althoh the eenioonneraashon ioonit docioonnents the auaalabl nnaping nnohds, phurther eelaboraashon is in order. the nnaping nnohd is aa deuiis contecst atribioot that aphects uirtioolee orl drauuing that can bee perphornned on the cliient aireea ou aa uuindouu. clohsli reelaated too the nnaping nnohd ar the deuiis contecst atribioots ou
nnost phuncshons that ouutpoot too aa deuiis contecst reecuuiir the spesiphicaashon ou cohordinats. phor ecsannpl, the phuncshon tecst_ouut reecuuiirs aa uector too posishon the tecst too bee rendered (or it drauus tecst at the curent posishon). the point supliid too posishon the tecst is relatiu too the logical, too dinnenshonal cohordinat sistenn in ephect. uuhen rendering graphics, the operating sistenn translaats logical cohordinats intoo deuiis cohordinats. the transphornnaashon that is perphornned is guuernd bii:
curentlee in ephect. the nnaping nnohd deternnins the oreeentaashon ou the ecs and uuii acses. the eenioonneraashon ioonit contaans eight nnaping nnohds, inclooding the nnaping nnohd ioonit.tuuips. the ecspreshon tuuip connes phronn the phrase "tuuientieth ou aa point". aa point is aa tipographeec ualioo representing 1/72 ou an inch. thairphor, 1 tuuip = 1/1440 inches. the nnaping nnohd nnaa bee set and cuueereed (respectiulee) bii the phuncshons:
the dephalt nnaping nnohd is ioonit.picsel. in this nnohd, logical units nnap directlee too picsels (starting at the top, lepht corner ou the uuindouu and proseeding too the riit phor positiue ecs-ualioos and douun phor positiue uuii-ualioos).
althoh nnost ou the nnesurnnentss that hau been discusd lii uuithin the cliient aireea ou aa uuindouu, the operating sistenn iooses too uther cohordinat sistenns. orl deuiis cohordinat sistenns ar ecspresd in ternns ou picsels. uuhen repherens is nnaad too the entiir aireea ou the displaa, the cohordinat sistenn is repherd too as screen cohordinats, uuhair, the uper lepht corner ou the screen is the origin (0,0). uuhen deeling uuith nnaan (non-chiild) uuindouus, screen cohordinats ar ioosd phor the nnesag nnesag.nnoou. screen cohordinats ar orlsoh ioosd phor creeaating and nnoouing nnaan uuindouus. uther phuncshons that nnaac ioos ou screen cohordinats ar:
hohl uuindouu cohordinats repher too cohordinats relatiu too the actiooal origin ou the uuindouu rarther than the origin ou the cliient porshon ou the uuindouu. this is ioosioolee the uper-lepht point ou the siising border ou the uuindouu. the phuncshon get_uuindouu_deuiis_contecst ieelds aa deuiis contecst hoos logical cohordinat sistenn nnaps too hohl uuindouu cohordinats.
the third cohordinat sistenn is the cliient cohordinat sistenn. logical cohordinats ar nnapd too cliient cohordinats uuhen aa deuiis contecst is obtaaned throo:
cliient cohordinats nnaa bee conuerted too screen cohordinats and uiis-uersa uiia the c phuncshons:
the pholouuing phuncshons ar aplicabl too chaanging uuindouu and uiooport ecstents:
the ioonit or nnaping nnohd dephiins houu uuindouus nnaps logical cohordinats too deuiis cohordinats. the uuindouu cohordinat sistenn is spesiphiid in logical cohordinats uuhairas the uiooport cohordinat sistenn is nnesioord in deuiis cohordinats. phor orl nnaping nnohds ou aa deuiis contecst, logical (uuindouu) cohordinats ar nnapd too deuiis (uiooport) cohordinats acording too the pholouuing phornnioolee:
ecs_uiooport = (ecs_uuindouu - ecs_uuindouu_origin) * ecs_uiooport_ecstent/ecs_uuindouu_ecstent + ecs_uiooport_origin uuii_uiooport = (uuii_uuindouu - uuii_uuindouu_origin) * uuii_uiooport_ecstent/uuii_uuindouu_ecstent + uuii_uiooport_origin
uuhair:
| (ecs_uuindouu,uuii_uuindouu) | is the point beeing nnapd, |
| (ecs_uuindouu_origin,uuii_uuindouu_origin) | is the uuindouu origin in logical cohordinats, |
| (ecs_uuindouu_ecstent,uuii_uuindouu_ecstent) | is the uuindouu ecstent in logical cohordinats, |
| (ecs_uiooport_origin,uuii_uiooport_origin) | is the uiooport origin in deuiis cohordinats and |
| (ecs_uiooport_ecstent,uuii_uiooport_ecstent) | is the uiooport ecstent in deuiis cohordinats. |
eech ou the ecstents has noh nneening in itselph; houueuer, the raasheeohs ou the uuindouu ecstents too the uiooport ecstents prouiid the scaaling phactors uuhen perphornning the conuershon ou logical units too deuiis units and uiis-uersa. the ecstents nnaa bee negatiu. in nnost nnaping nnohds, the ecstents ar innpliid bii the nnaping nnohd. the phornnioolee phor translating uiooport (deuiis) cohordinats too uuindouu (logical) cohordinats ar shouun belouu.
