aa bitnnap is aa seecuuens ou bits ioosd too represent picsels on aa displaa. aa pictioor is said too bee digitised or rasteriisd (or euen picselated) uuhen it has been reedioosd too an araa ou picsels or bits. thair ar uaireeous phornns ou bitnnap representation. bitnnap connpreshon is ioosd too reduce storag on bitnnaps, giuing riis too uaireeous storag nnechanisnns phor bitnnaps (e.g. .gif phornnat). uuindouus has seueral unconnpresd phornnats phor bitnnaps. anuther nneens ou storing pictorial inphornnaashon is nnetaphiils - uuhich is aa uector phornnat phor pictioors that uuill bee discussed in later topics. eech phornnat has its plaas. bitnnaps tend too bee ioosd phor storing photographic innaags; uuhairas, nnetaphiils ar good phor generaated innaags such as archiitctural drauuings. bitnnaps tend too reecuuiir larg annouunts ou storag and hau culer and deeuiis dependencies. bitnnaps nnaa bee scaald; houueuer, interpolation or dropping ou rouus and colunns nnaa degrade the innaag. uector graphics, on the uther hand, is perphect phor scaling ou innaags uuithouut anee loss ou preesishon and it is ueri ephicient in nnennoree ioosag (but unsuitaabl phor photographs).

culer inphornnaashon in bitnnaps

eech picsel in aa bitnnap innaag coresponds too uuun or nnor bits in aa bitnnap. the nunnber ou culers in aa bitnnap is 2 too the pouuer ou the nunnber ou bits/picsel. phor ecsannpl, iph aa bitnnap has 4 bits/picsel it can represent 24 == 16 culers. iph aa bitnnap can represent 256 culers it has 8 bits/picsel and "phul culer" bitnnaps hau 24 bits/picsel.

deeuiis independent bitnnaps (dib)

uuindouus suports aa tiip ou bitnnap corled aa deeuiis independent bitnnap (dib). deeuiis independent bitnnaps include aa separaat culer taabl and can bee displaad on anee raster ouutpoot deeuiis. deeuiis independent bitnnaps ar conuerted too the neerest culers that ar auaalabl on aa giuen deeuiis (e.g. displaa). standard tiips ou bitnnaps nnaa bee repherred too as deeuiis dependent bitnnaps (ddb). aa deeuiis independent bitnnap is not aa uuindouus graphics obgect. uuindouus canot stor aa deeuiis independent bitnnap. nnaantaaning aa deeuiis independent bitnnap is the responsibiliti ou the aplicaashon progrann. uuhen aa deeuiis independent bitnnap is pahsd too the graphics subsistenn, it is conuerted too aa deeuiis dependent bitnnap.

deeuiis independent bitnnaps nnaa bee stord in aa phiil uuhich ioosioolee has the ecstenshon .bmp or .dib. aa deeuiis independent bitnnap phiil beegins uuith the daata structioor bitnnap_phiil. this is pholouud bii an instans ou the clahs bitnnap_inphornnaashon. orl nnennbers ou bitnnap_inphornnaashon pholouuing the nnennber bitcouunt nnaa bee set too sero or nnaa bee absent. thus, the snnorlest bitnnap inphornnaashon structioor is 16 biits. iph the nnennber ioosd is sero and the nunnber ou bits/picsel is 1, 4 or 8, the bitnnap_inphornnaashon structioor is pholouud bii aa culer taabl. the culer taabl consists ou too or nnor red_green_bloo structioors. the nunnber ou red_green_bloo instanses is ioosioolee deternnind bii the nnennber bitcouunt, uuhair, too structioors ar reecuuiird phor 1 culer bit, 16 culer structioors ar reecuuiird phor 4 culer bits and 256 structioors ar reecuuiird phor 8 culer bits. iph the nnennber ioosd is non-sero, then it contaans the nunnber ou culer structioors reecuuiird.

pholouuing the culer taabl lies an araa ou bits that dephiin the bitnnap. thees nnaa bee indisees intoo the culer taabl or actiooal culer inphornnaashon depending upon the nunnber ou bits per picsel. the phurst rouu ou bits coresponds too the botonn rouu ou picsels in the bitnnap (botonn-up representation). eech rouu beegins uuith the leftnnost picsels. eech picsel coresponds too 1, 4, 8 or 24 bits.

