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* \file
* This example program creates a window and displays a sprite in the middle
* of it. The user can move the sprite using the stick of the first joystick's.
* Two buttons are used to rotate the sprite clockwise and anticlockwise. Two
* other buttons flip the sprite horizontally and vertically. Again, two other
* buttons are used to increase and decrease the size of the sprite.
* In order to make this example minimalistic, it will not use most of the
* functionalities of the Bear Engine. Consequently, we will have manage the
* exit of the program ourselves.
* The SDL is used for the subsystems of the engine. Thus we can use its event
* system to detect when the user wants to quit the program.
#include "visual/screen.hpp"
#include "visual/scene_sprite.hpp"
#include "time/time.hpp"
#include "input/system.hpp"
#include "input/joystick.hpp"
#include "SDL2/SDL.h"
#include <fstream>
* This global variable is observed in the main loop in order to exit the
* program as it becomes true.
bool g_quit(false);
* This function processes an event of the SDL. If the quit signal has been
* sent, then g_quit is set to true. Otherwise the function does nothing.
* \param user_data Ignored.
* \param event The event to process.
int event_filter( void* user_data, SDL_Event* event )
int result(0);
switch ( event->type )
case SDL_QUIT:
g_quit = true;
result = 1;
return result;
* Initializes the visual and input modules of the engine and registers the
* event filter to the SDL.
void init()
bear::visual::screen::initialize( bear::visual::screen::screen_gl );
SDL_SetEventFilter( &event_filter, NULL );
* Releases the visual and input modules of the engine.
void release()
* Creates a sprite given an image file name and a region in this image.
* \param file_name The path to the image used for the sprite.
* \param clip The part of the image to use for the sprite, relatively to the
* top-left corner of the texture.
bear::visual::sprite load_sprite
( const std::string& file_name,
const bear::visual::sprite::clip_rectangle_type& clip )
// Open the image file.
std::ifstream f( file_name.c_str() );
if ( !f )
std::cerr << "Cannot open file \"" << file_name
<< "\" from current directory.\n";
// the engine uses the graphic module of libclaw to load the images. This
// constructor builds a 32 bits color image from files such as PNG, JPEG, TGA,
// Bitmap.
claw::graphic::image image( f );
// Then we create a texture from the loaded image.
bear::visual::image texture( image );
// And we build a sprite from this texture.
return bear::visual::sprite
( /* The texture of which the sprite is part of. */
/* The part of the image to use for the sprite. */
clip );
* Reads the state of the joystick's buttons and applies the corresponding
* transformations to a sprite. The axis moves the sprite, two buttons changes
* the angle, two buttons change the scale and two buttons flip the sprite
* horizontally and vertically.
* \param sprite The sprite to transform.
* \param center The position of the center of the sprite.
void transform_sprite_with_joystick
( bear::visual::sprite& sprite, bear::visual::position_type& center )
// The state of the joystick is supposed to be up to date.
const bear::input::joystick& joystick
( bear::input::system::get_instance().get_joystick(0) );
// The scale that will be applied to the sprite. By default the scale doesn't
// change.
double scale( 1 );
// The length of the movement to be applied on each pressed axis.
const double movement_length(5);
// The angle of the rotation.
const double rotation_delta(0.1);
// bear::input::joystick has both the begin() and end() functions required to
// use range-based loops. The value type of the returned iterator is a code
// identifying a pressed button.
for ( bear::input::joystick::joy_code k : joystick )
switch (k)
case bear::input::joystick::jc_axis_left:
center.x -= movement_length;
case bear::input::joystick::jc_axis_right:
center.x += movement_length;
case bear::input::joystick::jc_axis_down:
center.y -= movement_length;
case bear::input::joystick::jc_axis_up:
center.y += movement_length;
case bear::input::joystick::jc_axis_up_right:
center +=
bear::visual::position_type( movement_length, movement_length );
case bear::input::joystick::jc_axis_down_right:
center +=
bear::visual::position_type( movement_length, -movement_length );
case bear::input::joystick::jc_axis_down_left:
center +=
bear::visual::position_type( -movement_length, -movement_length );
case bear::input::joystick::jc_axis_up_left:
center +=
bear::visual::position_type( -movement_length, movement_length );
case bear::input::joystick::jc_button_1:
sprite.set_angle( sprite.get_angle() + rotation_delta );
case bear::input::joystick::jc_button_2:
sprite.set_angle( sprite.get_angle() - rotation_delta );
case bear::input::joystick::jc_button_3:
sprite.mirror( !sprite.is_mirrored() );
case bear::input::joystick::jc_button_4:
sprite.flip( !sprite.is_flipped() );
case bear::input::joystick::jc_button_5:
scale = 1.2;
case bear::input::joystick::jc_button_6:
scale = 0.8;
bear::visual::size_box_type s( sprite.get_size() * scale );
if ( (s.x > 10) && (s.y > 10) )
sprite.set_size( s );
* \brief Creates a window with a sprite in it, then polls the joystick and
* transforms the sprite according to the inputs.
void run_example()
// Here we create the window; it will be immediately visible.
// The engine does not support multiples windows yet, so be careful and be
// sure to create only one of them.
// As soon as the screen is created, a render thread is created
bear::visual::screen s( claw::math::coordinate_2d<unsigned int>(640, 480) );
bear::visual::sprite sprite
( load_sprite
( /* The path to the image of which the sprite is a part. */
/* The part of the image to use for the sprite, relatively to the
top-left corner of the texture. Values are: left, top, width,
height. */
bear::visual::sprite::clip_rectangle_type(0, 0, 57, 65) ) );
// The position of the center of the sprite in the screen.
bear::visual::position_type sprite_center( s.get_size() / 2 );
while ( !g_quit )
// update the state of the input devices.
// compute the new center of the sprite.
transform_sprite_with_joystick( sprite, sprite_center );
// and build the scene element such that the sprite is centered on
// sprite_center.
bear::visual::scene_sprite element
( sprite_center.x - sprite.width() / 2,
sprite_center.y - sprite.height() / 2, sprite );
s.render( element );
// wait 15 milliseconds before the next update. It is necessary to avoid
// the sprite to move too fast, in this example.
bear::systime::sleep( 15 );
* Initializes the Bear Engine's modules then run the example. The modules are
* released before leaving.
int main( int argc, char* argv[] )
if ( bear::input::joystick::number_of_joysticks() == 0 )
std::cout << "No joystick found. Leaving.\n";
return 1;
return 0;