GDI Drawing in MFC (4)

3. Create a drawing tool and select INTO DC

With the canvas, we have to have a paintbrush brush to draw. With GDI objects such as Hpen, Hbrush, and so on in Windows, MFC encapsulates GDI objects nicely, providing classes that encapsulate GDI objects, such as CPen, CBrush, CFont, CBitmap, and CPalette, These classes are derived classes of the GDI object class CGdiObject.

Usually first create a brush (brush), and then call the CDC::SelectObject function to select the brush (brush) into the device environment the most current drawing tool, drawing finished to restore the device environment before the brush (brush) object, and finally call CGdiObject::D The Eleteobject function deletes a brush (brush) object.

It is important to note that CGdiObject: the:D eleteobject function completely removes the underlying GDI objects (base classes for CPen and CBrush classes). In MFC, when an object is destroyed, the destructor of the object is called automatically to delete the object, and it is generally not necessary to call CGdiObject::D eleteobject To delete the GDI object, because if the device environment is still using a GDI object, the application crashes or an incomprehensible run error occurs.

(1) Creating brushes

BOOL CPen::CreatePen(int npenstyle, int nwidth, COLORREF cfcolor);

Npenstyle Specifies the style of the brush. See the Npenstyle parameter in the CPen constructor for a list of possible values.

nwidth Specifies the width of the brush. If this value is 0, the width in device units is always one pixel, regardless of the mapping mode.

The crcolor contains an RGB color for the brush, which is the COLORREF structure.

In addition, the Cdc::selectstockobject function can be used to invoke the CGdiObject object corresponding to the system's pre-defined inventory pen.

Poldpen = (cpen*) pdc->selectstockobject (Black_pen);

(2) Creating a paint brush

BOOL CBrush::createsolidbrush (colorref crcolor);

BOOL CBrush::createhatchbrush(int nIndex, COLORREF crcolor);

Parameter: nIndex Specifies the shaded line style of the brush. The following values are desirable:

Hs_horizontal * * = = =

Hs_vertical/* | | | | | * *

Hs_fdiagonal/ * \\\\\ * /

Hs_bdiagonal/ */////* /

Hs_cross/ * +++++ * /

Hs_diagcross/ * xxxxx * /

Return value: Returns a value other than 0 if the call succeeds, otherwise 0.

In addition, the Cdc::selectstockobject function can be used to invoke the CGdiObject object corresponding to the system's pre-defined inventory brush.

Poldbrush = (cbrush*) pdc->selectstockobject (Black_brush);

(3) Select the brush (brush) into the device environment.

The following is the module for GDI drawing in the default mapping mode in MFC:

Get the device environment first PDC

CPen *poldpen,newpen;

CBrush *poldbrush,newbrush1,newbrush2;

// Create A solid white line brush with a width of pixel

Newpen.createpen (Ps_solid,1,rgb (0,0,0));

// Create a red solid line paint brush

Newbrush1.createsolidbrush (RGB (255,0,0));

// creates a shadow brush of the downward (right-to-left) shadow of a solid red line

Newbrush2.createhatchbrush (Hs_bdiagonal,rgb (255,0,0));

// Selecting Newpen brushes and NewBrush1 brush objects into the device environment

Poldpen = Pdc->selectobject (&newpen);

Poldbrush = Pdc->selectobject (&NEWBRUSH1);

// calling a DC drawing function drawing

// ...

// finish drawing, restore the original brush, paint brush

Pdc->selectobject (Poldpen);

Pdc->selectobject (Poldbrush);

// Delete a created brush, paint brush

Newpen.deleteobject ();

Newbrush1.deleteobject ();

Newbrush2.deleteobject ();

(4) When the text is drawn, you can generally call the Cdc::setbkcolor function to set the background color, call the Cdc::settextcolor function to set the text color, call the Cdc::settextalign function to set the text alignment tag.

4. Call the DC drawing function drawing

GDI provides member functions for drawing basic graphics, which are encapsulated in the CDC class in MFC.

Note: The coordinates used by the drawing function are logical coordinates.

Common CDC drawing functions
Function	Function
Line output function
GetCurrentPosition	Gets the current position of the pen, expressed in logical coordinates
MoveTo	Move Current position
LineTo	Draw a line from the current position to a point, but do not include that point
Arc	Draw an elliptical arc
ArcTo	Draw an elliptical arc. In addition to updating the current location, this function is similar to ARC
Polypolyline	Draw multiple groups of connected segments. This function does not use or update the current position
PolylineTo	Draw one or more lines and move the current position to the end of the last line
Polybezier	Draw one or more Bezier splines. Do not use or update the current location
PolyBezierTo	Draw one or more Bezier splines and move the current position to the end of the last Bezier spline
Ellipse and Polygon functions
Chord	Draws an elliptical arc (an ellipse and a closed shape that intersects a segment)
DrawFocusRect	Draws the style rectangle used to represent the focus
Ellipse	Draw Ellipse
Pie	Draw a pie chart
Polygon	Draws a polygon, containing one or more points (vertices) connected by a segment
Polypolygon	Create two or more polygons that use the current polygon fill mode, and polygons can be separated or superimposed on each other
Polyline	Draws a polygon that contains a set of segments that connect to a specified point
Rectangle	Draws a rectangle with the current pen, fills it with the current paint brush
RoundRect	Draws a rounded rectangle with the current pen and fills it with the current paint brush
Bitmap functions
BitBlt	Copy a bitmap from a specified device context
StretchBlt	Moves the bitmap from the source rectangle and device to the target rectangle, stretching or compressing the bitmap if necessary to fit the dimension of the destination rectangle
GetPixel	Gets the RGB color value for the specified point pixel
SetPixel	Sets the approximate value of the specified point pixel to the nearest specified color
Text functions
TextOut	Writes a string at the specified position with the currently selected font
ExtTextOut	Writes a string in the rectangular area with the currently selected font
TabbedTextOut	Writes a string at the specified position, and the tab extension specifies the value in the tab stop position array
DrawText	Draws formatted text within the specified rectangle
For-------------------details, refer to MSDN, MFC class Library-----------------

--------------------to Be Continued------------------

GDI Drawing in MFC (4)