Nv Path Rendering fonts optimal implementation - opengl

Question

I'm using NV path rendering having read Getting Started with NV Path Rendering by Mark Kilgard
My implementation is based on the render_font example in the Tiger3DES project in NVidia Graphics Samples.
This implementation seems slower than a normal texture based font solution so I'm wondering is it flawed? NVidia state NV Path rendering is faster than alternatives but I am hitting a performance limit far quicker than I expected.
I have a scene with 1000 'messages'. My FPS is incredibly poor on a Quadro K4200. If I combine the text into a single message there is no performance issue but formatting the messages separately is then impossible. If I reduce the number of messages to 100 I get a decent framerate (200+ unlocked).
Are calls to stencil, coverstroke and coverfill expensive?
Here's a code snippet...
Init FontFace:
/* Create a range of path objects corresponding to Latin-1 character codes. */
m_glyphBase = glGenPathsNV(numChars);
glPathGlyphRangeNV(m_glyphBase,
target,
name.c_str(),
style,
0,
numChars,
GL_USE_MISSING_GLYPH_NV,
pathParamTemplate,
GLfloat(emScale)
);
/* Load base character set for unsupported glyphs. */
glPathGlyphRangeNV(m_glyphBase,
GL_STANDARD_FONT_NAME_NV,
"Sans",
style,
0,
numChars,
GL_USE_MISSING_GLYPH_NV,
pathParamTemplate,
GLfloat(emScale)
);
/* Query font and glyph metrics. */
GLfloat fontData[4];
glGetPathMetricRangeNV(GL_FONT_Y_MIN_BOUNDS_BIT_NV | GL_FONT_Y_MAX_BOUNDS_BIT_NV |
GL_FONT_UNDERLINE_POSITION_BIT_NV | GL_FONT_UNDERLINE_THICKNESS_BIT_NV,
m_glyphBase + ' ',
/*count*/1,
4 * sizeof(GLfloat),
fontData
);
m_yMin = fontData[0];
m_yMax = fontData[1];
m_underlinePosition = fontData[2];
m_underlineThickness = fontData[3];
glGetPathMetricRangeNV(GL_GLYPH_HORIZONTAL_BEARING_ADVANCE_BIT_NV,
m_glyphBase,
numChars,
0, /* stride of zero means sizeof(GLfloat) since 1 bit in mask */
&m_horizontalAdvance[0]
);
Init Message:
glGetPathSpacingNV(GL_ACCUM_ADJACENT_PAIRS_NV,
(GLsizei)message.size(),
GL_UNSIGNED_BYTE,
message.c_str(),
m_font->glyphBase(),
1.0, 1.0,
GL_TRANSLATE_X_NV,
&m_xtranslate[1]
);
/* Total advance is accumulated spacing plus horizontal advance of
the last glyph */
m_totalAdvance = m_xtranslate[m_messageLength - 1] +
m_font->horizontalAdvance(uint32(message[m_messageLength - 1]));
Draw Message:
glStencilStrokePathInstancedNV((GLsizei)m_messageLength,
GL_UNSIGNED_BYTE,
message().c_str(),
font()->glyphBase(),
1, ~0U, /* Use all stencil bits */
GL_TRANSLATE_X_NV,
&m_xtranslate[0]
);
glColor3f(m_colour.r, m_colour.g, m_colour.b);
glCoverStrokePathInstancedNV((GLsizei)m_messageLength,
GL_UNSIGNED_BYTE,
message().c_str(),
font()->glyphBase(),
GL_BOUNDING_BOX_OF_BOUNDING_BOXES_NV,
GL_TRANSLATE_X_NV,
&m_xtranslate[0]
);
glStencilFillPathInstancedNV((GLsizei)m_messageLength,
GL_UNSIGNED_BYTE,
message().c_str(),
font()->glyphBase(),
GL_PATH_FILL_MODE_NV,
~0U, /* Use all stencil bits */
GL_TRANSLATE_X_NV,
&m_xtranslate[0]
);
glCoverFillPathInstancedNV((GLsizei)m_messageLength,
GL_UNSIGNED_BYTE,
message().c_str(),
font()->glyphBase(),
GL_BOUNDING_BOX_OF_BOUNDING_BOXES_NV,
GL_TRANSLATE_X_NV,
&m_xtranslate[0]
);

Answer 1

I located the cause of the slowness and it wasn't related to the above referenced functions. These functions perform very well once the offending code was removed. Full disclosure - I was using std::stack for the matrices used in the scene and calls to push and pop on the stack were expensive. So in answer to the question NVidia path rendering for text is blisteringly fast and stencil, coverstroke and coverfill are inexpensive.