## wxDC

A wxDC is a device context onto which graphics and text can be drawn. It is intended to represent a number of output devices in a generic way, so a window can have a device context associated with it, and a printer also has a device context. In this way, the same piece of code may write to a number of different devices, if the device context is used as a parameter.

Derived types of wxDC have documentation for specific features only, so refer to this section for most device context information.

Derived from

wxObject

Include files

<wx/dc.h>

See also

Overview

Members

wxDC::wxDC
wxDC::~wxDC
wxDC::BeginDrawing
wxDC::Blit
wxDC::CalcBoundingBox
wxDC::Clear
wxDC::CrossHair
wxDC::DestroyClippingRegion
wxDC::DeviceToLogicalX
wxDC::DeviceToLogicalXRel
wxDC::DeviceToLogicalY
wxDC::DeviceToLogicalYRel
wxDC::DrawArc
wxDC::DrawBitmap
wxDC::DrawCheckMark
wxDC::DrawEllipse
wxDC::DrawEllipticArc
wxDC::DrawIcon
wxDC::DrawLine
wxDC::DrawLines
wxDC::DrawPolygon
wxDC::DrawPoint
wxDC::DrawRectangle
wxDC::DrawRotatedText
wxDC::DrawRoundedRectangle
wxDC::DrawSpline
wxDC::DrawText
wxDC::EndDoc
wxDC::EndDrawing
wxDC::EndPage
wxDC::FloodFill
wxDC::GetBackground
wxDC::GetBackgroundMode
wxDC::GetBrush
wxDC::GetCharHeight
wxDC::GetCharWidth
wxDC::GetClippingBox
wxDC::GetFont
wxDC::GetLogicalFunction
wxDC::GetMapMode
wxDC::GetOptimization
wxDC::GetPen
wxDC::GetPixel
wxDC::GetSize
wxDC::GetTextBackground
wxDC::GetTextExtent
wxDC::GetTextForeground
wxDC::GetUserScale
wxDC::LogicalToDeviceX
wxDC::LogicalToDeviceXRel
wxDC::LogicalToDeviceY
wxDC::LogicalToDeviceYRel
wxDC::MaxX
wxDC::MaxY
wxDC::MinX
wxDC::MinY
wxDC::Ok
wxDC::ResetBoundingBox
wxDC::SetDeviceOrigin
wxDC::SetBackground
wxDC::SetBackgroundMode
wxDC::SetClippingRegion
wxDC::SetPalette
wxDC::SetBrush
wxDC::SetFont
wxDC::SetLogicalFunction
wxDC::SetMapMode
wxDC::SetOptimization
wxDC::SetPen
wxDC::SetTextBackground
wxDC::SetTextForeground
wxDC::SetUserScale
wxDC::StartDoc
wxDC::StartPage

### wxDC::wxDC

wxDC()

Constructor.

### wxDC::~wxDC

~wxDC()

Destructor.

### wxDC::BeginDrawing

void BeginDrawing()

Allows optimization of drawing code under MS Windows. Enclose drawing primitives between BeginDrawing and EndDrawing calls.

Drawing to a wxDialog panel device context outside of a system-generated OnPaint event requires this pair of calls to enclose drawing code. This is because a Windows dialog box does not have a retained device context associated with it, and selections such as pen and brush settings would be lost if the device context were obtained and released for each drawing operation.

### wxDC::Blit

bool Blit(wxCoord xdest, wxCoord ydest, wxCoord width, wxCoord height, wxDC* source, wxCoord xsrc, wxCoord ysrc, int logicalFunc = wxCOPY, bool useMask = FALSE)

Copy from a source DC to this DC, specifying the destination coordinates, size of area to copy, source DC, source coordinates, and logical function.

