Gamebryo Frame Rendering System Reading Notes

Let’s look into Gamebryo frame rendering system. The documentation is located in:

Gamebryo Document->Programmer Level-> Core Runtime -> Frame Rendering System

The propose of the frame rendering system is to make rendering code portable.  Applications that use the frame rendering system do all their configuration work up front. The complex effects can be performed automatically at render time.

Render Frame(NiRenderFrame) represents an entire rendering process. It must be set up during initialization and displayed each frame. It has many render steps and iterates through the rend steps telling them to hook callback function to a frame.

Render Step(NiRenderStep) is a single rendering effect. It does the actual rendering work. It can be turned on/off to control the final effect. One Rend Step usually performs one or more rendering passes via render click objects.

Render Click(NiClickRenderStep) is a complete rendering pass. It can be easily enabled or disabled by 1) application in every frame 2) a render click validator according to some criteria. 3) pre/post callback function.

Render View(NiRenderView) objects provide a certain type of render click with an array of geometry to render. They can do this by culling a scene graph against a camera or by using some other algorithm to determine which geometry objects need to be rendered.

Render List Processor(NiRenderListProcessor) ,During rendering, the processor is passed an array of geometry objects that need to be rendered and passes back an array of objects that still need to be rendered. By controlling that output array, the render list processor can modify the geometry array, such as rendering some geometry objects immediately and deferring rendering of a sorted list for later.

GameBryo Asset Service and Actionmap

GameBryo Asset Service provides an easy way to access game data. For all the assets( Entity models, logic scripts,images etc), the asset service assigns a unique name to each of them.  The unique id is called Uniform Resource Identifier (URI) that is prefixed by the string “urn:”, followed by one or more specifiers.

Examples:

• urn:gamebryo-scenegraph:Precache—All assets that are tagged with both “gamebryo-scenegraph” and “Precache”, which might be used to identify every asset that should be pre-loaded during application startup.
• urn:emergent-world:Level1—An asset that is tagged with “emergent-world” and has the name of “Level1″, which might be used to load all the entities needed in the first level of a game.
• urn:llid:0716a14d-81ca-46f2-9e7e-7dc30ff2c561:Wii—A logical asset with the indicated unique ID and also tagged “Wii”, which might be used to load the Wii variation of an asset selected with an asset-picker in a tool.

Assets in Hello World Demo:

In the hello world example, the HelloWorldService::SetupInputActions() function uses “urn:gamebryo-actionmap:HelloWorldActionMap” to load a key-action map. It maps the “m” key to HELLOWROLD_ACTION_DROP event and “n” key to HELLOWORLD_ACTION_PICKUP event. The  actionmap file is located in \Gamebryo\Media\Samples\GameFramework\HelloWorld\HelloWroldActionMap.actionmap.

Also, in ConfigCommon.ini file, the initial world is specified by

[Game]
InitialWorld = urn:emergent-world:HelloWorld

The question is how does gamebryo map URN  to  file. This question is very important because you must understand the asset service in order to use assets.

Let’s take a close look on HelloWrold cpp project.

In Config.ini file, we have an attribute

[AssetWeb.Win32]
Path=$(SourceBaseDir)/../../../Media

This attribute specifies the root directory for Asset directory. The config manager service will load this attribute in run time. On my computer, the AssetWeb root folder is F:\Gamebryo\Media. There are three files in Media/asset-web-config directory which define the asset web.

The LogicalIdTagger.ini defines some logical tags:

; The Assets are a list of asset types (assigned by the MimeTagger) that should have logical
; asset id’s assigned to them. If the asset does not possess one of these tags, then no logical
; asset id is created for it.  Logical asset id’s are only needed for assets that will be referenced
; by other asset files, like block or model files.
[LogicalIdTagger.Assets]
=gamebryo-scenegraph
=gamebryo-animation
=gamebryo-terrain
=gamebryo-terrain-materialpkg
=physx-terrain
=gamebryo-actionmap
=wwise-sound-bank
=bmp-image

In MimeTagger.ini, for each file extension, a pair of tags is created from the associated MIME  type.  For example, “py=script/python-behavior” will result in every file
with the “.py” extension having two tag values – “script” and “python- behavior”.

xblock=x-world/emergent-world

kf=application/gamebryo-sequence-file
actionmap=application/gamebryo-actionmap
bnk=audio/wwise-sound-bank

Therefore, HelloWorldActionMap.actionmap file is named as “urn:gamebryo-actionmap:HelloWorldActionMap” and the HelloWrold.xblock is named as “urn:emergent-world:HelloWorld”.  The path of those files are irrlevent to urn.  The asset service searches all the sub directories under AssetWeb root and classifies files accordingly.

Key Actionmap

The Hello World example demonstrates two ways of handling key event.

1. Register a key handler function and switch the logic according to key code.

EE_HANDLER(HelloWorldService, HandleKeyDownMessage, KeyDownMessage); // Register handler

void HelloWorldService::HandleKeyUpMessage(const KeyUpMessage *pMessage,
 efd::Category targetChannel)
{
 Entity* pAvatar = GetAvatar();
 if (pAvatar)
 {
 switch (pMessage->GetKey()) // Switch key code
 {
 case NiInputKeyboard::KEY_UP:
 pAvatar->SetPropertyValue("IsMoving", false);
 break;

 case NiInputKeyboard::KEY_LEFT:
 pAvatar->SetPropertyValue("IsTurningLeft", false);
 break;

...

