Q87115: HOWTO: GetGlyphOutline() Native Buffer Format
Article: Q87115
Product(s): Microsoft Windows Software Development Kit
Version(s): 3.1,3.5,3.51,4.0,95
Operating System(s):
Keyword(s): kbOSWinNT350 kbOSWinNT351 kbOSWinNT400 kbOSWin95 kbSDKWin16
Last Modified: 12-MAY-2001
-------------------------------------------------------------------------------
The information in this article applies to:
- Microsoft Windows Software Development Kit (SDK) 3.1
- Microsoft Win32 Application Programming Interface (API)
-------------------------------------------------------------------------------
SUMMARY
=======
The GetGlyphOutline function provides a method for an application to retrieve
the lowest-level information about a glyph in the TrueType environment. This
article describes the format of the data the GetGlyphOutline function returns.
MORE INFORMATION
================
A glyph outline is a series of contours that describe the glyph. Each contour is
defined by a TTPOLYGONHEADER data structure, which is followed by as many
TTPOLYCURVE data structures as are required to describe the contour.
Each position is described by a POINTFX data structure, which represents an
absolute position, not a relative position. The starting and ending point for
the glyph is given by the pfxStart member of the TTPOLYGONHEADER data
structure.
The TTPOLYCURVE data structures fall into two types: a TT_PRIM_LINE record or a
TT_PRIM_QSPLINE record. A TT_PRIM_LINE record is a series of points; lines drawn
between the points describe the outline of the glyph. A TT_PRIM_QSPLINE record
is a series of points defining the quadratic splines (q-splines) required to
describe the outline of the character.
In TrueType, a q-spline is defined by three points (A, B, and C), where points A
and C are on the curve and point B is off the curve. The equation for each
q-spline is as follows (xA represents the x-coordinate of point A, yA represents
the y-coordinate of point A, and so on)
x(t) = (xA-2xB+xC)*t^2 + (2xB-2xA)*t + xA
y(t) = (yA-2yB+yC)*t^2 + (2yB-2yA)*t + yA
where t varies from 0.0 to 1.0.
The format of a TT_PRIM_QSPLINE record is as follows:
- Point A on the q-spline is the current position (either pfxStart in the
TTPOLYGONHEADER, the starting point for the TTPOLYCURVE, or the ending point
of the previous TTPOLYCURVE).
- Point B is the current point in the record.
- Point C is as follows:
- If the record has two or more points following point B, point C is the
midpoint between point B and the next point in the record.
- Otherwise, point C is the point following point B.
The following code presents the algorithm used to process a TT_PRIM_QSPLINE
record. While this code demonstrates how to extract q-splines from a
TT_PRIM_QSPLINE record, it is not appropriate for use in an application.
pfxA = pfxStart; // Starting point for this polygon
for (u = 0; u < cpfx - 1; u++) // Walk through points in spline
{
pfxB = apfx[u]; // B is always the current point
if (u < cpfx - 2) // If not on last spline, compute C
{
pfxC.x = (pfxB.x + apfx[u+1].x) / 2; // x midpoint
pfxC.y = (pfxB.y + apfx[u+1].y) / 2; // y midpoint
}
else // Else, next point is C
pfxC = apfx[u+1];
// Draw q-spline
DrawQSpline(hdc, pfxA, pfxB, pfxC);
pfxA = pfxC; // Update current point
}
The algorithm above manipulates points directly, using floating-point operators.
However, points in q-spline records are stored in a FIXED data type. The
following code demonstrates how to manipulate FIXED data items:
FIXED fx;
long *pl = (long *)&fx;
// Perform all arithmetic on *pl rather than on fx
*pl = *pl / 2;
The following function converts a floating-point number into the FIXED
representation:
FIXED FixedFromDouble(double d)
{
long l;
l = (long) (d * 65536L);
return *(FIXED *)&l;
}
In a production application, rather than writing a DrawQSpline function to draw
each q-spline individually, it is more efficient to calculate points on the
q-spline and store them in an array of POINT data structures. When the
calculations for a glyph are complete, pass the POINT array to the PolyPolygon
function to draw and fill the glyph.
