Tech Talk: Tech Talk: DirectDrawDirectDraw

Alex RiemannAlex RiemannUniversity of Illinois, University of Illinois, Urbana-ChampaignUrbana-Champaign

February 13, 2000February 13, 2000

Graphics Programming in Graphics Programming in DOSDOS

Very Limited Video HardwareVery Limited Video Hardware Required the developer to know Required the developer to know

what features the video hardware what features the video hardware providedprovided

Video Electronics Standards Video Electronics Standards Association (VESA)Association (VESA) Helped relieve this situationHelped relieve this situation Provided semi-common interface to Provided semi-common interface to

video memoryvideo memory

Graphics Programming in Graphics Programming in WindowsWindows

Common set of API’s to access graphics Common set of API’s to access graphics subsystemsubsystem

Numerous layers of indirection between Numerous layers of indirection between the programmer and the hardwarethe programmer and the hardware

Graphics Device Interface (GDI) objectsGraphics Device Interface (GDI) objects Great for Circles, Squares, and other simple Great for Circles, Squares, and other simple

objectsobjects Far too slow to handle effects for video Far too slow to handle effects for video

games!games!

Enter the Game SDKEnter the Game SDK

Introduced to promote game Introduced to promote game development on the Windows development on the Windows PlatformPlatform

Designed to shift responsibility Designed to shift responsibility away from the developer and to the away from the developer and to the hardware manufacturerhardware manufacturer

Soon became known as DirectXSoon became known as DirectX

What does DirectX What does DirectX provide?provide?

Fast, low latency access to hardwareFast, low latency access to hardware Hardware emulation for certain tasks (if Hardware emulation for certain tasks (if

required)required) A single set of API calls regardless of A single set of API calls regardless of

system hardwaresystem hardware Multiplayer support that is indifferent to Multiplayer support that is indifferent to

transport media (TCP/IP, IPX, Null Modem, transport media (TCP/IP, IPX, Null Modem, etc.)etc.)

And so much more!And so much more!

The Hardware Abstraction The Hardware Abstraction Layer (HAL)Layer (HAL)

Standard interface to any Standard interface to any hardware device supported by hardware device supported by Windows and DirectXWindows and DirectX

The HAL is a very thin software The HAL is a very thin software layer provided by the vendor to layer provided by the vendor to interface with the hardware deviceinterface with the hardware device

The Hardware Emulation The Hardware Emulation Layer (HEL)Layer (HEL)

Used to provide those functions in Used to provide those functions in software that are not available in software that are not available in hardwarehardware

A much slower solution, however it A much slower solution, however it allows all systems to provide at allows all systems to provide at least a minimal amount of DirectX least a minimal amount of DirectX functionalityfunctionality

Components of DirectXComponents of DirectX

DirectDrawDirectDraw Direct3DDirect3D DirectSoundDirectSound DirectPlayDirectPlay DirectInputDirectInput DirectSetupDirectSetup DirectMusicDirectMusic DirectShowDirectShow

DirectDraw BasicsDirectDraw Basics

Provides an interface to the 2D Provides an interface to the 2D hardware available on modern hardware available on modern video cardsvideo cards

Important ConceptsImportant Concepts Graphics ModesGraphics Modes The DirectDraw ObjectThe DirectDraw Object Primary DirectDraw SurfacePrimary DirectDraw Surface

Data Structure Data Structure InitializationInitialization

Critical in DirectXCritical in DirectX ExampleExample

Typically, DirectX structures require Typically, DirectX structures require that the dwSize parameter be initializedthat the dwSize parameter be initialized

DDSURFACEDESC ddsdesc;

ZeroMemory(&ddsdesc, sizeof(ddsdesc));

ddsdesc.dwSize = sizeof(ddsdesc);

Page FlippingPage Flipping

Requires addition of a Back Buffer Requires addition of a Back Buffer SurfaceSurface

Prevents “tearing” from occurringPrevents “tearing” from occurring

No Page Flipping Demo

Page Flipping Demo

Page Flipping – IllustrationPage Flipping – Illustration

Surface 1

Surface 2

Before Page Flip

DisplayAddress Front

Buffer

BackBuffer

Monitor

Surface 1

Surface 2

After Page Flip

DisplayAddress Front

Buffer

BackBuffer

Monitor

The SurfaceThe Surface

Typically “imagined” as a 2D surface, Typically “imagined” as a 2D surface, however is actually a linear bufferhowever is actually a linear buffer

Described by the DDSurfaceDesc Described by the DDSurfaceDesc structurestructure A DDSURFACEDESC structure is used to A DDSURFACEDESC structure is used to

either define a surface when either define a surface when CreateSurface is called or to describe CreateSurface is called or to describe the current condition of a buffer using the current condition of a buffer using GetSurfaceDescGetSurfaceDesc