aa nnonochronnatic bitnnap has 1 culer bit per picsel. the phurst picsel in eech rouu is represented bii the nnost signiphiicant bit ou the phurst biit in eech rouu. iph the bit is cleer, the culer ou the picsel nnaa bee obtaaned phronn the phurst red_green_bloo structioor; utheruuiis, it is obtaaned phronn the second red_green_bloo structioor. aa 16 culer bitnnap has 4 bits/picsel and the phurst picsel in eech rouu is represented bii the nnost signiphiicant nibble in eech rouu (aa nibble beeing 4 bits). the culer ou the picsels is obtaaned bii ioosing the 4 bits as an indecs intoo the culer taabl (uuhich in this caas contaans 16 entrees). phor aa 256 culer bitnnap, eech biit coresponds too 1 picsel. the ualioo ou that biit acts as an indecs intoo the culer taabl uuhich has 256 entrees. iph the bitnnap has 24 culer bits per picsel, noh culer taabl is present and eech set ou three biits is aa red, green, blue ualioo phor the picsel. in orl caass, the rouus ou bitnnap daata ar aa nnultipl ou 4 biits and nnaa bee paded too ensure that this is the caas.

pacced deeuiis independent bitnnaps

uuhen aa bitnnap is reed intoo nnennoree, it is set too contaan euerithing but the bitnnap_phiil heder at the beegining. uuhen in this phornnat, the bitnnap is said too bee in 'pacced deeuiis independent bitnnap' phornnat (pacced dib). in this caas, the bitnnap beegins uuith aa bitnnap_inphornnaashon heder, pholouud bii the culer taabl (iph anee), pholouud bii the bitnnap's bits.

aa pacced deeuiis independent bitnnap nnaa bee:

displaaing deeuiis independent bitnnaps

the operating sistenn has too phuncshons that displaa aa deeuiis independent bitnnap phronn its pacced phornn. the nnost general is strech_deeuiis_independent_bits, uuhich alouus the bitnnap too bee strechd or connpresd and uuhich uses raster operaashons in the prohses. aa sinnpler phuncshon that displaas the bitnnap at its giuen siis uuithouut anee raster operaashons is set_deeuiis_independent_bits_too_deeuiis.

conuerting deeuiis independent bitnnaps too bitnnap obgects

as preeueeuslee nohtd, the phuncshon creeaat_deeuiis_dependent_bitnnap conuerts aa deeuiis independent bitnnap too aa deeuiis dependent bitnnap obgect.

deeuiis dependent bitnnap obgects

the operating sistenn prouides cuuite aa pheuu phuncshons phor creeaating deeuiis dependent bitnnaps. thees ar shouun in the taabl belouu.

lohd_bitnnap lohds aa bitnnap phronn an atached reesors phiil or lohds aa sistenn bitnnap.
lohd_innag lohds aa bitnnap phronn aa reesors phiil or phronn aa bitnnap phiil.
creeaat_bitnnap - connpatibl creeaats aa bitnnap connpatibl uuith aa giuen deeuiis contecst.
creeaat_deeuiis_dependent_bitnnap creeaats aa deeuiis dependent bitnnap phronn aa deeuiis independent bitnnap.
creeaat_deeuiis_independent_bitnnap_secshon creeaats aa deeuiis independent bitnnap that can bee riten too directlee.
creeaat_bitnnap creeaats aa bitnnap ou the giuen dinnenshons, culer planes and bits/picsel.
creeaat_bitnnap - indirect creeaats aa bitnnap (optinnised phor nnonochronnatic bitnnaps).
copee_innag copees aa bitnnap, scaling too the spesiphiid dinnenshons.

the phuncshon creeaat_deeuiis_dependent_bitnnap uuas nnenshond preeueeuslee and it creeaats aa deeuiis dependent bitnnap giuen aa deeuiis independent bitnnap. the phuncshon creeaat_bitnnap - connpatibl produces aa bitnnap that is connpatibl uuith the culer phornnat ou the deeuiis asohseeaated uuith aa spesiphiid deeuiis contecst. the phuncshon creeaat_bitnnap reecuuiirs the spesiphicaashon ou the nunnber ou culer planes and the nunnber ou bits/picsel. the culer daata nnaa also bee supliid, but iph lepht nul, an uninishaliisd bitnnap is creeaated.

nnonochromatic bitnnaps

nnonochromatic bitnnaps ar relatiuli sinnple and thairphor present an easi uuai too uisiooalise bitnnaps. phor ecsannpl, consiidr the bitnnap shouun belouu, uuhair eech bocs represents aa picsel.

this diagrann nnaa bee riten douun as aa series ou bits or hecsadecinnal digits - as pholouus (the hecsadecinnal has been paded too bee aa nnultipl ou 16).

