How To Draw TrueType Glyph Outlines

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The Win32 APIGetGlyphOutlinefunction can return native glyph outline data from a TrueType font. To draw a TrueType glyph outline, the data must be converted from its native B-Spline definition to a sequence of Bezier line definitions. Then thePolyBezierWin32 API function can be used to draw the outline.

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TheGetGlyphOutlinefunction in the Win32 Application Programming Interface(API) can retrieve a TrueType outline. The GGO_NATIVE format option fills a buffer with Quadratic B-Spline curves for a TrueType outline. ???? ???? ????? ???? ??? ????? ???? glyph ?? ????? ???? ?? ??? quadratic B-Splines ????? ???? ???? ?? ??? ???? ?? B Spline ????? ?????? ?? ??????????? ?? ???? ??? ?? ????? ?? ????????? ?????? ?? ????? ?? ???PolyBezierWin32 API ?? ????????

Quadratic B Spline ?????? ?? ???????? ?? ??? ??????? ?? ?????? ?? ?? ?? ???? ???? ??? ?? ?? ?? ????????? parametric ?????? ?? ?? ???? ???? ???? Quadratic ???? ?? ?? ????? ???? parametric ???? ??? There is no function in the API to draw a Quadratic Spline directly but if the Quadratic is converted to a Cubic it can be drawn with the Win32 API function for drawing a Bezier curve; calledPolyBezier.

Quadratic B-Spline curves in particular and parametric curves in general are a well-researched topic of graphics in computer science. They can also be quite complex. Algorithms have been published in various texts that can be used to implement a function to draw a Quadratic Spline, but describing such an algorithm is beyond the scope of this article.

ThePolyBezierfunction can draw a Quadratic Spline because a Bezier curve is a cubic or third order parametric curve. Since a Quadratic Spline is a second order equation, it can be expressed in terms of the higher order cubic equation. Although an equation for expressing a quadratic as a cubic is given in the sample code, its derivation is not discussed in this article.

The sample code in this article is a demonstration of how to parse a GGO_NATIVE glyph buffer returned by theGetGlyphOutline?????? ?? ??? ???? ???.. The buffer returned by the GGO_NATIVE format flag conforms to theTTPOLYGONHEADER?????? ??? TheTTPOLYGONHEADERstructure and the data that immediately follows it constitute one contour of a TrueType glyph. A contour is one complete path of curves that is implicitly closed if it is not explicitly returned that way.

Please see the Platform SDK for documentation on theTTPOLYGONHEADER, ??TTPOLYCURVE?????????

A glyph contour consists of multiple curve segments represented byTTPOLYCURVE????????? In a contour, theTTPOLYGONHEADERis followed by one or moreTTPOLYCURVEstructures and coordinate point data. ThepfxStartmember gives the starting coordinate point of the contour. The count of curve records that follow theTTPOLYGONHEADERis given by thecb????? ??? ??????? ????? glyph ?? ??? ????? ?? ??????? ??? ??? glyph ?? ?????, ???? ?? ???? ???? ?? ???? ?? ????? ???? ???? ???

????????TTPOLYCURVE???? ?????? (?? ???? ???) Quadratic B-Spline ???????? ????? ?? ?????? Polyline ????? ?? ????? ??? ???? ??? ??????? ?? ?????? ?????? ?? ?? ??TTPOLYCURVEcpfx????? ??? ???? ?????? spline ?? polyline ?? ?????? ?? ?? ??wType????? ??? ???? coordinate ??????? ?? ????? ?????? ?? ????? ???? ?? ??????? ????? ?????? ?? ?? ??apfx????? ???

??? glyph ??? ?? ?? ???? contour ?? ???? ??, ??????? ???? ?? ?? ?? ???? ???? ??? ???TTPOLYGONHEADER???????? ?? ???? ??? ?????? contours ????? ??? ???? ??? ????? ?? ????? packed ???? ???? contour ?? ??? ??????? ?? ???? ?? ??TTPOLYGONHEADER?? ????? ????? ?? ????? ???? ??????? ?? ??? ???? ?????

?? ????? ??? ??????? ???? ??? ?? ???????? contour ??????? ?? ???? ????? ?? ??? GGO_NATIVE ???? ?? ????? ???? ?? ?????? ?? ???? ???? glyph ?? ????? ???? ?????? ???? ??? ??????? ???? ??? ?? ???? ?? ????? ?? ???? ?? ?? ??PolyBezier. The code that parses the buffer is in theDrawT2Outline?????? ?? ??? ???? ???..