Parameters

xdest

Destination device context x position.

ydest

Destination device context y position.

width

Width of source area to be copied.

height

Height of source area to be copied.

source

Source device context.

xsrc

Source device context x position.

ysrc

Source device context y position.

logicalFunc

Logical function to use: see wxDC::SetLogicalFunction.

useMask

If TRUE, Blit does a transparent blit using the mask that is associated with the bitmap selected into the source device context. The Windows implementation does the following:

1. Creates a temporary bitmap and copies the destination area into it.
2. Copies the source area into the temporary bitmap using the specified logical function.
3. Sets the masked area in the temporary bitmap to BLACK by ANDing the mask bitmap with the temp bitmap with the foreground colour set to WHITE and the bg colour set to BLACK.
4. Sets the unmasked area in the destination area to BLACK by ANDing the mask bitmap with the destination area with the foreground colour set to BLACK and the background colour set to WHITE.
5. ORs the temporary bitmap with the destination area.
6. Deletes the temporary bitmap.

This sequence of operations ensures that the source's transparent area need not be black, and logical functions are supported.

Remarks

There is partial support for Blit in wxPostScriptDC, under X.

See wxMemoryDC for typical usage.

See also

wxMemoryDC, wxBitmap, wxMask

### wxDC::CalcBoundingBox

void CalcBoundingBox(wxCoord x, wxCoord y)

Adds the specified point to the bounding box which can be retrieved with MinX, MaxX and MinY, MaxY functions.

See also

ResetBoundingBox

### wxDC::Clear

void Clear()

Clears the device context using the current background brush.

### wxDC::CrossHair

void CrossHair(wxCoord x, wxCoord y)

Displays a cross hair using the current pen. This is a vertical and horizontal line the height and width of the window, centred on the given point.

### wxDC::DestroyClippingRegion

void DestroyClippingRegion()

Destroys the current clipping region so that none of the DC is clipped. See also wxDC::SetClippingRegion.

### wxDC::DeviceToLogicalX

wxCoord DeviceToLogicalX(wxCoord x)

Convert device X coordinate to logical coordinate, using the current mapping mode.

### wxDC::DeviceToLogicalXRel

wxCoord DeviceToLogicalXRel(wxCoord x)

Convert device X coordinate to relative logical coordinate, using the current mapping mode. Use this function for converting a width, for example.

### wxDC::DeviceToLogicalY

wxCoord DeviceToLogicalY(wxCoord y)

Converts device Y coordinate to logical coordinate, using the current mapping mode.

### wxDC::DeviceToLogicalYRel

wxCoord DeviceToLogicalYRel(wxCoord y)

Convert device Y coordinate to relative logical coordinate, using the current mapping mode. Use this function for converting a height, for example.

### wxDC::DrawArc

void DrawArc(wxCoord x1, wxCoord y1, wxCoord x2, wxCoord y2, double xc, double yc)

Draws an arc of a circle, centred on (xc, yc), with starting point (x1, y1) and ending at (x2, y2). The current pen is used for the outline and the current brush for filling the shape.

The arc is drawn in an anticlockwise direction from the start point to the end point.

### wxDC::DrawBitmap

void DrawBitmap(const wxBitmap& bitmap, wxCoord x, wxCoord y, bool transparent)

Draw a bitmap on the device context at the specified point. If transparent is TRUE and the bitmap has a transparency mask, the bitmap will be drawn transparently.

When drawing a mono-bitmap, the current text foreground colour will be used to draw the foreground of the bitmap (all bits set to 1), and the current text background colour to draw the background (all bits set to 0). See also SetTextForeground, SetTextBackground and wxMemoryDC.

### wxDC::DrawCheckMark

void DrawCheckMark(wxCoord x, wxCoord y, wxCoord width, wxCoord height)

void DrawCheckMark(const wxRect &rect)

Draws a check mark inside the given rectangle.

### wxDC::DrawEllipse

void DrawEllipse(wxCoord x, wxCoord y, wxCoord width, wxCoord height)

Draws an ellipse contained in the rectangle with the given top left corner, and with the given size. The current pen is used for the outline and the current brush for filling the shape.

### wxDC::DrawEllipticArc

void DrawEllipticArc(wxCoord x, wxCoord y, wxCoord width, wxCoord height, double start, double end)

Draws an arc of an ellipse. The current pen is used for drawing the arc and the current brush is used for drawing the pie.

x and y specify the x and y coordinates of the upper-left corner of the rectangle that contains the ellipse.

width and height specify the width and height of the rectangle that contains the ellipse.

start and end specify the start and end of the arc relative to the three-o'clock position from the center of the rectangle. Angles are specified in degrees (360 is a complete circle). Positive values mean counter-clockwise motion. If start is equal to end, a complete ellipse will be drawn.

