SDL Programming

Introduction

2

Initialization The first thing you must do is initialize SDL

int SDL_Init( SDL_INIT_EVERYTHING ) This will return -1 if it fails Various flags can be OR’ed together to enable various

features In this case, we enable all features

3

Surfaces A surface is an area where you can draw The screen is one such surface You can create other surfaces to hold images

or to draw on You can copy one surface to another Surfaces have properties

Height Width Number of bits per pixel

4

Creating the Screen After initializing SDL, you create the screen

SDL_Surface *screen; screen = SDL_SetVideoMode(

winWidth, winHeight, screenDepth, SDL_HWSURFACE | SDL_DOUBLEBUF);

The screen depth is usually 32 If the screen cannot be created, NULL will be

returned When a surface is no longer needed it should

be freed SDL_FreeSurface(surface);

5

Setting a Window Title You can set the title in the top of the window

SDL_WM_SetCaption( “Title", NULL );

The title will be displayed in the window decoration area, usually at the top of the window

6

SDL Coordinates

(0, 0)(100, 0)

(0, 100) (100, 100)

•The origin of a window is the top-left corner•Y coordinates increase as we go down

7

Loading Images SDL can load images in the BMP format There are extensions which can load other

formats These extensions must be downloaded and

installed into your SDL directories Loaded images are stored on surfaces Remember, the screen itself is a surface You can then copy them from one surface to

another to make them appear on the screen

8

Loading Images To load an image

SDL_Surface *image = SDL_LoadBMP(“file.bmp”); This will either load the image or return NULL if it

cannot be loaded

The trouble is that the image might not have the same format as the screen you want to display it on

You can convert it to the correct format as follows SDL_Surface *displayImage =

SDL_DisplayFormat(image);

9

Loading Images These steps are done often enough to warrant

creating a function or method for loading an image

SDL_Surface* loadImage(const char* fileName) {SDL_Surface *tmp = NULL, *image = NULL;tmp = SDL_LoadBMP(fileName);if(tmp) {

image = SDL_DisplayFormat(tmp);SDL_FreeSurface(tmp);

}return image;

}

10

Rendering Images When you load an image

It is stored on a surface This does not make the image visible

The image must be copied to the screen to be visible

We move an image using bit blitting Bit block image transfer This is done with the function SDL_BlitSurface

11

SDL_BlitSurface int SDL_BlitSurface(

SDL_Surface *src, SDL_Rect *srcrect, SDL_Surface *dst, SDL_Rect *dstrect)

Src – source surface Srcrect – rectangle delimiting areas to copy or NULL

for entire image Dst – the destination surface Dstrect – position to place on destination surface. If

NULL image will be placed at top-left corner Returns 0 on success

12

SDL_Rect This is a common structure used to indicate

the size and position of rectangular areas

typedef struct{ Sint16 x, y; Uint16 w, h;

} SDL_Rect;

13

Event Handling Many events happen while a program is

running Key presses Mouse movement Window resizing Window closing

Games are interested in these events and need to be able to find out when they occur

This can be done using SDL_PollEvent(& event)

14

SDL_Event

typedef union{ Uint8 type; SDL_ActiveEvent active; SDL_KeyboardEvent key; SDL_MouseMotionEvent motion;

SDL_MouseButtonEvent button; SDL_JoyAxisEvent jaxis; SDL_JoyBallEvent jball; SDL_JoyHatEvent jhat; SDL_JoyButtonEvent jbutton; SDL_ResizeEvent resize; SDL_ExposeEvent expose; SDL_QuitEvent quit; SDL_UserEvent user; SDL_SysWMEvent syswm; } SDL_Event;

• This is used for all event types• Note that it is a union• The type field indicates which member of the union is to be used

15

SDL Event Types & StructuresEvent type Event Structure

SDL_ACTIVEEVENT SDL_ActiveEvent

SDL_KEYDOWN/UP SDL_KeyboardEvent

SDL_MOUSEMOTION SDL_MouseMotionEvent

SDL_MOUSEBUTTONDOWN/UP SDL_MouseButtonEvent

SDL_JOYAXISMOTION SDL_JoyAxisEvent

SDL_JOYBALLMOTION SDL_JoyBallEvent

SDL_JOYHATMOTION SDL_JoyHatEvent

SDL_JOYBUTTONDOWN/UP SDL_JoyButtonEvent

SDL_VIDEORESIZE SDL_ResizeEvent

SDL_VIDEOEXPOSE SDL_ExposeEvent

SDL_QUIT SDL_QuitEvent

SDL_USEREVENT SDL_UserEvent

SDL_SYSWMEVENT SDL_SysWMEvent

16

SDL_KeyboardEvent

typedef struct{ Uint8 type; Uint8 state; SDL_keysym keysym; } SDL_KeyboardEvent;

Field Values Description

type SDL_KEYDOWNSDL_KEYUP

Type of key event

State SDL_KEYPRESSEDSDL_KEYRELEASED

Same as type

keysym Structure The key pressed

17

SDL_keysym

typedef struct{ Uint8 scancode; SDLKey sym; SDLMod mod; Uint16 unicode; } SDL_keysym;