The first step to create a list of Bezier lines is to determine the size of the buffer for the list. Four points define Bezier lines. ThePolyBezierfunction interprets an array of points as being one continuous line of Bezier segments where the start of the next line is coincident with the endpoint of the previous line. Thus, only three points are needed to describe an additional Bezier line segment.

The GGO_NATIVE buffer may contain either a polyline curve or a Quadratic B-Spline curve. ?? ??? ???? ??? ???? ????????? ???? ???? ??? ????? B-Spline ???? ????????? ????? ???????? ?????? ?? PolyBezier ?? ????? ?? ?? ??????? ???? ?????? ???? ?? ??? ??, ??????? worst ??? ???????? ???? ?? ???? ?? ???? ??? ?? composed ???? ??? ?? contour ?????? ????????? ?? ??????? ???? ???

??? ???? ?? ??? ???????? ???? ?? ?????? ???? ?? ??? ??? ??? ??? B Spline ???? ???? ?????? ???????? ???? ?? ????? ??? ?? ????? ?????? ??? ?? "B" ????????? ???? ?? ?? ??? ???? ????? ???? ?? implicitly ????????? ???????? ????? ????? ??? ?? ????? ????? ?? ???? "B" ????? midpoint ??? ?????? ?? ?? ??? ???????? ???? ??? ?? ??? ???????? ???? ??? ????? ??????? ??????? ???? ?? ??? ???????? ??????? ?? ????

?? ??? ????? ?? ??????? ??? ???? ?? ??? ????POINTFX????????, ????? ?? ????? ???? ?? ?????? ???????? ???? ???? ?? ???? ??????? ?? ?????? ????????? ?? ???? ???? ???? ????? ???? ???? contours ?? ?????? ??? ?????? overhead ?? ??????? ???????? ?????? ???? ?? ???? ??? ??????? ???? ?? ??? ???? ?? ???? ?????? ???? ?????? ?? ???? ?? ???? ?????? multiplied ??????? ?? ?????? ?? ?? ?? ???????structure ?? ??? ?????? multiplied. ??? ???????? ???????? ???? ??? ?? ??? ??????? ??? ?????? ???? ??? quadratic spline ??? ?? ??? ?????? ???????? ??????? ?? ?????? ???

??????? ???? ?? ?????? ???? ??? ?? ?? ??? ??? ?????? ??? ???? ?? ???? ?? ????? ??????? ?? ??? ??TTPOLYGONHEADER. ??? ?? ??? ??????????? ?? ????? ??? ?? contour ??????? ???? ?? ?? ??? ????? ??? ????? ????? ??? ?????? ???????? ???? ?????? ???

???? polyline ???? (TT_PRIM_LINE), ?? ????? ??? polyline ?? ???????? ???? ??? ??? ?????? ???? ?? ?? ??? ????????? ?? ???? ??? ????? ????AppendPolyLineToBezier?????? ?? ??? ???? ???.. ??? ???? ??? ?? Quadratic B Spline (TT_PRIM_QSPLINE), ??AppendQuadBSplineToBezier?????? ??? ?????? ???? ?? ?? Quadratic B-Spline appends ??? ?? ?????? ?? ?? ??? ???????? ??? ?? ???? ?? ???? ???? ???????? ???????? ??????? ??? ????? ???? ?? ??? ????? ???? ??? ??? ??? ?????? ?? spline ?? ??? ?????? ???? ?? ??? ??? ??????? ?? ????????? ?? ???? ??? ????? ???? ????

??????? ???? ?? ???? ??? ?? ???? ???? ?????? ????? ??? ??????? ?? ????? vectors ????? ????? ???? ??? ?? ?????? ??? ???? ?? ?? ??? ??MakeBezierFromLine?????? ?? ??? ???? ???..

??? quadratic spline ?? ?? cubic ??????? spline ??? ?????? ???? ?? ??? quadratic ???????? ??????? ?? ????? ??? cubic ???????? ????? expressing ?????? ???????? ??????? ?? ?????? ?? ??? ?????? ??? ????? ??MakeBezierFromQBSpline?????? ?? ??? ???? ???..

Contour ?????, ???? ?? ???? ??? ????????? ???? ?? ?? ??? ?????? ?? ??? ??CloseContour?????? ?? ??? ???? ???.. ?????? ?? ??? ???? ???? ?? ???? ??? ??????? ?? ????????? ?? ???? ?? ??? ????? coincident ???? ???? ???PolyBezier?????? ?? ??? ???? ???? ???

