wglUseFontOutlinesA function (wingdi.h)

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 thefirstglyph 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.

Thelpgmfparameter returns a GLYPHMETRICSFLOAT structure that contains information about the placement and orientation of each glyph in a character cell.

Syntax

BOOL wglUseFontOutlinesA(
  HDC                 unnamedParam1,
  DWORD               unnamedParam2,
  DWORD               unnamedParam3,
  DWORD               unnamedParam4,
  FLOAT               unnamedParam5,
  FLOAT               unnamedParam6,
  int                 unnamedParam7,
  LPGLYPHMETRICSFLOAT unnamedParam8
);

Parameters

unnamedParam1

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.

unnamedParam2

Specifies the first of the set of glyphs that form the font outline display lists.

unnamedParam3

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.

unnamedParam4

Specifies a starting display list.

unnamedParam5

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.

unnamedParam6

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.

unnamedParam7

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.

unnamedParam8

Points to an array of countGLYPHMETRICSFLOAT structures that is to receive the metrics of the glyphs. When lpgmf is NULL, no glyph metrics are returned.

Return value

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.

Examples

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 Windows OpenGL World.");

Requirements

See also

GLYPHMETRICSFLOAT

OpenGL on Windows

WGL Functions

glCallLists

glListBase

glTexGen

wglUseFontBitmaps