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wxDC: wxObject

Overview

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 canvas has a device context 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.

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


wxDC::wxDC

void wxDC(void)

Constructor.


wxDC::~wxDC

void ~wxDC(void)

Destructor.


wxDC::BeginDrawing

void BeginDrawing(void)

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

Drawing to a wxDialogBox 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(float xdest, float ydest, float width, float height,
wxDC *source, float xsrc, float ysrc, int logical_func, Bool transparent = 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 (see wxDC::SetLogicalFunction). See wxMemoryDC for typical usage.

If transparent is TRUE and source is a wxMemoryDC with a transparent bitmap selected into it, the function will draw the source transparently. At present, the only way to create a transparent bitmap is to load a transparent XPM.

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


wxDC::Clear

void Clear(void)

Clears the device context using the current background brush.


wxDC::CrossHair

void CrossHair(float x, float y)

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


wxDC::DestroyClippingRegion

void DestroyClippingRegion(void)

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


wxDC::DeviceToLogicalX

float DeviceToLogicalX(int x)

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


wxDC::DeviceToLogicalXRel

float DeviceToLogicalXRel(int 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

float DeviceToLogicalY(int y)

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


wxDC::DeviceToLogicalYRel

float DeviceToLogicalYRel(int 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(float x1, float y1, float x2, float y2, floatxc, floatyc)

Draws an arc, 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.


wxDC::DrawEllipse

void DrawEllipse(float x, float y, float width, float 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(float x, float y, float width, float height, floatstart, floatend)

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. This function is currently only available for X canvas and PostScript device contexts.

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(wxIcon *icon, float x, float 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 canvas.


wxDC::DrawLine

void DrawLine(float x1, float y1, float x2, float 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[], float xoffset = 0, float yoffset = 0)

void DrawLines(wxList *points, float xoffset = 0, float 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.


wxDC::DrawPolygon

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

void DrawPolygon(wxList *points, float xoffset = 0, float 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.


wxDC::DrawPoint

void DrawPoint(float x, float y)

Draws a point using the current pen.


wxDC::DrawRectangle

void DrawRectangle(float x, float y, float width, float 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::DrawRoundedRectangle

void DrawRoundedRectangle(float x, float y, float width, float height, float 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(float x1, float y1, float x2, float y2, float x3, float y3)

Draws a three-point spline using the current pen.


wxDC::DrawText

void DrawText(char *text, float x, float 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.


wxDC::EndDoc

void EndDoc(void)

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


wxDC::EndDrawing

void EndDrawing(void)

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


wxDC::EndPage

void EndPage(void)

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


wxDC::FloodFill

void FloodFill(float x, float y, wxColour *colour, int style=wxFLOOD_SURFACE)

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

Note: this function is available in MS Windows only.


wxDC::GetBackground

wxBrush * GetBackground(void)

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


wxDC::GetBrush

wxBrush * GetBrush(void)

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


wxDC::GetCharHeight

float GetCharHeight(void)

Gets the character height of the currently set font.


wxDC::GetCharWidth

float GetCharWidth(void)

Gets the average character width of the currently set font.


wxCanvas::GetClippingBox

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

Gets the rectangle surrounding the current clipping region.


wxDC::GetFont

wxFont * GetFont(void)

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


wxDC::GetLogicalFunction

int GetLogicalFunction(void)

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


wxDC::GetMapMode

int GetMapMode(void)

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


wxDC::GetOptimization

Bool GetOptimization(void)

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


wxDC::GetPen

wxPen * GetPen(void)

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


wxDC::GetPixel

Bool GetPixel(float x, float 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.


wxDC::GetSize

void GetSize(float *width, float *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:

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

wxDC::GetTextBackground

wxColour& GetTextBackground(void)

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


wxDC::GetTextExtent

void GetTextExtent(char *string, float *w, float *h,
float *descent = NULL, float *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.


wxDC::GetTextForeground

wxColour& GetTextForeground(void)

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


wxDC::IntDrawLine

void IntDrawLine(int x1, int y1, int x2, int y2)

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


wxDC::IntDrawLines

void IntDrawLines(int n, wxIntPoint points[], int xoffset = 0, int yoffset = 0)

Draw lines using an array of points of size n. The current pen is used for drawing the lines. The programmer is responsible for deleting the list of points.


wxDC::LogicalToDeviceX

int LogicalToDeviceX(float x)

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


wxDC::LogicalToDeviceXRel

int LogicalToDeviceXRel(float x)

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


wxDC::LogicalToDeviceY

int LogicalToDeviceY(float y)

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


wxDC::LogicalToDeviceYRel

int LogicalToDeviceYRel(float y)

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


wxDC::MaxX

float MaxX(void)

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


wxDC::MaxY

float MaxY(void)

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


wxDC::MinX

float MinX(void)

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


wxDC::MinY

float MinY(void)

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


wxDC::Ok

Bool Ok(void)

Returns TRUE if the DC is ok to use.


wxDC::SetDeviceOrigin

void SetDeviceOrigin(float x, float 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(wxBrush *brush)

Sets the current background brush for the DC. Do not delete the brush; it will be deleted automatically when the application terminates.


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(float x, float y, float width, float height)

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

See also wxDC::DestroyClippingRegion.


wxDC::SetColourMap

void SetColourMap(wxColourMap *colourMap)

If this is a canvas DC or memory DC, assigns the given colourmap to the window or bitmap associated with the DC. If the argument is NULL, the current colourmap is selected out of the device context, and the original colourmap restored, allowing the current colourmap to be destroyed safely.

See wxColourMap for further details.


wxDC::SetBrush

void SetBrush(wxBrush *brush)

Sets the current brush for the DC. The brush is not copied, so you should not delete the brush unless the DC pen has been set to another brush, or to NULL. Note that all pens and brushes are automatically deleted when the program is exited.

If the argument is NULL, 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.


wxDC::SetFont

void SetFont(wxFont *font)

Sets the current font for the DC. The font is not copied, so you should not delete the font unless the DC pen has been set to another font, or to NULL.

If the argument is NULL, 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 canvas. 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. wxXOR 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:

MM_TWIPS Each logical unit is 1/20 of a point, or 1/1440 of an inch.
MM_POINTS Each logical unit is a point, or 1/72 of an inch.
MM_METRIC Each logical unit is 1 mm.
MM_LOMETRIC Each logical unit is 1/10 of a mm.
MM_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(wxPen *pen)

Sets the current pen for the DC. The pen is not copied, so you should not delete the pen unless the DC pen has been set to another pen, or to NULL. Note that all pens and brushes are automatically deleted when the program is exited.

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


wxDC::SetTextBackground

void SetTextBackground(wxColour *colour)

Sets the current text background colour for the DC.


wxDC::SetTextForeground

void SetTextForeground(wxColour *colour)

Sets the current text foreground colour for the DC.


wxDC::SetUserScale

void SetUserScale(float x_scale, floaty_scale)

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


wxDC::StartDoc

Bool StartDoc(char *message)

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


wxDC::StartPage

Bool StartPage(void)

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