snow.c File Reference

This application shows animated snow in text mode. More...

#include <Uefi.h>
#include <Library/UefiLib.h>
#include <Library/UefiBootServicesTableLib.h>
#include <UEFIStarter/core.h>

Data Structures
struct	flake_t
	data type describing a snowflake More...

Macros
#define	FLAKE_SCREEN_WIDTH   _screen_width
	the snowflake canvas width
#define	FLAKE_SCREEN_HEIGHT   (_screen_height-2)
	the snowflake canvas height
#define	FLAKE_DEFAULT_DURATION_SECONDS   60
	the default time (in seconds) this application should run
#define	FLAKE_DEFAULT_UPDATE_INTERVAL_MILLISECONDS   100
	the default update interval (in ms) between frames
#define	FLAKE_DEFAULT_COUNT   100
	the default number of flakes, including off-screen ones
#define	FLAKE_DEFAULT_GROUND_LIFETIME   10
	the default lifetime (in seconds) of snowflakes on the ground
#define	FLAKE_CROSS_STEP   0.3
	the default wind acceleration step size
#define	FLAKE_MAX_CROSS_SPEED   2.0
	the default maximum wind speed
#define	FLAKE_CROSS_SPEED_FALLOFF_MULT   0.8
	the default wind speed falloff multiplier
#define	FLAKE_CROSS_SPEED_BASE   0.1
	the default base wind speed
#define	ARG_SECONDS   _argument_list[0].value.uint64
	helper macro to access application lifetime parameter
#define	ARG_FLAKE_COUNT   _argument_list[1].value.uint64
	helper macro to access flake count parameter
#define	ARG_UPDATE_INTERVAL   _argument_list[2].value.uint64
	helper macro to access update interval parameter
#define	ARG_GROUND_LIFETIME   _argument_list[3].value.uint64
	helper macro to access ground lifetime parameter
#define	ARG_CROSS_STEP   _argument_list[4].value.dbl
	helper macro to access wind acceleration step size parameter
#define	ARG_MAX_CROSS_SPEED   _argument_list[5].value.dbl
	helper macro to access max wind speed parameter
#define	ARG_CROSS_SPEED_FALLOFF_MULT   _argument_list[6].value.dbl
	helper macro to access wind speed falloff parameter
#define	ARG_CROSS_SPEED_BASE   _argument_list[7].value.dbl
	helper macro to access base wind speed parameter

Functions
UINT32	random ()
	This generates a very-pseudo random number. More...
void	init_flake (flake_t *flake, int time_offset)
	Initializes a snowflake. More...
int	update_flakes (flake_t flakes[], int iteration, float cross_speed, int land_times[])
	Handles snow flake movement for a single frame of animation. More...
EFI_INPUT_KEY	read_key ()
	Reads keyboard input and returns the pressed key. More...
void	print_cross_speed (double speed)
	Debugging function: prints the current wind speed if SHOW_CROSS_SPEED is defined. More...
void	update_ground (int iteration, int land_times[])
	Removes any expired snowflakes on ground. More...
void	do_print_snow ()
	Main animation loop.
void	clear ()
	Clears the screen.
INTN EFIAPI	ShellAppMain (UINTN argc, CHAR16 **argv)
	Main function, gets invoked by UEFI shell. More...

Variables
static cmdline_argument_t	_argument_list []
	command-line arguments More...
static cmdline_argument_group_t	_arguments ={ L"Weather options (in a UEFI boot time executable, mind you)" ,sizeof( _argument_list )/sizeof(cmdline_argument_t), _argument_list }
	command-line argument group
static UINTN	_screen_width
	internal storage for screen's total width (in characters)
static UINTN	_screen_height
	internal storage for screen's total height (in characters)
static UINTN	_ground_lifetime_frames
	internal storage for snowflake's ground lifetime (in number of frames)

Detailed Description

This application shows animated snow in text mode.

Press the reft/right arrow keys for wind. Press 'q' to quit.