### wxDC::DrawIcon

void DrawIcon(const wxIcon& icon, wxCoord x, wxCoord y)

Draw an icon on the display (does nothing if the device context is PostScript). This can be the simplest way of drawing bitmaps on a window.

### wxDC::DrawLine

void DrawLine(wxCoord x1, wxCoord y1, wxCoord x2, wxCoord y2)

Draws a line from the first point to the second. The current pen is used for drawing the line.

### wxDC::DrawLines

void DrawLines(int n, wxPoint points[], wxCoord xoffset = 0, wxCoord yoffset = 0)

void DrawLines(wxList *points, wxCoord xoffset = 0, wxCoord yoffset = 0)

Draws lines using an array of points of size n, or list of pointers to points, adding the optional offset coordinate. The current pen is used for drawing the lines. The programmer is responsible for deleting the list of points.

wxPython note: The wxPython version of this method accepts a Python list of wxPoint objects.

### wxDC::DrawPolygon

void DrawPolygon(int n, wxPoint points[], wxCoord xoffset = 0, wxCoord yoffset = 0,
int fill_style = wxODDEVEN_RULE)

void DrawPolygon(wxList *points, wxCoord xoffset = 0, wxCoord yoffset = 0,
int fill_style = wxODDEVEN_RULE)

Draws a filled polygon using an array of points of size n, or list of pointers to points, adding the optional offset coordinate.

The last argument specifies the fill rule: wxODDEVEN_RULE (the default) or wxWINDING_RULE.

The current pen is used for drawing the outline, and the current brush for filling the shape. Using a transparent brush suppresses filling. The programmer is responsible for deleting the list of points.

Note that wxWindows automatically closes the first and last points.

wxPython note: The wxPython version of this method accepts a Python list of wxPoint objects.

### wxDC::DrawPoint

void DrawPoint(wxCoord x, wxCoord y)

Draws a point using the current pen.

### wxDC::DrawRectangle

void DrawRectangle(wxCoord x, wxCoord y, wxCoord width, wxCoord height)

Draws a rectangle with the given top left corner, and with the given size. The current pen is used for the outline and the current brush for filling the shape.

### wxDC::DrawRotatedText

void DrawRotatedText(const wxString& text, wxCoord x, wxCoord y, double angle)

Draws the text rotated by angle degrees.

See also

DrawText

### wxDC::DrawRoundedRectangle

void DrawRoundedRectangle(wxCoord x, wxCoord y, wxCoord width, wxCoord height, double radius = 20)

Draws a rectangle with the given top left corner, and with the given size. The corners are quarter-circles using the given radius. The current pen is used for the outline and the current brush for filling the shape.

If radius is positive, the value is assumed to be the radius of the rounded corner. If radius is negative, the absolute value is assumed to be the proportion of the smallest dimension of the rectangle. This means that the corner can be a sensible size relative to the size of the rectangle, and also avoids the strange effects X produces when the corners are too big for the rectangle.

### wxDC::DrawSpline

void DrawSpline(wxList *points)

Draws a spline between all given control points, using the current pen. Doesn't delete the wxList and contents. The spline is drawn using a series of lines, using an algorithm taken from the X drawing program 'XFIG'.

void DrawSpline(wxCoord x1, wxCoord y1, wxCoord x2, wxCoord y2, wxCoord x3, wxCoord y3)

Draws a three-point spline using the current pen.

wxPython note: The wxPython version of this method accepts a Python list of wxPoint objects.

### wxDC::DrawText

void DrawText(const wxString& text, wxCoord x, wxCoord y)

Draws a text string at the specified point, using the current text font, and the current text foreground and background colours.

The coordinates refer to the top-left corner of the rectangle bounding the string. See wxDC::GetTextExtent for how to get the dimensions of a text string, which can be used to position the text more precisely.