Contour ???? ?? ??, ?? ??? ???? contourTTPOLYGONHEADER??????? contour ??? ???????? ?? ??? ?? ??? lpHeader ???? advancing ?? ????? ??? ??? ?? ?????? ???? ???? ??? ??? ???? ?? ??? ?? ???, ??? ?? ??????? ??? contours ?? exits.
/****************************************************************************
 *  FUNCTION   : IntFromFixed
 *  RETURNS    : int value approximating the FIXED value.
 ****************************************************************************/ 
int PASCAL NEAR IntFromFixed(FIXED f)
{
    if (f.fract >= 0x8000)
    return(f.value + 1);
    else
    return(f.value);
}

/****************************************************************************
 *  FUNCTION   : fxDiv2
 *  RETURNS    : (val1 + val2)/2 for FIXED values
 ****************************************************************************/ 
FIXED PASCAL NEAR fxDiv2(FIXED fxVal1, FIXED fxVal2)
{
    long l;

    l = (*((long far *)&(fxVal1)) + *((long far *)&(fxVal2)))/2;
    return(*(FIXED *)&l);
}

/****************************************************************************
 *  FUNCTION   : MakeBezierFromLine
 *
 *  PURPOSE    : Converts a line define by two points to a four point Bezier
 *               spline representation of the line in pPts.
 *
 *
 *  RETURNS    : number of Bezier points placed into the pPts POINT array.
 ****************************************************************************/ 
UINT MakeBezierFromLine( POINT *pPts, POINT startpt, POINT endpt )
{
    UINT cTotal = 0;

    // starting point of Bezier
    pPts[cTotal] = startpt;
    cTotal++;

    // 1rst Control, pt == endpoint makes Bezier a line
    pPts[cTotal].x = endpt.x;
    pPts[cTotal].y = endpt.y;
    cTotal++;

    // 2nd Control, pt == startpoint makes Bezier a line
    pPts[cTotal].x = startpt.x;
    pPts[cTotal].y = startpt.y;
    cTotal++;

    // ending point of Bezier
    pPts[cTotal] = endpt;
    cTotal++;
    
    return cTotal;
}

/****************************************************************************
 *  FUNCTION   : MakeBezierFromQBSpline
 *
 *  PURPOSE    : Converts a quadratic spline in pSline to a four point Bezier
 *               spline in pPts.
 *
 *
 *  RETURNS    : number of Bezier points placed into the pPts POINT array.
 ****************************************************************************/ 
UINT MakeBezierFromQBSpline( POINT *pPts, POINTFX *pSpline )
{
    POINT   P0,         // Quadratic on curve start point
            P1,         // Quadratic control point
            P2;         // Quadratic on curve end point
    UINT    cTotal = 0;

    // Convert the Quadratic points to integer
    P0.x = IntFromFixed( pSpline[0].x );
    P0.y = IntFromFixed( pSpline[0].y );
    P1.x = IntFromFixed( pSpline[1].x );
    P1.y = IntFromFixed( pSpline[1].y );
    P2.x = IntFromFixed( pSpline[2].x );
    P2.y = IntFromFixed( pSpline[2].y );

    // conversion of a quadratic to a cubic

    // Cubic P0 is the on curve start point
    pPts[cTotal] = P0;
    cTotal++;
    
    // Cubic P1 in terms of Quadratic P0 and P1
    pPts[cTotal].x = P0.x + 2*(P1.x - P0.x)/3;
    pPts[cTotal].y = P0.y + 2*(P1.y - P0.y)/3;
    cTotal++;

    // Cubic P2 in terms of Qudartic P1 and P2
    pPts[cTotal].x = P1.x + 1*(P2.x - P1.x)/3;
    pPts[cTotal].y = P1.y + 1*(P2.y - P1.y)/3;
    cTotal++;

    // Cubic P3 is the on curve end point
    pPts[cTotal] = P2;
    cTotal++;

    return cTotal;
}


/****************************************************************************
 *  FUNCTION   : AppendPolyLineToBezier
 *
 *  PURPOSE    : Converts line segments into their Bezier point 
 *               representation and appends them to a list of Bezier points. 
 *
 *               WARNING - The array must have at least one valid
 *               start point prior to the address of the element passed.
 *
 *  RETURNS    : number of Bezier points added to the POINT array.
 ****************************************************************************/ 
UINT AppendPolyLineToBezier( LPPOINT pt, POINTFX start, LPTTPOLYCURVE lpCurve )
{
    int     i;
    UINT    cTotal = 0;
    POINT   endpt;
    POINT   startpt;
    POINT   bezier[4];

    endpt.x = IntFromFixed(start.x);
    endpt.y = IntFromFixed(start.y);

    for (i = 0; i < lpCurve->cpfx; i++)
    {
        // define the line segment
        startpt = endpt;
        endpt.x = IntFromFixed(lpCurve->apfx[i].x);
        endpt.y = IntFromFixed(lpCurve->apfx[i].y);

