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.
Please note that in addition to the versions of the methods documented here, there are also versions which accept single wxPoint parameter instead of two wxCoord ones or wxPoint and wxSize instead of four of them.
Derived from
Include files
<wx/dc.h>
See also
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::DrawCircle
wxDC::DrawEllipse
wxDC::DrawEllipticArc
wxDC::DrawIcon
wxDC::DrawLine
wxDC::DrawLines
wxDC::DrawPolygon
wxDC::DrawPolyPolygon
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::GetPartialTextExtents
wxDC::GetPen
wxDC::GetPixel
wxDC::GetPPI
wxDC::GetSize
wxDC::GetSizeMM
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::SetAxisOrientation
wxDC::SetBackground
wxDC::SetBackgroundMode
wxDC::SetBrush
wxDC::SetClippingRegion
wxDC::SetDeviceOrigin
wxDC::SetFont
wxDC::SetLogicalFunction
wxDC::SetMapMode
wxDC::SetOptimization
wxDC::SetPalette
wxDC::SetPen
wxDC::SetTextBackground
wxDC::SetTextForeground
wxDC::SetUserScale
wxDC::StartDoc
wxDC::StartPage
wxDC()
Constructor.
~wxDC()
Destructor.
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.
bool Blit(wxCoord xdest, wxCoord ydest, wxCoord width, wxCoord height, wxDC* source, wxCoord xsrc, wxCoord ysrc, int logicalFunc = wxCOPY, bool useMask = false, wxCoord xsrcMask = -1, wxCoord ysrcMask = -1)
Copy from a source DC to this DC, specifying the destination coordinates, size of area to copy, source DC, source coordinates, logical function, whether to use a bitmap mask, and mask source position.
Parameters
xdest
ydest
width
height
source
xsrc
ysrc
logicalFunc
useMask
This sequence of operations ensures that the source's transparent area need not be black, and logical functions are supported.
Note: on Windows, blitting with masks can be speeded up considerably by compiling wxWidgets with the wxUSE_DC_CACHE option enabled. You can also influence whether MaskBlt or the explicit mask blitting code above is used, by using wxSystemOptions and setting the no-maskblt option to 1.
xsrcMask
ysrcMask
Remarks
There is partial support for Blit in wxPostScriptDC, under X.
See wxMemoryDC for typical usage.
See also
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
void Clear()
Clears the device context using the current background brush.
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.
void DestroyClippingRegion()
Destroys the current clipping region so that none of the DC is clipped. See also wxDC::SetClippingRegion.
wxCoord DeviceToLogicalX(wxCoord x)
Convert device X coordinate to logical coordinate, using the current mapping mode.
wxCoord DeviceToLogicalXRel(wxCoord x)
Convert device X coordinate to relative logical coordinate, using the current mapping mode but ignoring the x axis orientation. Use this function for converting a width, for example.
wxCoord DeviceToLogicalY(wxCoord y)
Converts device Y coordinate to logical coordinate, using the current mapping mode.
wxCoord DeviceToLogicalYRel(wxCoord y)
Convert device Y coordinate to relative logical coordinate, using the current mapping mode but ignoring the y axis orientation. Use this function for converting a height, for example.
void DrawArc(wxCoord x1, wxCoord y1, wxCoord x2, wxCoord y2, wxCoord xc, wxCoord 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.
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.
void DrawCheckMark(wxCoord x, wxCoord y, wxCoord width, wxCoord height)
void DrawCheckMark(const wxRect &rect)
Draws a check mark inside the given rectangle.
void DrawCircle(wxCoord x, wxCoord y, wxCoord radius)
void DrawCircle(const wxPoint& pt, wxCoord radius)
Draws a circle with the given centre and radius.
See also
void DrawEllipse(wxCoord x, wxCoord y, wxCoord width, wxCoord height)
void DrawEllipse(const wxPoint& pt, const wxSize& size)
void DrawEllipse(const wxRect& rect)
Draws an ellipse contained in the rectangle specified either with the given top left corner and the given size or directly. The current pen is used for the outline and the current brush for filling the shape.
