wglUseFontOutlines
[New
- Windows 95, OEM Service Release 2]
The wglUseFontOutlines
function creates a set of display lists, one for each glyph of the
currently selected outline font of a device context, for use with the current
rendering context. The display lists are used to draw 3-D characters of
TrueType fonts. Each display list describes a glyph outline in floating-point
coordinates.
The run of
glyphs begins with the first glyph of the font of the specified device
context. The em square size of the font, the notional grid size of the original
font outline from which the font is fitted, is mapped to 1.0 in the x- and
y-coordinates in the display lists. The extrusion parameter sets how much depth
the font has in the z direction.
The lpgmf
parameter returns a GLYPHMETRICSFLOAT structure that contains information about the
placement and orientation of each glyph in a character cell.
BOOL wglUseFontOutlines(
|
HDC hdc, |
// device
context of the outline font |
|
DWORD first, |
// first
glyph to be turned into a display list |
|
DWORD count, |
// number
of glyphs to be turned into display lists |
|
DWORD listBase, |
//
specifies the starting display list |
|
FLOAT deviation, |
//
specifies the maximum chordal deviation from the true outlines |
|
FLOAT extrusion, |
//
extrusion value in the negative z direction |
|
int format, |
//
specifies line segments or polygons in display lists |
|
LPGLYPHMETRICSFLOAT lpgmf
|
// address
of buffer to receive glyph metric data |
|
); |
|
Parameters
hdc
Specifies the
device context with the desired outline font. The outline font of hdc is
used to create the display lists in the current rendering context.
first
Specifies the
first of the set of glyphs that form the font outline display lists.
count
Specifies the
number of glyphs in the set of glyphs used to form the font outline display
lists. The wglUseFontOutlines function creates count display
lists, one display list for each glyph in a set of glyphs.
listBase
Specifies a
starting display list.
deviation
Specifies the
maximum chordal deviation from the original outlines. When deviation is zero,
the chordal deviation is equivalent to one design unit of the original font.
The value of deviation must be equal to or greater than 0.
extrusion
Specifies how
much a font is extruded in the negative z direction. The value must be
equal to or greater than 0. When extrusion is 0, the display lists are
not extruded.
format
Specifies the
format, either WGL_FONT_LINES or WGL_FONT_POLYGONS, to use in the display
lists. When format is WGL_FONT_LINES, the wglUseFontOutlines
function creates fonts with line segments. When format is
WGL_FONT_POLYGONS, wglUseFontOutlines creates fonts with polygons.
lpgmf
Points to an
array of count GLYPHMETRICSFLOAT structures that is to receive the metrics of
the glyphs. When lpgmf is NULL, no glyph metrics are returned.
Return Values
When the
function succeeds, the return value is TRUE.
When the
function fails, the return value is FALSE and no display lists are generated.
To get extended error information, call GetLastError.
Remarks
The
wglUseFontOutlines function defines the glyphs of an outline font with
display lists in the current rendering context. The wglUseFontOutlines
function works with TrueType fonts only; stroke and raster fonts are not
supported.
Each display
list consists of either line segments or polygons, and has a unique identifying
number starting with the listBase number.
The wglUseFontOutlines
function approximates glyph outlines by subdividing the quadratic B-spline
curves of the outline into line segments, until the distance between the
outline and the interpolated midpoint is within the value specified by deviation.
This is the final format used when format is WGL_FONT_LINES. When you
specify WGL_FONT_OUTLINES, the display lists created don t contain any normals;
thus lighting doesn t work properly. To get the correct lighting of lines use
WGL_FONT_POLYGONS and set glPolygonMode(GL_FRONT, GL_LINE). When
you specify format as WGL_FONT_POLYGONS the outlines are further
tessellated into separate triangles, triangle fans, triangle strips, or
quadrilateral strips to create the surface of each glyph. With
WGL_FONT_POLYGONS, the created display lists call glFrontFace(GL_CW)
or glFrontFace(GL_CCW); thus the current front-face value might
be altered. For the best appearance of text with WGL_FONT_POLYGONS, cull the
back faces as follows:
glCullFace(GL_BACK);
glEnable(GL_CULL_FACE);
A GLYPHMETRICSFLOAT
structure contains information about the placement and orientation of each
glyph in a character cell. The lpgmf parameter is an array of GLYPHMETRICSFLOAT
structures holding the entire set of glyphs for a font. Each display list ends
with a translation specified with the gmfCellIncX and gmfCellIncY
members of the corresponding GLYPHMETRICSFLOAT structure. The
translation enables the drawing of successive characters in their natural
direction with a single call to glCallLists.
Note With the
current release of OpenGL for Windows NT and Windows 95, you cannot make GDI
calls to a device context when a pixel format is double-buffered. You can work
around this limitation by using wglUseFontOutlines and wglUseFontBitmaps, when using
double-buffered device contexts.
The following
code example shows how to draw text using wglUseFontOutlines:
HDC
hdc; // A TrueType font has
already been selected
HGLRC hglrc;
GLYPHMETRICSFLOAT agmf[256];
// Make hglrc the calling thread's current rendering
context
wglMakeCurrent(hdc, hglrc);
// create display lists for glyphs 0 through 255
with 0.1 extrusion
// and default deviation. The display list numbering
starts at 1000
// (it could be any number)
wglUseFontOutlines(hdc, 0, 255, 1000, 0.0f, 0.1f,
WGL_FONT_POLYGONS, &agmf);
// Set up transformation to draw the string
glLoadIdentity();
glTranslate(0.0f, 0.0f, -5.0f)
glScalef(2.0f, 2.0f, 2.0f);
// Display a string
glListBase(1000); // Indicates the start of display
lists for the glyphs
// Draw the characters in a string
glCallLists(24, GL_UNSIGNED_BYTE, "Hello Win32
OpenGL World.");
See Also