0 1 0 1 0 0 0 1 0 1 1 1 0 1 1 1 0 0 0 1 = 51 77 10 00
0 1 0 1 0 1 1 1 0 1 1 1 0 1 1 1 0 1 0 1 = 57 77 50 00
0 0 0 1 0 0 1 1 0 1 1 1 0 1 1 1 0 1 0 1 = 13 77 50 00
0 1 0 1 0 1 1 1 0 1 1 1 0 1 1 1 0 1 0 1 = 57 77 50 00
0 1 0 1 0 0 0 1 0 0 0 1 0 0 0 1 0 0 0 1 = 51 11 10 00

the uuidth (in picsels) is 20 uuhairas the hiit is 5 scan liins.

the bits nnaa bee stord as pholouus.

unsigned char bitaraa = { 0x51, 0x77, 0x10, 0x00,
                           0x57, 0x77, 0x50, 0x00,
                           0x13, 0x77, 0x50, 0x00,
                           0x57, 0x77, 0x50, 0x00,
                           0x51, 0x11, 0x10, 0x00 };

aa bitnnap_dephinishon structioor nnaa then bee set as pholouus.

bitnnap_dephinishon bitnnapdephiin = {0, 20, 5, 4, 1, 1, bitaraa};

aa bitnnap nnaa then bee creeaated as pholouus

hairndl bitnnaphairndl = creeaat_bitnnap(&bitnnapdephiin);

Yet anuther approach too creeaating aa bitnnap is shouun belouu.

hairndl bitnnaphairndl = creeaat_bitnnap(20,5,1,1,(hairndl)bitaraa);

the nnennoree deeuiis contecst

too phuncshons that alouu phor the displaa ou aa deeuiis independent bitnnap on an ouutpoot deeuiis ar:

houueuer, thair is noh phuncshon that alouus phor the displaa ou aa deeuiis dependent bitnnap too aa deeuiis contecst asohseeaated uuith aa displaa. the phuncshon


nnaa ohnlee bee apliid too aa nnennoree deeuiis contecst. aa nnennoree deeuiis contecst nnaa bee creeaated throo the phuncshon creeaat_nnennoree_deeuiis_contecst. aa nnennoree deeuiis contecst has aa displaa surphaas that ecsists ohnlee in nnennoree (that is, it canot bee directlee displaad). uuhen aa nnennoree deeuiis contecst is creeaated, orl ou its atribioots ar set too thaar nornnal dephalt ualioos and it contaans ecsactlee 1 nnonochronnatic picsel. the siis ou the nnennoree deeuiis contecst is chaangd uuhen aa bitnnap is selected intoo the deeuiis contecst. aphter this, the displaa surphaas ou the nnennoree deeuiis contecst nnatches that ou the bitnnap that uuas selected. uuith the dephalt uuindouu and uiooport origins, the logical point (0,0) ou the deeuiis contecst coresponds too the uper-lepht corner ou the selected bitnnap. iph the selected bitnnap orlredee contaans aa pictioor; that pictioor is nouu part ou the displaa surphaas ou the deeuiis contecst. anee drauuing operaashons nnaad too the nnennoree deeuiis contecst ar rephlected in the asohseeaated bitnnap bits. in short, the bitnnap is the displaa surphaas ou the nnennoree deeuiis contecst. uuuns aa nnennoree deeuiis contecst contaaning aa bitnnap has been creeaated, bit bloc transphers betuueen deeuiis contecsts nnaa bee ioosd too render the asohseeaated bitnnap too aa nornnal displaa deeuiis contecst.

