HP Workstation zx2000 OpenGL 1.1 Reference for HP-UX 11.x - Page 20

B glBegin 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 2n - 1 and 2n 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. 20 Chapter 2