2. Use a data-driven actionmap to bind keys to events. Currently, there’s no tool to help you generate actionmap  file; therefore, you need to edit the file by hand. Please read the The ecrInput Library documentation for detail.

HelloWorldActionMap.actionmap
...
 <Event EventName="HELLOWORLD_ACTION_DROP" EventCategory="0xC000000007765433" EventFlags="RETURN_MAGNITUDE">
 <ActionsList>
 <!--Flags - InputService.h ActionFlags enum - use individual string values or combined bitmask as an int-->
 <!--DeviceID - a way to define action for specific controllers-->
 <!--Modifiers - NiInputKeyboard Modifiers enum-->
 <!--ActionClsID - (ACTION/DPAD/STICK)-->
 <!--Semantic - NiAction.h Semantic enum for gpad string values GP_BUTTON_LUP or NiInputKeyboard.h for key value strings KEY_M, etc-->
 <Action Flags="ON_ACTIVATE" DeviceID="0" Modifiers="0" ActionClsID="ACTION" Semantic="KEY_M"MinRange="-1.000000" MaxRange="1.000000" />
 <Action Flags="ON_ACTIVATE" DeviceID="0" Modifiers="0" ActionClsID="ACTION" Semantic="GP_BUTTON_RDOWN" MinRange="-1.000000" MaxRange="1.000000" />
 </ActionsList>
 </Event>
 <!--0xC000000007765432-->
 <!--13835058055407359026-->
 <Event EventName="HELLOWORLD_ACTION_PICKUP" EventCategory="0xC000000007765432" EventFlags="RETURN_MAGNITUDE">
 <ActionsList>
 <Action Flags="ON_ACTIVATE" DeviceID="0" Modifiers="0" ActionClsID="ACTION" Semantic="KEY_N" MinRange="-1.000000" MaxRange="1.000000" />
 <Action Flags="ON_ACTIVATE" DeviceID="0" Modifiers="0" ActionClsID="ACTION" Semantic="GP_BUTTON_RRIGHT" MinRange="-1.000000" MaxRange="1.000000" />

After you create the actionmap, you can create an action message handler.

// Define the message categories for the actions
static const efd::Category kCAT_STANDALONE_ACTION_PICKUP =
 Category( efd::UniversalID::ECU_Any, 0, 0x07765432 );

static const efd::Category kCAT_STANDALONE_ACTION_DROP =
 Category( efd::UniversalID::ECU_Any, 0, 0x07765433 );

...

void HelloWorldService::HandleActionMessage(const InputActionMessage* pMsg,
 efd::Category targetChannel)
{
 Entity* pAvatar = GetAvatar();

 switch(pMsg->GetClassID())
 {
 case efd::kMSGID_CoreInputAction:
 if (pAvatar)
 {
 if(targetChannel == kCAT_STANDALONE_ACTION_PICKUP)
 {
 pAvatar->SendEvent(pAvatar->GetEntityID(), "Jack", "PickupEntity");
 }
 else if(targetChannel == kCAT_STANDALONE_ACTION_DROP)
 {
 pAvatar->SendEvent(pAvatar->GetEntityID(), "Jack", "DropEntity");
 }
 }
 break;
 }

}

Reference:

Gamebryo Documentation: Programmer Level->Foundation->Asset Runtime Service

Gamebryo Documentation: The ecrInput Library

HelloWorld example project

Gamebryo weekly notes

Weekly Goals Sept 24 to Oct 1 .

1. Write a class to represent/display dynamic string in GameBryo.

Relevant class: Ni2DString, NiString, NiFont etc.

Nots: Ni2DString::Draw()  Draw the string. This call must appear between a call to NiRenderer::BeginUsingRenderTargetGroup and a subsequent call to NiRenderer::EndUsingRenderTargetGroup.

Possible Solution: Edit InputDemo and replace the dynamic string funtions in InputDemo.

2. Add game state in MOUT demo

Right now, the MOUT demo doesn’t support state change. After I finish the dynamic string. I need to add it to MOUT. When player hits ENTER, the game changes to INPUT_STATE and player could type. When the player hits ESC key, the game return to CONTROL_STATE and player could control the movment of soldier.

Questions

1. Gamebryo doesn’t not support UNICODE for the engine.

Furthermore, builds of Gamebryo with UNICODE or _UNICODE defined are not supported.

Check my VS2008 solution setting.

Weekly Goals Oct 4to Oct 11 .

1. Read the CEGUI intergration source code to find out how to create/add/remove UI item

2. Create my GUI according to the tutorial and load the gui into integration demo

3. Fix the bugs in message service.

4. Complete read the current Londontown source along with relative Gamebryo documentation. Especially for 3d engine part

Oct 11 – Oct 31

Solve the memory leak problem in CEGUI integration

Wrote a simple tic tac toe game in lightspeed

Wrote chatting system in integration project

Port the chatting system to London Town project

Weekly Achievements.

Nov 1-7

Finished the chatting system.

Resize the chat window

Add line warpping function

Leaned how to switch scheme

Nov 8-14

Read the NiPick document

Pick object from London town