Geometry Shader Concepts and Examples - Graphics Shaders - page 296

2. The primitive type that is to be sent to the geometry shader is given by
glProgramParameteri( progname,
GL_GEOMETRY_INPUT_TYPE, intvalue)
where intvalue is a symbolic parameter for the primitive type that this
geometry shader will be receiving. This parameter can take on any one of
the five symbolic values
• GL_POINTS
• GL_LINES
• GL_LINES_ADJACENCY
• GL_TRIANGLES
• GL_TRIANGLES_ADJACENCY
The kind of graphics primitive that can be passed to the geometry
shader depends on the kind of geometry that the shader is to emit.
• If GL_LINES is chosen, the lines could actually come from GL_LINES ,
GL_LINE_STRIP , or GL_LINE_LOOP .
• If GL_LINES_ADJACENCY is chosen, the lines with adjacency could
actually come from GL_LINES_ADJACENCY or GL_LINE_STRIP_
ADJACENCY .
• If GL_TRIANGLES is chosen, the triangles could actually come from
GL_TRIANGLES , GL_TRIANGLE_STRIP , GL_TRIANGLE_FAN , GL_QUADS , or
GL_QUAD_STRIP .
• If GL_TRIANGLES_ADJACENCY is chosen, the triangles with adja-
cency could actually come from GL_TRIANGLES_ADJACENCY or GL_
TRIANGLE_STRIP_ADJACENCY .
3. The actual primitive type that is to be emited from the geometry shader
is given by
glProgramParameteri(progname,
GL_GEOMETRY_OUTPUT_TYPE, intvalue)
where intvalue is a symbolic parameter for the primitive type that the
geometry shader will be emiting. This parameter can take on the sym-
bolic values
• GL_POINTS
• GL_LINE_STRIP
• GL_TRIANGLE_STRIP