Using random numbers Some ways the standard UNIX rand library function can be deployed to generate graphics and sound Automating pattern creation Use these standard runtime functions include stdlib h int rand void void srand unsigned int seed Make a new 8x8 bitmap pattern like this unsigned char pat 8 for k 0 k 8 k pat k rand fgcolor rand bgcolor rand Esthetics Use a brighter color in the foreground Use a darker color in the background To implement this discipline we need to know how the color table is arranged In mode 19 there are 256 default colors Among these are 24 color groups 3 intensity levels plus 3 saturation levels The default colors mode 19 Range for the 72 brightest colors 32 103 Range for the 72 midlevel colors 104 175 Range for the 72 darkest colors 176 247 Colors 0 15 are the standard EGA colors Colors 16 31 are sixteen grayscale colors Colors 248 255 are solid black default But all of these are fully programmable Choosing a random color pair foreground color from the bright range fgcolor rand 0xFF 72 32 Background color from the dark range bgcolor rand 0xFF 72 104 Using patterns with more colors Same concepts can be extended But need a larger pattern bitmap Example use 2 bits per pixel 4 colors An 8x8 pattern that using 4 colors unsigned short pat2bpp 8 unsigned char palette4 4 for r 0 r 8 r pat2bpp r rand for c 0 c 4 c palette4 c rand Tiling with a 4 color bitmap for y 0 y hres y unsigned short bits pat2bpp y 8 for x 0 x hres x int i bits x 8 3 int color palette4 i vram y hres x color Automating an art show Can use a standard C runtime function include unistd h void sleep int seconds User views your screen for fixed duration while done draw next scene sleep 1 In class exercise 1 Can you use the UNIX random number generator function to create an art show i e a succession of esthetically pleasing patterns that tile the display screen for a timed duration Generating white noise We can use the rand function to create pulse code data for a Waveform Audio file When we play that wav file what we will hear is a sound known as white noise Let s look at the details for IBM Microsoft Waveform Audio file format wav their original simple version Version 1 0 It s contents is organized into chunks The Waveform Audio File Format RIFF Chunk 12 bytes FORMAT Chunk 24 bytes DATA Chunk size varies Version 1 0 Developed jointly in 1991 by IBM and Microsoft Corporation for the Windows 3 1 operating system The RIFF chunk RIFF Resource Interchange File Format 12 bytes RIFF Total number of the file s bytes that follow WAVE chunkName ascii characters chunkSize unsigned int chunkType ascii characters Remainder of the RIFF chunk holds all the file s other chunks The FORMAT chunk fmt ascii characters formatTag i e 0 or 1 nChannels mono 1 or stereo 2 avBytesPerSec Number of chunk s bytes that follow i e 16 samplesPerSec e g 44100 frameAlignmt bitsPerSample i e 1 2 4 e g 8 or 16 Originally was a fixed size header 8 bytes plus parameters 16 bytes TOTAL SIZE 24 bytes The DATA chunk data ascii characters Number of chunk s bytes that follow i e 16 The PCM data goes here Pulse Code Modulation size is variable 8 Bit Sample Formats 8 bit monoaural Each sample is one byte Value is an unsigned char in range 0 255 The neutral value is 128 i e silence 8 bit stereo Each sample is a byte pair First sample value is for left hand channel second sample value is right hand channel 16 Bit Sample Formats 16 bit monoaural sample size is two bytes Value is a short in range 32768 32767 The default storage convention is Big Endian The neutral value is 0 i e silence 16 bit stereo sample size is four bytes First sample value is for left hand channel second sample value is right hand channel Our mknoises cpp demo Program creates a file named noises wav It demonstrates stereophonic white noise First the left hand channel plays white noise Then right hand channel plays white noise Uses 8 bit stereo sample format Left channel pulse code Right channel pulse code Each sample stores a pair of 8 bit pulse code values In class exercise 2 Can you modify the mknoises cpp demo so that noise from the left hand channel gradually diminishes in volume while the noise from the right channel is gradually getting louder
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