See also
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.
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.
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. Note that the point (x2, y2) is not part of the line and is not drawn by this function (this is consistent with the behaviour of many other toolkits).
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.
wxPerl note: The wxPerl version of this method accepts as its first parameter a reference to an array of wxPoint objects.
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 wxWidgets automatically closes the first and last points.
wxPython note: The wxPython version of this method accepts a Python list of wxPoint objects.
wxPerl note: The wxPerl version of this method accepts as its first parameter a reference to an array of wxPoint objects.
void DrawPolyPolygon(int n, int count[], wxPoint points[], wxCoord xoffset = 0, wxCoord yoffset = 0,
int fill_style = wxODDEVEN_RULE)
Draws two or more filled polygons using an array of points, adding the optional offset coordinates.
Notice that for the platforms providing a native implementation of this function (Windows and PostScript-based wxDC currently), this is more efficient than using DrawPolygon in a loop.
n specifies the number of polygons to draw, the array count of size n specifies the number of points in each of the polygons in the points array.
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 polygons maybe disjoint or overlapping. Each polygon specified in a call to DrawPolyPolygon must be closed. Unlike polygons created by the DrawPolygon member function, the polygons created by DrawPolyPolygon are not closed automatically.
wxPython note: Not implemented yet
wxPerl note: Not implemented yet
void DrawPoint(wxCoord x, wxCoord y)
Draws a point using the color of the current pen. Note that the other properties of the pen are not used, such as width etc..
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.
void DrawRotatedText(const wxString& text, wxCoord x, wxCoord y, double angle)
Draws the text rotated by angle degrees.
NB: Under Win9x only TrueType fonts can be drawn by this function. In particular, a font different from wxNORMAL_FONT should be used as the latter is not a TrueType font. wxSWISS_FONT is an example of a font which is.
See also
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.
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.
wxPerl note: The wxPerl version of this method accepts a reference to an array of wxPoint objects.
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.
void EndDoc()
Ends a document (only relevant when outputting to a printer).
void EndDrawing()
Allows optimization of drawing code under MS Windows. Enclose drawing primitives between BeginDrawing and EndDrawing calls.
void EndPage()
Ends a document page (only relevant when outputting to a printer).
bool 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:
Returns false if the operation failed.
Note: The present implementation for non-Windows platforms may fail to find colour borders if the pixels do not match the colour exactly. However the function will still return true.
const wxBrush& GetBackground() const
Gets the brush used for painting the background (see wxDC::SetBackground).
int GetBackgroundMode() const
Returns the current background mode: wxSOLID or wxTRANSPARENT.
See also
const wxBrush& GetBrush() const
Gets the current brush (see wxDC::SetBrush).
wxCoord GetCharHeight()
Gets the character height of the currently set font.
wxCoord GetCharWidth()
Gets the average character width of the currently set font.
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.
wxPerl note: This method takes no arguments and returns a four element list ( x, y, width, height )
const wxFont& GetFont() const
Gets the current font (see wxDC::SetFont).
int GetLogicalFunction()
Gets the current logical function (see wxDC::SetLogicalFunction).
int GetMapMode()
Gets the mapping mode for the device context (see wxDC::SetMapMode).
bool GetOptimization()
Returns true if device context optimization is on. See wxDC::SetOptimization for details.
bool GetPartialTextExtents(const wxString& text, wxArrayInt& widths) const
Fills the widths array with the widths from the begining of text to the coresponding character of text. The generic version simply builds a running total of the widths of each character using GetTextExtent, however if the various platforms have a native API function that is faster or more accurate than the generic implementaiton then it should be used instead.
wxPython note: This method only takes the text parameter and returns a Python list of integers.
const wxPen& GetPen() const
Gets the current pen (see wxDC::SetPen).
bool GetPixel(wxCoord x, wxCoord y, wxColour *colour)
Sets colour to the colour at the specified location. Not available for wxPostScriptDC or wxMetafileDC.
wxPython note: For wxPython the wxColour value is returned and is not required as a parameter.
