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Introduction to SDL
 Initializing the SDL

SDL is made up of subsystems:video, audio, timing… You can initialize some

components by specifying their names or initialize all the components using the
“EVERYTHING” flag

- - > Initializationis ensured thanks to the functionSDL_Initwhich returns 0 if the

initialization was successful.
before retrieving the number before playing
Example : before displaying
of seconds since initialization a sound
a picture
of SDL

SDL_Quit(): allows you to release resources used by already initialized SDL

subsystems.
 Creating a window
SDL_SetVideoMode(width, height, number of displayable colors, flags);
allows you to create a window whose width, height and resolution (in pixels) are changed to
settings.
Flags

Example :
SDL_SetVideoMode (400,400,32, SDL_HWSURFACE | SDL_DOUBLEBUF);

Resolution Examples
 SDL_SetVideoMode flags

SDL_SWSURFACE:Saving data in RAM

SDL_HWSURFACE:Saving data in the graphics card's video memory (VRAM)

SDL_RESIZABLE:Enlarge/shrink a window

SDL_DOUBLEBUf:technique allowing smooth movement of objects

 Show an image

Ifyou manipulate .bmp images, you can make do with the bibSDL.h Otherwise,
you must include the library:SDL_image.h
# include <SDL/SDL_image.h>

❖ Declaration of a surface ²²
SDL_Surface *image;

❖ Loading an image into a surface

image=IMG_Load(filename); // for any type of images image=
SDL_LoadBMP(filename);// only for bitmap images
 Scale / Mark in an SDL Surface

Whether the surface is a screen or an image an SDL mark is represented as follows:

(0,0)
X

Y
 The SDL_Rect type

The typeSDL_Rectdefines a rectangular area. It is used by SDL_BlitSurface()

to define paste regions.

This is a predefined structure in the SDL.h library. This structure is made up of the
following fields:

- x: the abscissa
- y: the ordinate
- w: width
- h: height
 Show an image
❖ To paste an image on a screen we use the function:
The source surface to copy The region The destination surface: Screen
source
SDL_BlitSurface(SDL_Surface* src, const SDL_Rect* srcrect, SDL_Surface* dst, SDL_Rect* dstrect)

The destination location

srcrect: the value of this field is:
- NULL: if you want to display the entire image
- address of an SDL_Rect type variable: if you want to display part of the image. dstrect:the
value of this field is equal to the address of a pos position declared and initialized previously.

❖ Screen update:
Screen refresh involves refreshing the screen after making multiple pastes
SDL_Flip(SDL_Surface *screen);
Example: display the background image and the second image of
Neymar

position of the image

relative to the screen

what part of the image

should be displayed

image.h image.c 9
Example: display e of
Neymar

main.c
10
Example: display the background image and the second image of
Neymar

position of the image

relative to the screen

what part of the image

should be displayed

image.h image.c 11
Example: display the background image and the second image of
Neymar

main.c
12
 Show text
A text is a surface designed from a character string, a color, a font and a size.

To create a text, you must include the library<SDL/SDL_ttf.h>and follow the following
steps:
1.Initializing SDL_ttf:TTF_Init();

2. Loading a font and initializing the size

TTF_Font *font =TTF_OpenFont(font file, Size);
Example :
font = TTF_OpenFont("times.ttf", 65);

1. color initialization
SDL_Color textColor=(R,G,B); the value of R, J, B must be between 0 and
255 For more information on color codes consultthis palette .
Display text: example of color codes
 Display text: Fonts

● On Ubuntu, you already have several fonts (files with .ttf extension)
under this directory: /usr/share/fonts/truetype

● If you want to use

example ofThis site .
 Show text
3. Writing methods:
TTF_RenderText_Solid; if you have text that changes often.
TTF_RenderText_Shaded;if your text doesn't change very often and you want to blister your text on a plain background.

TTF_RenderText_Blended;if your text doesn't change very often but you want to blister on a non-solid
background (like an image).

Example of writing text in Blended:

SDL_Surface *text = NULL; Loading the font The message to be displayed Thisorol of the message
SDL_Color black color={0, 0, 0};
text=TTF_RenderText_Blended(police , " Message " , black color );

4. Bliter the surface:SDL_BlitSurface (text, NULL, screen, &positionScreen);

5. Close the font:TTF_CloseFont(font);

6. Stopping SDL_ttf:TTF_Quit();
Example: display the text Neymar in yellow at pos(300, 50)

text.h text.c 17
Example: display 00, 50)

main.c
18
 Play continuous sound
SDL_mixer:
•Sound mixing library.
•Allows audio management.
1. Initialize SDL_mixer audio functions:
output lozn
Efcohrm frequencyanattildlo'éncnhaagnet(iH) Bytes/sample

intMix_OpenAudio(intfrequency, Uint16format, intchannels, intchunk size);

Number of sound channels
2. Loading music:
Mix_Music *music;
music =Mix_LoadMUS("music.mp3");
3. Play the music
Number of repetitions (-1 infinity)

intMix_PlayMusic(Mix_Music *music, int loops);

4. Liberation of music
Mix_FreeMusic(music);
19
 Play continuous sound

Example:

20
 Play a short sound

1. Loading sound effects:

Mix_Chunk*her;
sound=Mix_LoadWAV( "effect.wav" );

2. Play sound effectThe channelThe Mix_Chunk to play

Mix_PlayChannel(-1, sound, 0);

Number of sound repetitions

3. Freeing sound effects

Mix_FreeChunk( her);

21
 Events in SDL

An event:a “signal” sent by a device to your application.

• Press a key on the keyboard
• Mouse click
• Move the mouse
• Minimize/close window

22
 Events in SDL

To read an event you must:

1. declare a variable of type SDL_Event
2. Read the event with one of these functions:

● SDL_Pollevent: reads the event without blocking the game loop

● SDL_waitEvent: remains waiting until listening to an event

Note: if you have automatic processing that does not depend on the user
such as background animation, enemy movement, etc.,
you better use the first function: SDL_PollEvent

23
 Events in SDL

➢ Consider the following code to read an event:

SDL_Event event;

SDL_PollEvent(&event); // to call in the game loop

➢ To detect a keyboard key press, simply compare the event type with:

if(event.type==SDL_KEYDOWN)

➢ To know which key was pressed, you must make this comparison:
if(event.key.keysym.sym == key_name)
Example :if(event.key.keysym.sym ==SDLK_ESCAPE)
24
SDL KEY CODE
 Events in SDL

➢ To detect a mouse movement, simply compare the event type with:

if(event.type==SDL_MOUSEMOTION)

➢ To detect a mouse click, simply compare the event type with:

if(event.type==SDL_MOUSEBUTTONUP) //or SDL_MOUSEBUTTONDOWN
➢ To know where the mouse movement/click took place, you must test if the position of the mouse
mouse is above the desired surface with coordinate (X,Y,W,H):

if(event.motion.x> =X && event.motion.x<=X+W &&

event.motion.y>=Y&& event.motion.y<=Y+H)
26
 Events in SDL
Example: Declare an SDL_Event type variable

Reading events
Returns 1 if there is an event
0 otherwise

27
 Work to do

Implementation of a game menu according to specifications.

Noticed : When compiling code that uses SDL library
functions, you must add the following options in the
linking step:
- lSDL

- lSDL_ttf Example :
- lSDL_image
- lSDL_mixer
 References

● SDL documentation:https://www.libsdl.org , consulted on

01/26/2022