NB: under wxGTK the current logical function is used by this function but it is ignored by wxMSW. Thus, you should avoid using logical functions with this function in portable programs.

### wxDC::EndDoc

void EndDoc()

Ends a document (only relevant when outputting to a printer).

### wxDC::EndDrawing

void EndDrawing()

Allows optimization of drawing code under MS Windows. Enclose drawing primitives between BeginDrawing and EndDrawing calls.

### wxDC::EndPage

void EndPage()

Ends a document page (only relevant when outputting to a printer).

### wxDC::FloodFill

void FloodFill(wxCoord x, wxCoord y, const wxColour& colour, int style=wxFLOOD_SURFACE)

Flood fills the device context starting from the given point, using the current brush colour, and using a style:

- wxFLOOD_SURFACE: the flooding occurs until a colour other than the given colour is encountered.
- wxFLOOD_BORDER: the area to be flooded is bounded by the given colour.

Note: this function is available in MS Windows only.

### wxDC::GetBackground

wxBrush& GetBackground()

const wxBrush& GetBackground() const

Gets the brush used for painting the background (see wxDC::SetBackground).

### wxDC::GetBackgroundMode

int GetBackgroundMode() const

Returns the current background mode: `wxSOLID` or `wxTRANSPARENT`.

See also

SetBackgroundMode

### wxDC::GetBrush

wxBrush& GetBrush()

const wxBrush& GetBrush() const

Gets the current brush (see wxDC::SetBrush).

### wxDC::GetCharHeight

wxCoord GetCharHeight()

Gets the character height of the currently set font.

### wxDC::GetCharWidth

wxCoord GetCharWidth()

Gets the average character width of the currently set font.

### wxDC::GetClippingBox

void GetClippingBox(wxCoord *x, wxCoord *y, wxCoord *width, wxCoord *height)

Gets the rectangle surrounding the current clipping region.

wxPython note: No arguments are required and the four values defining the rectangle are returned as a tuple.

### wxDC::GetFont

wxFont& GetFont()

const wxFont& GetFont() const

Gets the current font (see wxDC::SetFont).

### wxDC::GetLogicalFunction

int GetLogicalFunction()

Gets the current logical function (see wxDC::SetLogicalFunction).

### wxDC::GetMapMode

int GetMapMode()

Gets the mapping mode for the device context (see wxDC::SetMapMode).

### wxDC::GetOptimization

bool GetOptimization()

Returns TRUE if device context optimization is on. See wxDC::SetOptimization for details.

### wxDC::GetPen

wxPen& GetPen()

const wxPen& GetPen() const

Gets the current pen (see wxDC::SetPen).

### wxDC::GetPixel

bool GetPixel(wxCoord x, wxCoord y, wxColour *colour)

Sets colour to the colour at the specified location. Windows only; an X implementation is being worked on. Not available for wxPostScriptDC or wxMetafileDC.

wxPython note: For wxPython the wxColour value is returned and is not required as a parameter.

### wxDC::GetSize

void GetSize(wxCoord *width, wxCoord *height)

For a PostScript device context, this gets the maximum size of graphics drawn so far on the device context.

For a Windows printer device context, this gets the horizontal and vertical resolution. It can be used to scale graphics to fit the page when using a Windows printer device context. For example, if maxX and maxY represent the maximum horizontal and vertical 'pixel' values used in your application, the following code will scale the graphic to fit on the printer page:

      wxCoord w, h;
      dc.GetSize(&w, &h);
      double scaleX=(double)(maxX/w);
      double scaleY=(double)(maxY/h);
      dc.SetUserScale(min(scaleX,scaleY),min(scaleX,scaleY));

wxPython note: In place of a single overloaded method name, wxPython implements the following methods:

GetSize() | Returns a wxSize
GetSizeTuple() | Returns a 2-tuple (width, height)

### wxDC::GetTextBackground

wxColour& GetTextBackground()

const wxColour& GetTextBackground() const

Gets the current text background colour (see wxDC::SetTextBackground).