Field Values Description

scancode Hardware scan code

sym See table SDL virtual key code

mod Key modifiers

unicode Translated character

18

SDL Key SymbolsSDL key ASCII Name

SDLK_BACKSPACE '\b' backspac

e

SDLK_TAB '\t' tab

SDLK_CLEAR clear

SDLK_RETURN '\r' return

SDLK_PAUSE pause

SDLK_ESCAPE '^[' escape

SDLK_SPACE ' ' space

SDLK_EXCLAIM '!' exclamation

SDLK_QUOTEDBL '"' double

quote

SDLK_HASH '#' hash

SDLK_DOLLAR '$' dollar

SDLK_AMPERSAND '&' ampersa

nd

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SDL Key SymbolsSDL key ASCII Name

SDLK_QUOTE '\'' single quote

SDLK_LEFTPAREN '(' left

parenthesis

SDLK_RIGHTPAREN ')' right

parenthesis

SDLK_ASTERISK '*' asterisk

SDLK_PLUS '+' plus sign

SDLK_COMMA ',' comma

SDLK_MINUS '-' minus sign

SDLK_PERIOD '.' period / full stop

SDLK_SLASH '/' forward slash

SDLK_COLON ':' colon

SDLK_SEMICOLON ';' semicolon

SDLK_LESS '<' less-than sign

20

SDL Key SymbolsSDL key ASCI

IName

SDLK_EQUALS '=' equals sign

SDLK_GREATER '>' greater-than sign

SDLK_QUESTION '?' question mark

SDLK_AT '@' at

SDLK_LEFTBRACKET '[' left bracket

SDLK_BACKSLASH '\\' backslash

SDLK_RIGHTBRACKET ']' right bracket

SDLK_CARET '^' caret

SDLK_UNDERSCORE '_' underscore

SDLK_DELETE '^?' delete

SDLK_UP up arrow

SDLK_DOWN down arrow

21

SDL Key SymbolsSDL key ASCII Name

SDLK_RIGHT right arrow

SDLK_LEFT left arrow

SDLK_INSERT insert

SDLK_HOME home

SDLK_END end

SDLK_PAGEUP page up

SDLK_PAGEDOWN page down

SDLK_F1 ... F1

SDLK_F15 F15

SDLK_PRINT print-screen

SDLK_SYSREQ SysRq

SDLK_BREAK break

22

SDL Key Symbols

SDL key ASCII Name

SDLK_0 '0' 0

SDLK_1 '1' 1

SDLK_2 '2' 2

SDLK_3 '3' 3

SDLK_4 '4' 4

SDLK_5 '5' 5

SDLK_6 '6' 6

SDLK_7 '7' 7

SDLK_8 '8' 8

SDLK_9 '9' 9

23

SDL Key SymbolsSDL key ASCII

SDLK_a 'a'

SDLK_b 'b'

SDLK_c 'c'

SDLK_d 'd'

SDLK_e 'e'

SDLK_f 'f'

SDLK_g 'g'

SDLK_h 'h'

SDLK_i 'i'

SDLK_j 'j'

SDLK_k 'k'

SDLK_l 'l'

SDLK_m 'm'

SDL key ASCII

SDLK_n 'n'

SDLK_o 'o'

SDLK_p 'p'

SDLK_q 'q'

SDLK_r 'r'

SDLK_s 's'

SDLK_t 't'

SDLK_u 'u'

SDLK_v 'v'

SDLK_w 'w'

SDLK_x 'x'

SDLK_y 'y'

SDLK_z 'z'

24

Event Processing Loop

while(SDL_PollEvent(&event)){ switch(event.type){ case SDL_KEYDOWN: if(event.key.keysym.sym==SDLK_LEFT) move_left(); break; . . . } }Poll for events and process each of

the events

25

The Game Loop

bool quit = false;SDL_Event event;

while( quit == false ) { if( SDL_PollEvent( &event ) ) { if( event.type == SDL_QUIT ) { quit = true; } if( SDL_Flip( screen ) == -1 ) {

//return 1; } }}

This processes eventsand keeps the windowon the screen untilthe X in the top rightof the window is clicked.

26

Drawing Text SDL does not support TTF fonts as distributed You can download the extension from

http://www.libsdl.org/projects/SDL_ttf/ Get the file

SDL_ttf-devel-2.0.10-VC.zip Open the zip file and

Copy the file in include to the include directory for your SDL

Copy the files in lib to the lib directory for your SDL

You will need to copy the new DLLs to any project that wants to use text

27

Preparing to Use Text Set the text color

SDL_Color textColor;textColor.r = textColor.g = textColor.b = 255;

Initialize the TTF extensionif( TTF_Init() == -1 ) { return false; }

Load the fontif( NULL == (font = TTF_OpenFont( "lazy.ttf", 28 )) )

{ return false; }

28

Rendering the Text text is rendered to a newly created surface You then copy this surface onto the surface

where the text should appear

textSurface = TTF_RenderText_Solid( font, "A-Maze-ing", textColor );

This surface is then blitted onto the destination surface

29

Colors Colors are specified as

RGB with each value from 0 – 255 There are two different structures

An unsigned 32 bit int An SDL_Color structure

SDL_Color has members r, g, b

To create the 32 bit intunsigned int color = SD_MapRGB(screen->format,

255, 255, 255);

30

Drawing Lines & Rectanglesint SDL_DrawLine(SDL_Surface* dst,

int x1, int y1, int x2, int y2, Uint32 color)

int SDL_FillRect(SDL_Surface *dst, SDL_Rect *dstrect, Uint32 color)

Both functions return 0 on success