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>> [Music kucheza]

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>> ZAMYLA CHAN: Hebu pigo
mambo ya juu na resize.

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Katika resize, user itapita katika, kupitia
mstari amri, bitmap picha kwamba

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wanataka kuongeza kwa idadi
kwamba wao pia kupita katika,

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katika mstari amri.

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Jinsi gani tunafanya hivi?

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>> Naam, mambo ya kwanza ya kwanza, hebu
kuvunja chini katika hatua.

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Wewe ni kwenda unataka kufungua infile
kwamba wao kukupa, kama vile

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kujenga na kufungua outfile kwamba
wewe ni kwenda kuweka

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resized picha in

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Basi, kwa sababu wewe ni resizing, na
kwa sababu ni bitmap, ni header, hivyo

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utaenda pia update header
habari kwa ajili ya outfile,

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na kuandika kwamba in

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Basi, wewe ni kwenda kusoma katika
scanline ya infile,

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pixel-na-pixel, resizing usawa
na kuandika saizi wale katika

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outfile, kama maalum
na mtumiaji wadogo.

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>> Wewe ni kwenda kukumbuka
kuongeza padding kama ni muhimu.

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Zaidi juu ya baadaye.

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Na kisha, pia resize wima.

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OK.

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Hivyo hii ni kwenda kuwa kidogo zaidi
ngumu zaidi ya nani kufanya jambo hilo, lakini

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nini sawa ni kwamba copy.c mapenzi,
tena, kuthibitisha muhimu sana.

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Kumbuka kwamba copy.c kufungua faili,
updates header habari kwa ajili ya

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outfile, basi wasomaji katika scanline,
pixel-na-pixel, kuandika kila pixel

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katika pato faili scanline.

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>> Hivyo tena, hatua yako ya kwanza nguvu pengine
kuwa na linganisha, copy.c, resize.c

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ndani ya PSET5 saraka yako.

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Kumbuka ingawa, kabla ya nakala yake,
kuhakikisha kwamba kuelewa

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copy.c vyema.

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OK.

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>> Basi hebu kufungua faili.

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Unajua jinsi ya kufanya hivyo.

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Mimi naenda kuondoka hivyo na wewe.

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Next, update header habari
kwa outfile.

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Kwa sababu tuna bitmap mpya,
tuna mpya header info.

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Nini kubadilisha hapa?

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Naam, faili ni kwenda na mabadiliko
kwa sababu tunakwenda na zaidi

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saizi kuliko hapo kabla.

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ukubwa picha, hivyo, pia
kwenda na mabadiliko, kama ni

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upana na urefu.

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>> Hivyo ambayo vigezo ni wale, hasa?

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Naam, kama ukiangalia katika header
habari, unaweza kuona kuna

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biSizeImage, ambayo inawakilisha jumla
ukubwa wa picha katika ka,

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ikiwa ni pamoja na saizi na padding.

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biWidth ni upana wa picha
katika saizi, minus padding.

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biHeight ni urefu wa
picha katika saizi.

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Na hivyo wale zilizomo katika
structs BITMAPFILEHEADER na

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BITMAPINFOHEADER.

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Unaweza kuwaambia ambayo ni moja ambayo na
kwenda bmp.h na kuangalia

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BITMAPINFOHEADER struct na kuona
ambayo vigezo ni waliotajwa huko.

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>> Hivyo update header outfiles
habari, wewe ni atataka

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kubadili maadili wale wa
urefu na upana.

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Lakini nafasi ni, unaweza haja ya baadhi ya
ya infile ya header habari

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baadaye, hivyo bora kwa kuweka wimbo wa wote.

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Lakini kuwa wazi sana na kutofautiana yako
majina ili kufanya si ajali

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kuandika maadili sahihi katika
header kwa outfile.

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>> Hivyo sasa hebu kupata kusoma katika
scanline pixel-na-pixel.