The following example presents the data returned by the GetGlyphOutline for the
lowercase "j" glyph in the 24-point Arial font of the 8514/a (Small Fonts) video
driver:
GetGlyphOutline GGO_NATIVE 'j'
dwrc = 208 // Total native buffer size in bytes
gmBlackBoxX, Y = 6, 29 // Dimensions of black part of glyph
gmptGlyphOrigin = -1, 23 // Lower-left corner of glyph
gmCellIncX, Y = 7, 0 // Vector to next glyph origin
TTPOLYGONHEADER #1 // Contour for dot on "j"
cb = 44 // Total size of dot polygon
dwType = 24 // TT_POLYGON_TYPE
pfxStart = 2.000, 20.000 // Start at lower-left corner of dot
TTPOLYCURVE #1
wType = TT_PRIM_LINE
cpfx = 3
pfx[0] = 2.000, 23.000
pfx[1] = 5.000, 23.000
pfx[2] = 5.000, 20.000 // Automatically close to pfxStart
TTPOLYGONHEADER #2 // Contour for body of "j"
cb = 164 // Total size is 164 bytes
dwType = 24 // TT_POLYGON_TYPE
pfxStart = -1.469, -5.641
TTPOLYCURVE #1 // Finish flat bottom end of "j"
wType = TT_PRIM_LINE
cpfx = 1
pfx[0] = -0.828, -2.813
TTPOLYCURVE #2 // Make hook in "j" with spline
// Point A in spline is end of TTPOLYCURVE #1
wType = TT_PRIM_QSPLINE
cpfx = 2 // two points in spline -> one curve
pfx[0] = -0.047, -3.000 // This is point B in spline
pfx[1] = 0.406, -3.000 // Last point is always point C
TTPOLYCURVE #3 // Finish hook in "j"
// Point A in spline is end of TTPOLYCURVE #2
wType = TT_PRIM_QSPLINE
cpfx = 3 // Three points -> two splines
pfx[0] = 1.219, -3.000 // Point B for first spline
// Point C is (pfx[0] + pfx[1]) / 2
pfx[1] = 2.000, -1.906 // Point B for second spline
pfx[2] = 2.000, 0.281 // Point C for second spline
TTPOLYCURVE #4 // Majority of "j" outlined by this polyline
wType = TT_PRIM_LINE
cpfx = 3
pfx[0] = 2.000, 17.000
pfx[1] = 5.000, 17.000
pfx[2] = 5.000, -0.250
TTPOLYCURVE #5 // start of bottom of hook
wType = TT_PRIM_QSPLINE
cpfx = 2 // One spline in this polycurve
pfx[0] = 5.000, -3.266 // Point B for spline
pfx[1] = 4.188, -4.453 // Point C for spline
TTPOLYCURVE #6 // Middle of bottom of hook
wType = TT_PRIM_QSPLINE
cpfx = 2 // One spline in this polycurve
pfx[0] = 3.156, -6.000 // B for spline
pfx[1] = 0.766, -6.000 // C for spline
TTPOLYCURVE #7 // Finish bottom of hook and glyph
wType = TT_PRIM_QSPLINE
cpfx = 2 // One spline in this polycurve
pfx[0] = -0.391, -6.000 // B for spline
pfx[1] = -1.469, -5.641 // C for spline
Additional query words:
======================================================================
Keywords : kbOSWinNT350 kbOSWinNT351 kbOSWinNT400 kbOSWin95 kbSDKWin16
Technology : kbAudDeveloper kbWin3xSearch kbSDKSearch kbWin32sSearch kbWin32API kbWinSDKSearch kbWinSDK310
Version : :3.1,3.5,3.51,4.0,95
Issue type : kbhowto
=============================================================================
THE INFORMATION PROVIDED IN THE MICROSOFT KNOWLEDGE BASE IS PROVIDED "AS IS" WITHOUT WARRANTY OF ANY KIND. MICROSOFT DISCLAIMS ALL WARRANTIES, EITHER EXPRESS OR IMPLIED, INCLUDING THE WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE. IN NO EVENT SHALL MICROSOFT CORPORATION OR ITS SUPPLIERS BE LIABLE FOR ANY DAMAGES WHATSOEVER INCLUDING DIRECT, INDIRECT, INCIDENTAL, CONSEQUENTIAL, LOSS OF BUSINESS PROFITS OR SPECIAL DAMAGES, EVEN IF MICROSOFT CORPORATION OR ITS SUPPLIERS HAVE BEEN ADVISED OF THE POSSIBILITY OF SUCH DAMAGES. SOME STATES DO NOT ALLOW THE EXCLUSION OR LIMITATION OF LIABILITY FOR CONSEQUENTIAL OR INCIDENTAL DAMAGES SO THE FOREGOING LIMITATION MAY NOT APPLY.
Copyright Microsoft Corporation 1986-2002.