### wxDC::GetTextExtent

void GetTextExtent(const wxString& string, wxCoord *w, wxCoord *h,
wxCoord *descent = NULL, wxCoord *externalLeading = NULL, wxFont *font = NULL)

Gets the dimensions of the string using the currently selected font. string is the text string to measure, w and h are the total width and height respectively, descent is the dimension from the baseline of the font to the bottom of the descender, and externalLeading is any extra vertical space added to the font by the font designer (usually is zero).

The optional parameter font specifies an alternative to the currently selected font: but note that this does not yet work under Windows, so you need to set a font for the device context first.

See also wxFont, wxDC::SetFont.

wxPython note: The following methods are implemented in wxPython:

GetTextExtent(string) | Returns a 2-tuple, (width, height)
GetFullTextExtent(string, font=NULL) | Returns a 4-tuple, (width, height, descent, externalLeading)

### wxDC::GetTextForeground

wxColour& GetTextForeground()

const wxColour& GetTextForeground() const

Gets the current text foreground colour (see wxDC::SetTextForeground).

### wxDC::GetUserScale

void GetUserScale(double *x, double *y)

Gets the current user scale factor (set by SetUserScale).

### wxDC::LogicalToDeviceX

wxCoord LogicalToDeviceX(wxCoord x)

Converts logical X coordinate to device coordinate, using the current mapping mode.

### wxDC::LogicalToDeviceXRel

wxCoord LogicalToDeviceXRel(wxCoord x)

Converts logical X coordinate to relative device coordinate, using the current mapping mode. Use this for converting a width, for example.

### wxDC::LogicalToDeviceY

wxCoord LogicalToDeviceY(wxCoord y)

Converts logical Y coordinate to device coordinate, using the current mapping mode.

### wxDC::LogicalToDeviceYRel

wxCoord LogicalToDeviceYRel(wxCoord y)

Converts logical Y coordinate to relative device coordinate, using the current mapping mode. Use this for converting a height, for example.

### wxDC::MaxX

wxCoord MaxX()

Gets the maximum horizontal extent used in drawing commands so far.

### wxDC::MaxY

wxCoord MaxY()

Gets the maximum vertical extent used in drawing commands so far.

### wxDC::MinX

wxCoord MinX()

Gets the minimum horizontal extent used in drawing commands so far.

### wxDC::MinY

wxCoord MinY()

Gets the minimum vertical extent used in drawing commands so far.

### wxDC::Ok

bool Ok()

Returns TRUE if the DC is ok to use.

### wxDC::ResetBoundingBox

void ResetBoundingBox()

Resets the bounding box: after a call to this function, the bounding box doesn't contain anything.

See also

CalcBoundingBox

### wxDC::SetDeviceOrigin

void SetDeviceOrigin(wxCoord x, wxCoord y)

Sets the device origin (i.e., the origin in pixels after scaling has been applied).

This function may be useful in Windows printing operations for placing a graphic on a page.

### wxDC::SetBackground

void SetBackground(const wxBrush& brush)

Sets the current background brush for the DC.

### wxDC::SetBackgroundMode

void SetBackgroundMode(int mode)

mode may be one of wxSOLID and wxTRANSPARENT. This setting determines whether text will be drawn with a background colour or not.

### wxDC::SetClippingRegion

void SetClippingRegion(wxCoord x, wxCoord y, wxCoord width, wxCoord height)

void SetClippingRegion(const wxRegion& region)

Sets the clipping region for the DC. The clipping region is an area to which drawing is restricted. Possible uses for the clipping region are for clipping text or for speeding up window redraws when only a known area of the screen is damaged.

See also

wxDC::DestroyClippingRegion, wxRegion

### wxDC::SetPalette

void SetPalette(const wxPalette& palette)

If this is a window DC or memory DC, assigns the given palette to the window or bitmap associated with the DC. If the argument is wxNullPalette, the current palette is selected out of the device context, and the original palette restored.

See wxPalette for further details.

### wxDC::SetBrush

void SetBrush(const wxBrush& brush)

Sets the current brush for the DC.

If the argument is wxNullBrush, the current brush is selected out of the device context, and the original brush restored, allowing the current brush to be destroyed safely.