        // convert a line to a bezier representation
        MakeBezierFromLine( bezier, startpt, endpt );

        // append the Bezier to the existing ones
                                    // Point 0 is Point 3 of previous.
        pt[cTotal++] = bezier[1];   // Point 1
        pt[cTotal++] = bezier[2];   // Point 2
        pt[cTotal++] = bezier[3];   // Point 3

    }

    return cTotal;
}


/****************************************************************************
 *  FUNCTION   : AppendQuadBSplineToBezier
 *
 *  PURPOSE    : Converts Quadratic spline segments into their Bezier point 
 *               representation and appends them to a list of Bezier points. 
 *
 *               WARNING - The array must have at least one valid
 *               start point prior to the address of the element passed.
 *
 *  RETURNS    : number of Bezier points added to the POINT array.
 ****************************************************************************/ 
UINT AppendQuadBSplineToBezier( LPPOINT pt, POINTFX start, LPTTPOLYCURVE lpCurve )
{
    WORD                i;
    UINT                cTotal = 0;
    POINTFX             spline[3];  // a Quadratic is defined by 3 points
    POINT               bezier[4];  // a Cubic by 4

    // The initial A point is on the curve.
    spline[0] = start;

    for (i = 0; i < lpCurve->cpfx;)
    {
        // The B point.
        spline[1] = lpCurve->apfx[i++];

        // Calculate the C point.
        if (i == (lpCurve->cpfx - 1))
        {
            // The last C point is described explicitly
            // i.e. it is on the curve.
            spline[2] = lpCurve->apfx[i++];
        }     
        else
        {
            // C is midpoint between B and next B point
            // because that is the on curve point of 
            // a Quadratic B-Spline.
            spline[2].x = fxDiv2(
                lpCurve->apfx[i-1].x,
                lpCurve->apfx[i].x
                );
            spline[2].y = fxDiv2(
                lpCurve->apfx[i-1].y,
                lpCurve->apfx[i].y
                );
        }

        // convert the Q Spline to a Bezier
        MakeBezierFromQBSpline( bezier, spline );
        
        // append the Bezier to the existing ones
                                    // Point 0 is Point 3 of previous.
        pt[cTotal++] = bezier[1];   // Point 1
        pt[cTotal++] = bezier[2];   // Point 2
        pt[cTotal++] = bezier[3];   // Point 3

        // New A point for next slice of spline is the 
        // on curve C point of this B-Spline
        spline[0] = spline[2];
    }

    return cTotal;
}

/****************************************************************************
 *  FUNCTION   : CloseContour
 *
 *  PURPOSE    : Adds a bezier line to close the circuit defined in pt.
 *
 *
 *  RETURNS    : number of points aded to the pt POINT array.
 ****************************************************************************/ 
UINT CloseContour( LPPOINT pt, UINT cTotal )
{
    POINT               endpt, 
                        startpt;    // definition of a line
    POINT               bezier[4];

    // connect the first and last points by a line segment
    startpt = pt[cTotal-1];
    endpt = pt[0];

    // convert a line to a bezier representation
    MakeBezierFromLine( bezier, startpt, endpt );

    // append the Bezier to the existing ones
                                // Point 0 is Point 3 of previous.
    pt[cTotal++] = bezier[1];   // Point 1
    pt[cTotal++] = bezier[2];   // Point 2
    pt[cTotal++] = bezier[3];   // Point 3

    return 3;
}

/****************************************************************************
 *  FUNCTION   : DrawT2Outline
 *
 *  PURPOSE    : Decode the GGO_NATIVE outline, create a sequence of Beziers
 *               for each contour, draw with PolyBezier.  Color and relative 
 *               positioning provided by caller. The coordinates of hDC are
 *               assumed to have MM_TEXT orientation.
 *
 *               The outline data is not scaled. To draw a glyph unhinted
 *               the caller should create the font at its EMSquare size
 *               and retrieve the outline data. Then setup a mapping mode
 *               prior to calling this function.
 *
 *  RETURNS    : none.
 ****************************************************************************/ 
void DrawT2Outline(HDC hDC, LPTTPOLYGONHEADER lpHeader, DWORD size) 
{
    WORD                i;
    UINT                cTotal = 0; // Total points in a contour.
    LPTTPOLYGONHEADER   lpStart;    // the start of the buffer
    LPTTPOLYCURVE       lpCurve;    // the current curve of a contour
    LPPOINT             pt;         // the bezier buffer
    POINTFX             ptStart;    // The starting point of a curve
    DWORD               dwMaxPts = size/size of(POINTFX); // max possible pts.
    DWORD               dwBuffSize;

    dwBuffSize = dwMaxPts *     // Maximum possible # of contour points.
                 sizeof(POINT) * // sizeof buffer element
                 3;             // Worst case multiplier of one additional point
                                // of line expanding to three points of a bezier

   lpStart = lpHeader;
   pt = (LPPOINT)malloc( dwBuffSize );

