_EXSEL", 0xF8 }, // ExSel key
        { "KEY_EREOF", 0xF9 }, // Erase EOF key
        { "KEY_PLAY", 0xFA }, // Play key
        { "KEY_ZOOM", 0xFB }, // Zoom key
        { "KEY_PA1", 0xFD }, // PA1 key
        { "KEY_OEM_CLEAR", 0xFE }, // Clear key
    };

    for (auto it = keyMapping.begin(); it != keyMapping.end(); ++it) {
        luaState.GetGlobalEnvironment().Set(it->first, it->second);
    }
}

Now we can create a Esc key handler in our script:

function handleFrame()
    -- Esc
    if KEY_STATE[KEY_ESCAPE] == true then
        exit()
    end
end

Now we are ready to create our first Newton bodies. Bodies are some invisible objects, which define how our Irrlicht meshes will behave (e. g. where they will be placed, how they will interact when moving, etc.). Basically, there are two types of bodies:

dynamic, whose movement is determined by the forces, applied to them
kinematic, which are controlled by setting their velocities

Those two kinds of bodies are totally different, so the interactions between them are not pre-defined. So when your dynamic body will fall onto a kinematic one, it will fall through.

And each body has its shape, which determines behaviour of the body, when it collides others and the collision detection itself, of course. Shapes could be convex or concave. Convex shapes are easier to work with (on the level of physics simulation), but not all the bodies in practice are convex. For example, levels are oftenly concave. So they need their special shapes, which are called Triangle Mesh.

Note: to keep the performance of your application high, try to minimalize the use of triangle meshes and use as simple shapes, as possible. Sometimes it is more effective to combine a set of primitive shapes, like spheres, cylinders and boxes into one compound shape, then to use a trimesh.

Let’s create our first simple scene, empowered with physics! We will need only two things:

a sphere
the floor

Since we do not have the good mesh in standard Irrlicht distribution for the floor (there is a Quake-like level, but that is too much for our case), we will learn how to make that simple thing in Blender. The next part is a short break between coding sessions.

Next chapter