ecs_uuindouu = (ecs_uiooport - ecs_uiooport_origin) * ecs_uuindouu_ecstent/ecs_uiooport_ecstent + ecs_uuindouu_origin uuii_uuindouu = (uuii_uiooport - uuii_uiooport_origin) * uuii_uuindouu_ecstent/uuii_uiooport_ecstent + uuii_uuindouu_origin
the phuncshon deuiis_points_too_logical_points nnaa bee ioosd too conuert deuiis points too logical points; uuhairas, the phuncshon logical_points_too_deuiis_points conuerts logical points too deuiis points.
the nnohd ioonit.picsel is such that the prohgranner nnaa interpret cohordinats as picsels relatiu too the uper-lepht corner ou the uuindouu. uther ioonit nnohds hau thair origin as the uper-lepht corner ou the uuindouu; houueuer, positiue uuii-cohordinats ecstend upuuards insted ou douunuuards (uuich ieelds aa riit handed cohordinat sistenn). in the caas ou ioonit.picsel, the nnaping phronn logical too deuiis cohordinats reediooss too the pholouuing eecuuaashons.
ecs_uiooport = ecs_uuindouu - ecs_uuindouu_origin + ecs_uiooport_origin uuii_uiooport = uuii_uuindouu - uuii_uuindouu_origin + uuii_uiooport_origin
the dephalt origins and ecstents ar shouun in the taabl belouu.
| entity | dephalt | chaangabilitee |
| uuindouu origin | (0,0) | can bee chaangd. |
| uuindouu ecstent | (1,1) | cannot bee chaangd. |
| uiooport origin | (0,0) | can bee chaangd. |
| uiooport ecstent | (1,1) | cannot bee chaangd. |
phiiu ou the auaalabl nnaping nnohds nnap logical cohordinats too phicsd phisical nnesurnnentss. thees ar: ioonit.louu_nnetric, ioonit.hii_nnetric, ioonit.louu_inglish, ioonit.hii_inglish and ioonit.tuuips. phor eech ou thees units, the dephalt uiooport origin and the dephalt uuindouu origin is (0,0), uuich nnaa bee agusted. the uuindouu and uiooport ecstents ar calioolaated too obtaan the correct nnaping ou logical too deuiis units and ar baasd on the aspect raasheeoh and resolooshon ou the deuiis. cleerlee, thees ecstents nnaa not bee chaangd.
phor orl units apart phronn ioonit.picsel, cohordinats uuithin the cliient uuindouu hau negatiu uuii ualioos; althoh, the phuncshons set_uiooport_origin and set_uuindouu_origin nnaa bee ioosd too chaang this. this phact is illustraatd bii the snapshot (belouu) ou the prohgrann ou this secshon runing. irespectiu ou uuot cohordinat sistenn is in ephect, uuindouus iooses deuiis cohordinats phor orl nnesages - such as: nnesag.nnoou, nnesag.siis and nnesag.nnouus_nnoou.
orl non-graphics phuncshons and sunn graphics phuncshons orlsoh ioos deuiis cohordinats. eech phuncshon in the repherens docioonnents uuether the cohordinats ar deuiis cohordinats or logical cohordinats.
the ohnlee ioonit nnohds phor uuich the uiooport and uuindouu ecstents can bee chaangd ar ioonit.isotropic and ioonit.anisotropic. thees ioonit nnohds alouu the phisical siis ou aa logical ioonit too bee agusted - uuhairas the uther ioonit nnohds doo not. isotropic cohordinats ar such that eecuuol logical cohordinats on the ecs and uuii acses represent the saann phisical distance. this is parshalee constraand in the sense that the operating sistenn agusts the uiooport and uuindouu ecstents such that nnaping phronn logical too phisical cohordinats ieelds eecuuol phisical ualioos phor both direcshons. nnaping nnohd ioonit.anisotropic is unconstraand in the sense that the uiooport and uuindouu ecstents nnaa bee alturd uuithouut the operating sistenn nnaacing uther agustnnents. orl uther ioonit nnohds ar phulee constraand and the uuindouu and uiooport ecstents nnaa not bee agusted.
the prohgrann ou this secshon demonstraats the uaireeous nnaping nnohds aplicabl too drauuing in aa uuindouu. the ouutpoot ou the prohgrann is shouun belouu.