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Drawing Arrows

, 30 Nov 2002
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How to draw arrows (with arrowheads) to an arbitrary DC.

Sample Image - Arrows.jpg

Excuse

Basically, there was a request for some code to draw arrows and I had never seen any. Plus, I'm not really in the mood to hang drapes or vacuum.

Using the code

This is a simple API for drawing lines with arrowheads. It looks like this:

// ARROWSTRUCT
//
// Defines the attributes of an arrow.
typedef struct tARROWSTRUCT {
    int nWidth;     // width (in pixels) of the full base of the arrowhead
    float fTheta;   // angle (in radians) at the arrow tip between the two
                    //  sides of the arrowhead
    bool bFill;     // flag indicating whether or not the arrowhead should be
                    //  filled
} ARROWSTRUCT;

// ArrowTo()
//
// Draws an arrow, using the current pen and brush, from the current position
//  to the passed point using the attributes defined in the ARROWSTRUCT.
void ArrowTo(HDC hDC, int x, int y, ARROWSTRUCT *pArrow);
void ArrowTo(HDC hDC, const POINT *lpTo, ARROWSTRUCT *pArrow);

Simply fill an ARROWSTRUCT with the desired attributes, make sure the current DC position is correct (MoveTo(), etc.), and call one of the two ArrowTo() functions. The size parameters (nWidth and fTheta) are defined as follows:

Technique

This goes back to high-school algebra and trigonometry. The ArrowTo() function first builds a vector of the full line. Then it calculates the points for the sides of the arrowhead based on the nWidth and fTheta attributes you pass. Badda-boom-badda-bing, you got your arrowhead.

Here's some pseudo-pseudocode:

lineVector = toPoint - fromPoint
lineLength = length of lineVector

// calculate point at base of arrowhead
tPointOnLine = nWidth / (2 * (tanf(fTheta) / 2) * lineLength);
pointOnLine = toPoint + -tPointOnLine * lineVector

// calculate left and right points of arrowhead
normalVector = (-lineVector.y, lineVector.x)
tNormal = nWidth / (2 * lineLength)
leftPoint = pointOnLine + tNormal * normalVector
rightPoint = pointOnLine + -tNormal * normalVector

History

  • December 1 2002 - Created.

License

This article has no explicit license attached to it but may contain usage terms in the article text or the download files themselves. If in doubt please contact the author via the discussion board below.

A list of licenses authors might use can be found here

About the Author

Jamie Hale
Web Developer
Canada Canada
No Biography provided

Comments and Discussions

 
QuestionUrgent PinmemberMember 104154789-May-14 5:34 
GeneralMy vote of 5 Pinmembermanoj kumar choubey22-Feb-12 0:02 
SuggestionSome suggestions Pinmemberherohuyongtao8-Oct-11 20:52 
GeneralCorrecting the math for better arrow heads Pinmemberbstrack17-Feb-10 8:09 
Generalquestion PinmemberLuo Rui4-Dec-06 2:24 
GeneralFreaks out in release mode Pinmembermark-w24-Sep-06 8:30 
GeneralRe: Freaks out in release mode Pinmembermark-w24-Sep-06 8:55 
GeneralRe: Freaks out in release mode PinmemberJamie Hale25-Sep-06 4:23 
GeneralRe: Freaks out in release mode Pinmembermark-w30-Sep-06 19:30 
AnswerRe: Freaks out in release mode PinmemberClemensR18-Sep-07 5:10 
GeneralRe: Freaks out in release mode Pinmemberkkokkal14-Jan-08 20:23 
GeneralJust another approach Pinmemberprcarp10-May-06 3:27 
GeneralRe: Just another approach Pinmemberrsantos0123-Nov-06 4:54 
GeneralI am looking for a simple MFC Control with Draw Area Pinmemberp2002ad25-May-05 6:14 
GeneralLength of arrow PinmemberHemant kulkarni2-Dec-02 20:11 
GeneralRe: Length of arrow PinmemberPhilippe Lhoste2-Dec-02 23:07 
GeneralRe: Length of arrow PinmemberPhilippe Lhoste3-Dec-02 1:53 
GeneralRe: Length of arrow PinmemberJamie Hale3-Dec-02 4:50 
GeneralRe: Length of arrow PinmemberJamie Hale3-Dec-02 4:51 
GeneralHeight of the arrowhead PinmemberMetalRob14-Nov-10 23:48 
GeneralRe: Height of the arrowhead PinmemberJamie Hale15-Nov-10 0:00 
GeneralRe: Height of the arrowhead PinmemberMetalRob15-Nov-10 0:17 
GeneralRe: Height of the arrowhead PinmemberMetalRob15-Nov-10 0:18 
GeneralAnother way: matrix transformation (don't be scared it's easy!) :) PinmemberDamir Valiulin2-Dec-02 13:05 
GeneralRe: Another way: matrix transformation (don't be scared it's easy!) :) PinmemberJamie Hale3-Dec-02 4:48 
Generalnice, but GDI+ can do it better Pinmemberafisser2-Dec-02 2:15 
GeneralRe: nice, but GDI+ can do it better PinmemberJamie Hale2-Dec-02 5:27 
GeneralRe: nice, but GDI+ can do it better PinmemberPhilippe Lhoste2-Dec-02 23:01 
GeneralFirst non-joke thread! PineditorNishant S1-Dec-02 14:11 
GeneralRe: First non-joke thread! PinmemberShog91-Dec-02 15:07 
GeneralRe: First non-joke thread! PinmemberJamie Hale1-Dec-02 17:02 
QuestionWhere are the other 7? PineditorNishant S1-Dec-02 14:09 

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