    // Loop until we have processed the entire buffer of contours.
    // The buffer may contain one or more contours that begin with
    // a TTPOLYGONHEADER. We have them all when we the end of the buffer.
    while ((DWORD)lpHeader < (DWORD)(((LPSTR)lpStart) + size) && pt != NULL)
    {
        if (lpHeader->dwType == TT_POLYGON_TYPE)
        // Draw each coutour, currently this is the only valid
        // type of contour.
        {
            // Convert the starting point. It is an on curve point.
            // All other points are continuous from the "last" 
            // point of the contour. Thus the start point the next
            // bezier is always pt[cTotal-1] - the last point of the 
            // previous bezier. See PolyBezier.
            cTotal = 1;
            pt[0].x = IntFromFixed(lpHeader->pfxStart.x);
            pt[0].y = IntFromFixed(lpHeader->pfxStart.y);

            // Get to first curve of contour - 
            // it starts at the next byte beyond header
            lpCurve = (LPTTPOLYCURVE) (lpHeader + 1);

            // Walk this contour and process each curve( or line ) segment 
            // and add it to the Beziers
            while ((DWORD)lpCurve < (DWORD)(((LPSTR)lpHeader) + lpHeader->cb))
            {
                //**********************************************
                // Format assumption:
                //   The bytes immediately preceding a POLYCURVE
                //   structure contain a valid POINTFX.
                // 
                //   If this is first curve, this points to the 
                //      pfxStart of the POLYGONHEADER.
                //   Otherwise, this points to the last point of
                //      the previous POLYCURVE.
                // 
                //   In either case, this is representative of the
                //      previous curve's last point.
                //**********************************************

                ptStart = *(LPPOINTFX)((LPSTR)lpCurve - sizeof(POINTFX));
                if (lpCurve->wType == TT_PRIM_LINE)
                {
                    // convert the line segments to Bezier segments
                    cTotal += AppendPolyLineToBezier( &pt[cTotal], ptStart, lpCurve );
                    i = lpCurve->cpfx;
                }
                else if (lpCurve->wType == TT_PRIM_QSPLINE)
                {
                    // Decode each Quadratic B-Spline segment, convert to bezier,
                    // and append to the Bezier segments
                    cTotal += AppendQuadBSplineToBezier( &pt[cTotal], ptStart, lpCurve );
                    i = lpCurve->cpfx;
                }
                else
                    // Oops! A POLYCURVE format we don't understand.
                    ; // error, error, error

            // Move on to next curve in the contour.
            lpCurve = (LPTTPOLYCURVE)&(lpCurve->apfx[i]);
            }

            // Add points to close the contour.
            // All contours are implied closed by TrueType definition.
            // Depending on the specific font and glyph being used, these
            // may not always be needed.
            if ( pt[cTotal-1].x != pt[0].x || pt[cTotal-1].y != pt[0].y )
            {
                cTotal += CloseContour( pt, cTotal );
            }

            // flip coordinates to get glyph right side up (Windows coordinates)
            // TT native coordiantes are zero originate at lower-left.
            // Windows MM_TEXT are zero originate at upper-left.
            for (i = 0; i < cTotal; i++)
                pt[i].y = 0 - pt[i].y;

            // Draw the contour
            PolyBezier( hDC, pt, cTotal );
        }
        else
            // Bad, bail, must have a bogus buffer.
            break; // error, error, error

        // Move on to next Contour.
        // Its header starts immediate after this contour
        lpHeader = (LPTTPOLYGONHEADER)(((LPSTR)lpHeader) + lpHeader->cb);
    }

    free( pt );
}
				

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Microsoft ???? ???? ??????????? (http://www.microsoft.com/typography/tt/tt.htm)

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???? ID: 243285 - ????? ???????: 02 ?????? 2010 - ??????: 2.0
???? ???? ???? ??:
  • Microsoft Win32 Application Programming Interface
  • Microsoft Windows XP Professional
??????: 
kbdswgdi2003swept kbdraw kbfont kbgdi kbhowto kbmt KB243285 KbMthi
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