Author

Richard Nusser

Copyright

2017-2018 Richard Nusser

License

GPLv3 (see http://www.gnu.org/licenses/)

See also

https://github.com/rinusser/UEFIStarter

Function Documentation

random()

UINT32 random

(

)

This generates a very-pseudo random number.

Don't use this function for anything but trivial applications, the numbers are nowhere near random.

Returns

a number random enough for this application

Todo:

There's a GetRandomNumber32() function in EDK2 but it seems to segfault all the time, see what's up

init_flake()

void init_flake	(	flake_t *	flake,
		int	time_offset
	)

Initializes a snowflake.

Parameters

flake	the flake to initialize/reset
time_offset	the time of the flake's creation

Todo:

use screen height and max cross speed to accurately calculate this

update_flakes()

int update_flakes	(	flake_t	flakes[],
		int	iteration,
		float	cross_speed,
		int	land_times[]
	)

Handles snow flake movement for a single frame of animation.

This function doesn't handle flakes on the ground: those are actually just visual artifacts. The snowflakes fall "through" the ground, get reset to above the screen and start from there. The flakes seen on the ground were just never removed during animation. Instead the flake's landing time is written to land_times, update_ground() will draw over those flakes that landed more than the configured ground lifetime ago.

Parameters

flakes	the snowflakes' data
iteration	the animation loop iteration number
cross_speed	the current wind speed
land_times	the list of flakes' last landing times, one entry per text column

Returns

the number of currently moving snowflakes; on error the (1-based) snowflake number the error happened at

read_key()

EFI_INPUT_KEY read_key

(

)

Reads keyboard input and returns the pressed key.

Some terminals and terminal multiplexers generate multiple input events for just one keystroke (e.g. escape sequences), this will return the last of them.

Returns

the pressed key

print_cross_speed()

void print_cross_speed

(

double

speed

)

Debugging function: prints the current wind speed if SHOW_CROSS_SPEED is defined.

Parameters

speed

the wind speed to print

update_ground()

void update_ground	(	int	iteration,
		int	land_times[]
	)

Removes any expired snowflakes on ground.

Parameters

iteration	the current animation iteration number
land_times	the last flake landing times per text column

ShellAppMain()

INTN EFIAPI ShellAppMain	(	UINTN	argc,
		CHAR16 **	argv
	)

Main function, gets invoked by UEFI shell.

Parameters

argc	the number of command-line arguments passed
argv	the command-line arguments passed

Returns

an EFI status code for the shell

Variable Documentation

_argument_list

cmdline_argument_t _argument_list[]

static

Initial value:

= {
  {{uint64:FLAKE_DEFAULT_DURATION_SECONDS},            ARG_INT,   NULL,L"-duration",           L"Duration (in seconds) snow should fall"},
  {{uint64:FLAKE_DEFAULT_COUNT},                       ARG_INT,   NULL,L"-count",              L"Number of flakes generated (about half of them on screen)"},
  {{uint64:FLAKE_DEFAULT_UPDATE_INTERVAL_MILLISECONDS},ARG_INT,   NULL,L"-interval",           L"Interval (in milliseconds) between frames"},
  {{uint64:FLAKE_DEFAULT_GROUND_LIFETIME},             ARG_INT,   NULL,L"-lifetime",           L"Lifetime (in seconds) of flakes on ground"},
  {{dbl:FLAKE_CROSS_STEP},                             ARG_DOUBLE,NULL,L"-cross-step",         L"Crosswind increment step"},
  {{dbl:FLAKE_MAX_CROSS_SPEED},                        ARG_DOUBLE,NULL,L"-max-cross-speed",    L"Maximum crosswind speed"},
  {{dbl:FLAKE_CROSS_SPEED_FALLOFF_MULT},               ARG_DOUBLE,NULL,L"-cross-falloff-multi",L"Crosswind speed falloff multiplier (keep <=1.0)"},
  {{dbl:FLAKE_CROSS_SPEED_BASE},                       ARG_DOUBLE,NULL,L"-base-cross-speed",   L"Base crosswind speed"}
}

command-line arguments