MSDN – Your FriendMSDN – Your Friend

Exercise – Look up DDSurfaceDesc Exercise – Look up DDSurfaceDesc and read the description of its and read the description of its member variablesmember variables

Launch MSDNLaunch MSDN Important Member VariablesImportant Member Variables

PitchPitch lpSurfacelpSurface ddckCKDestBlt, ddckCKSrcBltddckCKDestBlt, ddckCKSrcBlt

Blitting to a SurfaceBlitting to a Surface

A blit is the process of copying an A blit is the process of copying an image from one surface onto image from one surface onto anotheranother

Two Types of blitting in DirectDrawTwo Types of blitting in DirectDraw Direct access of the surface to Direct access of the surface to

perform the blitperform the blit Using Blt and BltFast to perform the Using Blt and BltFast to perform the

blitting operationblitting operation

Blt and BltFastBlt and BltFast

Used to fill surfaces or copy an Used to fill surfaces or copy an image to a surfaceimage to a surface

BltFast has less options than BltBltFast has less options than Blt BltFast provides a speed increase BltFast provides a speed increase

when the HEL is being used (~10%)when the HEL is being used (~10%) Blt DemoBlt Demo

But I don’t want to have only But I don’t want to have only squares!squares!

Loading Images into an Off-Screen SurfaceLoading Images into an Off-Screen Surface Typically requires direct access of the screen Typically requires direct access of the screen

buffer to allow for custom file formatsbuffer to allow for custom file formats Raw 24bpp images require no decompression, Raw 24bpp images require no decompression,

however they are largehowever they are large Bitmaps can be blitted through the GDIBitmaps can be blitted through the GDI The Lock() and Unlock() functionsThe Lock() and Unlock() functions

Used to “grab” a surface to blt toUsed to “grab” a surface to blt to Must be used together or other functions will be Must be used together or other functions will be

unable to access the surface!unable to access the surface!

File I/OFile I/O

CreateFile, ReadFile, CloseHandleCreateFile, ReadFile, CloseHandle CreateFile returns a handle to a new or existing CreateFile returns a handle to a new or existing

file so read/write operations can occurfile so read/write operations can occur ReadFile returns a specified number of bytesReadFile returns a specified number of bytes CloseHandle closes the fileCloseHandle closes the file

Transparent BltsTransparent Blts

DDCOLORKEY StructureDDCOLORKEY Structure Two member variables used to define a color Two member variables used to define a color

space that will appear transparentspace that will appear transparent Select the color key for a surface using Select the color key for a surface using

the SetColorKey() Methodthe SetColorKey() Method Select either the Destination Color Key or Select either the Destination Color Key or

the Source Color Keythe Source Color Key Call Blt or BltFast using the appropriate Call Blt or BltFast using the appropriate

flag to create the transparent Bltflag to create the transparent Blt

Transparent Blt DemoTransparent Blt Demo

DemoDemo The selected color key is The selected color key is

RGB(255,0,255) – the pink in this RGB(255,0,255) – the pink in this picturepicture

Interfacing to the UserInterfacing to the User

Win32 MessagesWin32 Messages WM_MOUSEMOVE, WM_LBUTTONDOWN, etc.WM_MOUSEMOVE, WM_LBUTTONDOWN, etc. Excellent for applicationsExcellent for applications Dependent upon message queue to handle Dependent upon message queue to handle

user inputuser input Direct InputDirect Input

Requires polling of the deviceRequires polling of the device Can be synced to get new input every frameCan be synced to get new input every frame Allows use of specialized game devicesAllows use of specialized game devices

USB Joysticks, Flight Pedals, etc.USB Joysticks, Flight Pedals, etc.

Direct InputDirect Input

USB ConsiderationsUSB Considerations USB allows for up to 127 devices to USB allows for up to 127 devices to

be connected!be connected! The user may have more than one The user may have more than one

mouse, joystick or keyboard mouse, joystick or keyboard connected to the systemconnected to the system

Needs to “gracefully” recover from Needs to “gracefully” recover from having a device disconnected from having a device disconnected from the systemthe system

Multi-Threaded Application Multi-Threaded Application DevelopmentDevelopment

Threads rock!Threads rock! Every programmer loves threads the Every programmer loves threads the

first time they use themfirst time they use them A multi-threaded application can A multi-threaded application can

perform multiple tasks at “once”perform multiple tasks at “once” Very useful to allow GUIs to appear Very useful to allow GUIs to appear

“alive” as an intensive calculation “alive” as an intensive calculation occurs in the backgroundoccurs in the background

Multi-Threaded DemoMulti-Threaded Demo

Thread SynchronizationThread Synchronization

Critical SectionsCritical Sections Kernel ObjectsKernel Objects

Ex. Mutex, Semaphore, Event, Ex. Mutex, Semaphore, Event, Thread, Process and many moreThread, Process and many more

