PCS Lecture

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LECTURE 7

• Mapping Modes
• System Metrics
• Other Topics

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MAPPING MODES

• What are mapping Modes?
• We have seen that the device context holds the
  current GDI information and effects how we draw
  onto a device.

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But the Screen is not the WORLD

• The screen co-ordinate system is Pixels
• The world may use Inchs, Centimeters or any other
  specific dimension

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Windows Dimensions and View

• Windows Origin
• Viewport Origin
• Windows Extent
• Viewport Extent
• From these three criteria sets of information
  we can derive a Mapping Mode.

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Logical Units

• Textout (hdc,x,y,Buffer,length)
• The X and Y are positions for the start of the
  text. - these positions are Logical Units
• Windows has to translate Logical Units to Device
  Units
• This translation is governed by the selected
  mapping mode in the device context.

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Map Modes

• Mode Logical Unit X axis Y axis
• MM_TEXT Pixel Right Down
• MM_LOMETRIC 0.1 mm Right Up
• MM_HIMETRIC 0.01 mm Right Up
• MM_LOENGLISH 0.01 inch Right Up
• MM_HIENGLISH 0.001 inch Right Up
• MM_TWIPS 1/1440 inch Right Up
• MM_ISOTROPIC Arb x y Select Select
• MM_ANISOTROPIC Arb x ! y Select Select

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MAP MODE SET UP

• You can set map Mode simple by SetMapMode(hdc,
  mode)
• Regardless of the map mode selected X and y must
  be short integers i.e. -32767 to 32768.
• This is true even in 32 but Windows !

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Device Coordinates and Logical Coordinates

• You must not get confused by map modes,
• If you set MM_LOENGLISH you will not get WM_SIZE
  messages with the screen rectangle quoted in
  hundredths of an inch!

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Device Coordinate System

• Windows maps the logical coordinates in GDI
  functions to device coordinates via the Map Mode
  defined.
• In a video system the device coordinates are
  always in Pixels.

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Device Definitions
Screen 0,0

Window 0,0
Client 0,0
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Client to Screen etc.

• Various APIs exist to convert and get
  Coordinates
• ClientToScreen
• ScreenToClient
• GetWindowRect
• GetClientRect

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Viewport and the Window

• Using the mapping mode we are defining how the
  logical coordinates are mapped to the device
  coordinates..
• In most cases in windows the viewport is the same
  as the client area of the window itself, however
  in some cases it can be related to the window
  coordinates themselves.

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MM_TEXT (Default)

• SetViewportOrg (hdc, cxClient / 2, cyClient /2)

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A Little Strange !

• As another option we could move the origin as
• SetViewportOrg (hdc,cxClient /2 , cyClient /2)
• SetWindowOrg (hdc, -cxClient /2, -cyClient /2)

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Basic Dimension of Mapping

• The default for LO and HI English and LO and HI
  Metric are
• Window Origin (0,0) - Can be changed
• Viewport Origin (0,0) - Can Be Changed
• Window extent (?,?) - Cannot be changed
• Viewport extent (?,?) - Cannot be changed

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MAKE YOUR OWN MAP MODE

• MM_ISOTROPIC
• MM_ANISOTROPIC
• allow you to change the viewport and windows
  extent meaning that we have an ability to change
  scaling.
• ISOTROPIC means same in both directions i.e. x
  y
• ANISOTROPIC different in both directions i.e. x
  ! y.

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ISOTROPIC

• ISOTROPIC
• define arbitrary axes
• preserving equal logical units
• rectangles with equal sides squares
• ellipses with equal major and minor axis
  circles.

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GetTextMetrics

• struct _TEXTMETRIC
• Some standard calculations ...
• Character Width normal tmAveCharWidth
• Capital Character Width (tmPitchAndFamily 1)
  ? 3 2))Character Width normal
• Character Height tmHeight tmExternalLeading

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SCROLL TECHNIQUES

• Normally any window which displays text will have
  scroll bars.
• Need to calculate the range of the scroll and the
  scroll position etc.
• We will only look at Vertical scroll control,
• Similar argument can be applied to Horizontal
  scroll and the same technique can be employed.

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STANDARD Macro's

• define min(a,b) (((a) lt (b)) ? (a) (b))
• define max(a,b) (((a) gt (b)) ? (a) (b))
• SCROLL APIs
• SetScrollRange (.....)
• SetScrollPosition(....)

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TYPICAL WM_CREATE

• hdc GetDC (hwnd) // can't do TextMetrics
  etc. without a Device Context.
• GetTextMetrics (hdc, tm)
• cxChar tm.tmAveCharWidth
• cxCaps (tm.tmPitchAndFamily 1 ? 3 2)
  cxChar/2
• cyChar tm.tmHeight tm.tmExternalLeading
• ReleaseDC (hwnd, hdc)
• nMaxWidth 40 cxChar 22 cxCaps // Thats
  a
• // typical setting for max width on a line

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TYPICAL in WM_SIZE

• cxClient LOWORD (lParam) // can extract the
  client size
• // from the parameters.
• cyClient HIWORD (lParam)
• nVscrollMax max (0, NUMLINES 2 - cyClient /
  cyChar)
• // NUMLINES is how many display lines
• nVscrollPos min (nVscrollPos, nVscrollMax)
• SetScrollRange (hwnd, SB_VERT, 0, nVscrollMax,
  FALSE)
• SetScrollPos (hwnd, SB_VERT, nVscrollPos, TRUE)
  
• nHscrollMax max (0, 2 (nMaxWidth - cxClient)
  / cxChar)
• nHscrollPos min (nHscrollPos, nHscrollMax)
• SetScrollRange (hwnd, SB_HORZ, 0, nHscrollMax,
  FALSE)
• SetScrollPos (hwnd, SB_HORZ, nHscrollPos, TRUE)
  

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Device Caps

• This allows you to determine Physical
  capabilities of the device.
• GetDeviceCaps(...)
• Typical Devices (hdc)
• DT_PLOTTER Vector plotter
• DT_RASDISPLAY Raster display
• DT_RASPRINTER Raster printer
• DT_RASCAMERA Raster camera
• DT_CHARSTREAM Character stream
• DT_METAFILE Metafile
• DT_DISPFILE Display file

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Characteristics

• Typical values
• HORZSIZE Width, in millimeters, of the physical
  screen.
• VERTSIZE Height, in millimeters, of the physical
  screen.
• HORZRES Width, in pixels, of the screen.
• VERTRES Height, in raster lines, of the screen.
• LOGPIXELSX Number of pixels per logical inch
  along the screen width.
• LOGPIXELSYNumber of pixels per logical inch along
  the screen height.
• BITSPIXEL Number of adjacent color bits for each
  pixel.