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Tena, tunakwenda kurejea kwa muaminifu wetu
faili I / O maktaba, na kuangalia

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kazi fread.

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fread inachukua katika pointer kwa struct
ambayo yana ka kwamba

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wewe ni kusoma katika, ukubwa wa kila
hiki kwamba wewe ni kusoma -

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tena, sizeof ni kwenda kuwa na manufaa
kazi hapa, idadi ya

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mambo ya kawaida, ukubwa, kwamba wewe ni
kusoma, na kisha hatimaye,

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inpointer, faili kwamba
wewe ni kusoma kutoka.

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Hivyo wewe ni kuchukua vipengele namba
ya kawaida kutoka inpointer, na

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kuweka katika data.

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>> Sasa ni wakati wa resize usawa.

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kama n sawa na 2, kisha kwa kila pixel katika
infile, tunakwenda kuandika

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mara mbili katika outfile.

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Je, sisi kuandika files?

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Naam, tuna kazi fwrite, hivyo
tumekuwa kuchukuliwa pointer kwa struct

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ambayo ina ka kwamba wewe ni
kuandika kutoka, na kisha sisi kupita katika

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kawaida, idadi, na pato, ambapo
wewe ni kwenda kuwa kuandika hiyo.

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Na kisha kurudia utaratibu, itakuwa
uwezo iterative rahisi kwa kitanzi.

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>> Lakini tunahitaji kukumbuka
kuongeza padding in

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dhana ya padding ni kwamba, vizuri,
kila pixel ni kuumwa tatu, lakini

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ukubwa wa kila lazima scanline
kuwa nyingi ya 4 ka.

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Hivyo kama idadi ya saizi ni si
mbalimbali ya 4, tunahitaji kuongeza baadhi

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padding, ambayo ni zeroes tu.

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Sasa, tofauti na nani kufanya jambo hilo, na tofauti na
nakala, kisha infile picha na

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outfile file kuwa tofauti na
padding mbalimbali kwa sababu wao ni

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widths mbalimbali.

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>> OK.

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Hivyo labda formula ingekuwa
kuja katika Handy hapa.

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Mimi itabidi kuondoka kwa wewe kupata nje, lakini
kuwaambia kwamba, kuandika padding,

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vizuri, ni rahisi tu fputc kazi,
kupita katika tabia ya

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kwamba unataka kuandika, na kisha
file pointer kwamba

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unataka kuandika kwa.

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Hivyo sasa kwamba tumekuwa resized usawa,
na kisha kutumika padding,

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kukumbuka kwamba unahitaji hoja faili yako
nafasi kiashiria, kwa sababu wewe

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hawezi fread katika padding.

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Kwa hiyo unataka kuhakikisha kwamba faili yako
nafasi kiashiria katika infile

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ni katika hatua sahihi.

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Kwa sababu sisi pia wanataka
resize wima.

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Hatuwezi tu kunyoosha usawa,
kwa sababu mahitaji ya kila mstari

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kunakiliwa mara n.

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>> Sasa, kuna mbalimbali
njia za kufanya hivyo.

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Hivyo moja, tunaweza kutumia njia rewrite, katika
kwamba sisi kukumbuka yote ya saizi

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ya kupewa mfululizo katika safu, na
kisha sisi kuandika kwamba safu kama

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mara nyingi kama inahitajika.

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Au kuna njia recopy ambapo,
baada ya kusoma katika mstari mmoja katika infile

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na kisha kuandika kwamba ndani ya outfile,
kuongeza padding, sisi fseek

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nyuma ya kuanza kwa mstari awali,
na kisha kurudia usawa

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resizing kutoka huko.

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Bila kujali njia, ingawa, wewe utakuwa
nataka kila pixel kuwa mara kwa mara

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n mara kwa mara, na kila mstari kuwa
mara kwa mara mara n pia.

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>> Pamoja na kwamba, itabidi bitmap
kubwa kuliko maisha.

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Jina langu ni Zamyla, na hii ni CS50.

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