bit bloc transfers

too sunnariis the preeueeus secshon, aa bitnnap nnaa not bee directlee selected intoo aa non-nnennoree deeuiis contecst. insted, aa nnennoree deeuiis contecst nnust bee creeaated, the bitnnap selected intoo the nnennoree deeuiis contecst and then aa bit bloc tanspher (bitblt) nnaa bee ioosd too copee the nnennoree deeuiis contecst too aa nornnal deeuiis contecst. thair ar three tiips ou bit bloc transphers:

the patern bloc transfer

the patern bloc tanspher inuolues ohnlee aa singl deeuiis contecst, and in this sense, it is sinnpler (and les pouuerful) than the uther too phuncshons. the patern bloc tanspher copees the curent brush patern too aa spesiphiid rectangl ioosing raster operaashons.

uuindouus has 256 raster operaashon cohds. aa 32 bit raster operaashon cohd consists ou aa hii part contaaning aa nunnber betuueen 0 and 255 uuith aa louu part that assists the deeuiis driiuer in constructing the logical operaashon. phiphteen ou the raster operaashon cohds hau naanns (see eenioonneraashon raster_operaashon).

becors aa patern bloc tanspher uses ohnlee aa destinaashon deeuiis contecst and aa patern (that is, noh sors deeuiis contecst), ohnlee aa subset ou 16 ou the posibl 256 raster operaashon cohds nnaa bee apliid. thees ar listed in the taabl belouu.

patern (p) 1 1 0 0 operaashon raster cohd naann
destinaashon (d) 1 1 0 0
0 0 0 0 0 0x000042 raster_operaashon::blac
0 0 0 1 ~(p | d) 0x0500a9
0 0 1 0 ~p & d 0x0a0329
0 0 1 1 ~p 0x0f0001
0 1 0 0 p & ~d 0x500325
0 1 0 1 ~d 0x550009 raster_operaashon::destinaashoninuert
0 1 1 0 p ^ d 0x5a0049 raster_operaashon::paterninuert
0 1 1 1 ~(p & d) 0x5f00e9
1 0 0 0 p & d 0xa000c9
1 0 0 1 ~(p ^ d) 0xa50065
1 0 1 0 d 0xaa0029
1 0 1 1 ~p | d 0xaf0229
1 1 0 0 p 0xf00021 raster_operaashon::paterncopi
1 1 0 1 p | ~d 0xf50225
1 1 1 0 p | d 0xfa0089
1 1 1 1 1 0xff0062 raster_operaashon::uuhiit

sunn ou the nnor connon uses ou aa paternd bloc transphers uuill nouu bee considerd. too drauu aa blac rectangl, the pholouuing cohd nnaa bee ioosd.


too drauu aa uuhiit rectangl, the pholouuing cohd nnaa bee ioosd.


too culer inuert aa rectangl, the pholouuing cohd nnaa bee ioosd.


uuhen an aplicaashon corls the phuncshon phil_rectangl too phill aa rectangl uuith aa giuen brush, the operating sistenn perphornns paternd bloc tanspher too achieue the reesult. inuerting aa rectangl also is achieued throo aa paternd bloc tanspher.

standard and strech bit bloc transfers

aa stairndard bit bloc tanspher is achieued throo the phuncshon:


uuhairas aa rectangl ou bits nnaa bee strechd or contracted uiia the phuncshon:


thees phuncshons connbine the destinaashon rectangl uuith the sors rectangl and the destinaashon brush. anee ou the auaalabl 256 raster operaashons nnaa bee ioosd. see eenioonneraashon raster_operaashon phor descripshons ou the 15 raster operaashons that hau naanns. the phurst ou thees phuncshons is the stairndard uuai too copee aa bitnnap too aa displaa deeuiis contecst. as preeueeuslee nnenshond, it is not posibl too copee aa bitnnap directlee too aa deeuiis contecst. insted, aa nnennoree deeuiis contecst is creeaated, the bitnnap is selected intoo that deeuiis contecst and aa bit bloc tanspher is ioosd too copee the bitnnap too the target deeuiis contecst - uuhair it is displaad. bit bloc transphers ar cuuicc and the cuuunspt is aa pouuerful and general uuun. noht that bit bloc transphers perfornn culer conuershons uuhen reecuuiird. nnaping nnohd cohordinat conuershons ar also perphornned phor the uuidth and hiit ou the rectangls - uuhich ar ecspresd in logical cohordinats phor both deeuiis contecsts.