Critical SectionCritical Section

A segment of code that needs to be A segment of code that needs to be executed without being pre-emptedexecuted without being pre-empted

Started by making a call to Started by making a call to EnterCriticalSectionEnterCriticalSection

Completed by calling LeaveCriticalSectionCompleted by calling LeaveCriticalSection System will appear “locked” during a critical System will appear “locked” during a critical

sectionsection Important to keep these sections to a minimal Important to keep these sections to a minimal

sizesize Only use in areas that require it to be usedOnly use in areas that require it to be used

Kernel ObjectsKernel Objects An object that is shared between An object that is shared between

threadsthreads WaitForSingleObject and WaitForSingleObject and

WaitForMultipleObject will wait until WaitForMultipleObject will wait until a specified kernel object is signaleda specified kernel object is signaled Important to thoroughly analyze the Important to thoroughly analyze the

return value to prevent from return value to prevent from misinterpreting the resultsmisinterpreting the results

WAIT_FAILED, WAIT_OBJECT_0, WAIT_FAILED, WAIT_OBJECT_0, WAIT_TIMEOUT, WAIT_ABANDONED_0WAIT_TIMEOUT, WAIT_ABANDONED_0

Example – Buggy CodeExample – Buggy Code

DWORD dwWaitResult;

dwWaitResult = WaitForSingleObject(hMutex, 1000);

If (WAIT_FAILED == dwWaitResult)

{ // Handle Failure }

Else

{ // Assume Success – Potential Bug! }

Example – Solid CodeExample – Solid Code

DWORD dwWaitResult;

dwWaitResult = WaitForSingleObject(hMutex, 1000);

If (WAIT_OBJECT_0 == dwWaitResult)

{ // The mutex is now owned }

Else

{ // Handle Wait failure. Differentiate between the 3 possible failures }

Dangers of Multi-Threaded Dangers of Multi-Threaded DevelopmentDevelopment

““Dueling” conditions between Dueling” conditions between threadsthreads Race ConditionsRace Conditions

Exist where two or more threads are Exist where two or more threads are competing to share the same resourcecompeting to share the same resource

Very difficult to track – good design will Very difficult to track – good design will prevent bugs of this natureprevent bugs of this nature

StarvationStarvation Occurs when a single thread controls a Occurs when a single thread controls a

resource due to scheduling priorityresource due to scheduling priority

Race Condition ExampleRace Condition Example

Two threads A and B share a Two threads A and B share a common DirectDraw Surfacecommon DirectDraw Surface

Thread A locks the surfaceThread A locks the surface Before it is unlocked, A is pre-Before it is unlocked, A is pre-

empted by B, which needs to access empted by B, which needs to access the surfacethe surface

Solution: Use a critical section to Solution: Use a critical section to prevent a conflict or consolidate the prevent a conflict or consolidate the two threadstwo threads

Starvation ExampleStarvation Example

Two threads – A and BTwo threads – A and B A has higher priority than BA has higher priority than B They share a common resourceThey share a common resource A completes so quickly that it A completes so quickly that it

immediately reacquires the immediately reacquires the resource preventing B from resource preventing B from executingexecuting

Application to Game Application to Game DevelopmentDevelopment

Allows background processing of dataAllows background processing of data Example:Example:

One thread for system messagesOne thread for system messages One thread for drawing the frame bufferOne thread for drawing the frame buffer One thread to handle input (user or network)One thread to handle input (user or network)

Potential increase in speed by using Potential increase in speed by using multiprocessor systemsmultiprocessor systems Quake 3Quake 3

Basics to start Basics to start programmingprogramming

The latest DirectX SDKThe latest DirectX SDK Make sure to add ddraw.lib to the Make sure to add ddraw.lib to the

link option in Visual C++ (under link option in Visual C++ (under the Project->Settings menu)the Project->Settings menu)

Have patience! Debugging Have patience! Debugging DirectDraw is difficultDirectDraw is difficult

MSDNMSDN

Further ReadingFurther Reading

Inside DirectXInside DirectX, Bargen and , Bargen and Donnelly. Microsoft PressDonnelly. Microsoft Press

Win32 Multithreaded ProgrammingWin32 Multithreaded Programming, , Cohen and Woodring. O’Reilly.Cohen and Woodring. O’Reilly.

Programming WindowsProgramming Windows, Charles , Charles Petzold. Microsoft Press. (No Petzold. Microsoft Press. (No Windows programmer should be Windows programmer should be without this!)without this!)

ContactsContacts

Alex RiemannAlex Riemann Riemann@uiuc.eduRiemann@uiuc.edu

Microsoft UIUC Recruiter - Tracy Microsoft UIUC Recruiter - Tracy FoltzFoltz Tracyfo@microsoft.comTracyfo@microsoft.com