See also wxBrush.

See also wxMemoryDC for the interpretation of colours when drawing into a monochrome bitmap.

### wxDC::SetFont

void SetFont(const wxFont& font)

Sets the current font for the DC.

If the argument is wxNullFont, the current font is selected out of the device context, and the original font restored, allowing the current font to be destroyed safely.

See also wxFont.

### wxDC::SetLogicalFunction

void SetLogicalFunction(int function)

Sets the current logical function for the device context. This determines how a source pixel (from a pen or brush colour, or source device context if using wxDC::Blit) combines with a destination pixel in the current device context.

The possible values and their meaning in terms of source and destination pixel values are as follows:

    wxAND                 src AND dst
    wxAND_INVERT          (NOT src) AND dst
    wxAND_REVERSE         src AND (NOT dst)
    wxCLEAR               0
    wxCOPY                src
    wxEQUIV               (NOT src) XOR dst
    wxINVERT              NOT dst
    wxNAND                (NOT src) OR (NOT dst)
    wxNOR                 (NOT src) AND (NOT dst)
    wxNO_OP               dst
    wxOR                  src OR dst
    wxOR_INVERT           (NOT src) OR dst
    wxOR_REVERSE          src OR (NOT dst)
    wxSET                 1
    wxSRC_INVERT          NOT src
    wxXOR                 src XOR dst

The default is wxCOPY, which simply draws with the current colour. The others combine the current colour and the background using a logical operation. wxINVERT is commonly used for drawing rubber bands or moving outlines, since drawing twice reverts to the original colour.

### wxDC::SetMapMode

void SetMapMode(int int)

The mapping mode of the device context defines the unit of measurement used to convert logical units to device units. Note that in X, text drawing isn't handled consistently with the mapping mode; a font is always specified in point size. However, setting the user scale (see wxDC::SetUserScale) scales the text appropriately. In Windows, scaleable TrueType fonts are always used; in X, results depend on availability of fonts, but usually a reasonable match is found.

Note that the coordinate origin should ideally be selectable, but for now is always at the top left of the screen/printer.

Drawing to a Windows printer device context under UNIX uses the current mapping mode, but mapping mode is currently ignored for PostScript output.

The mapping mode can be one of the following:

wxMM_TWIPS | Each logical unit is 1/20 of a point, or 1/1440 of an inch.
wxMM_POINTS | Each logical unit is a point, or 1/72 of an inch.
wxMM_METRIC | Each logical unit is 1 mm.
wxMM_LOMETRIC | Each logical unit is 1/10 of a mm.
wxMM_TEXT | Each logical unit is 1 pixel.

### wxDC::SetOptimization

void SetOptimization(bool optimize)

If optimize is TRUE (the default), this function sets optimization mode on. This currently means that under X, the device context will not try to set a pen or brush property if it is known to be set already. This approach can fall down if non-wxWindows code is using the same device context or window, for example when the window is a panel on which the windowing system draws panel items. The wxWindows device context 'memory' will now be out of step with reality.

Setting optimization off, drawing, then setting it back on again, is a trick that must occasionally be employed.

### wxDC::SetPen

void SetPen(const wxPen& pen)

Sets the current pen for the DC.

If the argument is wxNullPen, the current pen is selected out of the device context, and the original pen restored.

See also wxMemoryDC for the interpretation of colours when drawing into a monochrome bitmap.

### wxDC::SetTextBackground

void SetTextBackground(const wxColour& colour)

Sets the current text background colour for the DC.

### wxDC::SetTextForeground

void SetTextForeground(const wxColour& colour)

Sets the current text foreground colour for the DC.

See also wxMemoryDC for the interpretation of colours when drawing into a monochrome bitmap.

### wxDC::SetUserScale

void SetUserScale(double xScale, double yScale)

Sets the user scaling factor, useful for applications which require 'zooming'.

### wxDC::StartDoc

bool StartDoc(const wxString& message)

Starts a document (only relevant when outputting to a printer). Message is a message to show whilst printing.

### wxDC::StartPage

bool StartPage()

Starts a document page (only relevant when outputting to a printer).