wxPerl note: This method only takes the parameters x and y and returns a Wx::Colour value
wxSize GetPPI() const
Returns the resolution of the device in pixels per inch.
void GetSize(wxCoord *width, wxCoord *height) const
wxSize GetSize() const
This gets the horizontal and vertical resolution in device units. It can be used to scale graphics to fit the page. 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) |
wxPerl note: In place of a single overloaded method, wxPerl uses:
| GetSize() | Returns a Wx::Size |
| GetSizeWH() | Returns a 2-element list ( width, height ) |
void GetSizeMM(wxCoord *width, wxCoord *height) const
wxSize GetSizeMM() const
Returns the horizontal and vertical resolution in millimetres.
const wxColour& GetTextBackground() const
Gets the current text background colour (see wxDC::SetTextBackground).
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) |
wxPerl note: In wxPerl this method is implemented as GetTextExtent( string, font = undef ) returning a four element array ( width, height, descent, externalLeading )
const wxColour& GetTextForeground() const
Gets the current text foreground colour (see wxDC::SetTextForeground).
void GetUserScale(double *x, double *y)
Gets the current user scale factor (set by SetUserScale).
wxPerl note: In wxPerl this method takes no arguments and return a two element array ( x, y )
wxCoord LogicalToDeviceX(wxCoord x)
Converts logical X coordinate to device coordinate, using the current mapping mode.
wxCoord LogicalToDeviceXRel(wxCoord x)
Converts logical X coordinate to relative device coordinate, using the current mapping mode but ignoring the x axis orientation. Use this for converting a width, for example.
wxCoord LogicalToDeviceY(wxCoord y)
Converts logical Y coordinate to device coordinate, using the current mapping mode.
wxCoord LogicalToDeviceYRel(wxCoord y)
Converts logical Y coordinate to relative device coordinate, using the current mapping mode but ignoring the y axis orientation. Use this for converting a height, for example.
wxCoord MaxX()
Gets the maximum horizontal extent used in drawing commands so far.
wxCoord MaxY()
Gets the maximum vertical extent used in drawing commands so far.
wxCoord MinX()
Gets the minimum horizontal extent used in drawing commands so far.
wxCoord MinY()
Gets the minimum vertical extent used in drawing commands so far.
bool Ok()
Returns true if the DC is ok to use.
void ResetBoundingBox()
Resets the bounding box: after a call to this function, the bounding box doesn't contain anything.
See also
void SetAxisOrientation(bool xLeftRight, bool yBottomUp)
Sets the x and y axis orientation (i.e., the direction from lowest to highest values on the axis). The default orientation is the natural orientation, e.g. x axis from left to right and y axis from bottom up.
Parameters
xLeftRight
yBottomUp
void SetBackground(const wxBrush& brush)
Sets the current background brush for the DC.
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.
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.
void SetClippingRegion(wxCoord x, wxCoord y, wxCoord width, wxCoord height)
void SetClippingRegion(const wxPoint& pt, const wxSize& sz)
void SetClippingRegion(const wxRect& rect)
void SetClippingRegion(const wxRegion& region)
Sets the clipping region for this device context to the intersection of the given region described by the parameters of this method and the previously set clipping region. You should call DestroyClippingRegion if you want to set the clipping region exactly to the region specified.
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
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.
void SetFont(const wxFont& font)
Sets the current font for the DC. It must be a valid font, in particular you should not pass wxNullFont to this method.
See also wxFont.
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 dstThe 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.
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, scalable TrueType fonts are always used; in X, results depend on availability of fonts, but usually a reasonable match is found.
The coordinate origin is always at the top left of the screen/printer.
Drawing to a Windows printer device context 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. |
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-wxWidgets 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 wxWidgets 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.
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.
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.
void SetTextBackground(const wxColour& colour)
Sets the current text background colour for the DC.
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.
void SetUserScale(double xScale, double yScale)
Sets the user scaling factor, useful for applications which require 'zooming'.
bool StartDoc(const wxString& message)
Starts a document (only relevant when outputting to a printer). Message is a message to show whilst printing.
bool StartPage()
Starts a document page (only relevant when outputting to a printer).