B
glBegin
Chapter 2
20
glBegin
glBegin, glEnd: delimit the vertices of a primitive or a group of like primitives.
C Specification
void glBegin(
GLenum mode)
void glEnd(void)
Parameters
mode Specifies the primitive or primitives that will be created from vertices
presented between glBegin and the subsequent glEnd. Ten symbolic
constants are accepted:
GL_POINTS, GL_LINES, GL_LINE_STRIP, GL_LINE_LOOP,
GL_TRIANGLES, GL_TRIANGLE_STRIP, GL_TRIANGLE_FAN,
GL_QUADS, GL_QUAD_STRIP, and GL_POLYGON.
Description
glBegin and glEnd delimit the vertices that define a primitive or a group of like
primitives. glBegin accepts a single argument that specifies in which of ten ways the
vertices are interpreted. Taking n as an integer count starting at one, and n as the total
number of vertices specified, the interpretations are as follows:
GL_POINTS Treats each vertex as a single point. Vertex n defines point n. n points
are drawn.
GL_LINES Treats each pair of vertices as an independent line segment. Vertices
2
n
- 1 and 2
n
define line n. n/2 lines are drawn.
GL_LINE_STRIP
Draws a connected group of line segments from the first vertex to the
last. n - 1 lines are drawn.
GL_LINE_LOOP
Draws a connected group of line segments from the first vertex to the
last, then back to the first. Vertices n and n+1 define line n. The last
line, however, is defined by vertices n and 1. n lines are drawn.
GL_TRIANGLES
Treats each triplet of vertices as an independent triangle. Vertices 3n-
2, 3n - 1, and 3n define triangle n. n/3 triangles are drawn.
GL_TRIANGLE_STRIP
Draws a connected group of triangles. One triangle is defined for each
vertex presented after the first two vertices. For odd n, vertices n, n+1,
and n+2 define triangle n. For even n, vertices n+1, n, and n+2 define
triangle n. n2 triangles are drawn.
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