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<HTML><BODY><PRE> <STRONG>NAME</STRONG> <STRONG>fglBegin,</STRONG> <STRONG>fglEnd</STRONG> - delimit the vertices of a primitive or a group of like primitives <STRONG>FORTRAN</STRONG> <STRONG>SPECIFICATION</STRONG> SUBROUTINE <STRONG>fglBegin</STRONG>( INTEGER*4 <EM>mode</EM> ) <STRONG>PARAMETERS</STRONG> <EM>mode</EM> Specifies the primitive or primitives that will be created from vertices presented between <STRONG>fglBegin</STRONG> and the subsequent <STRONG>fglEnd</STRONG>. Ten symbolic constants are accepted: <STRONG>GL_POINTS</STRONG>, <STRONG>GL_LINES</STRONG>, <STRONG>GL_LINE_STRIP</STRONG>, <STRONG>GL_LINE_LOOP</STRONG>, <STRONG>GL_TRIANGLES</STRONG>, <STRONG>GL_TRIANGLE_STRIP</STRONG>, <STRONG>GL_TRIANGLE_FAN</STRONG>, <STRONG>GL_QUADS</STRONG>, <STRONG>GL_QUAD_STRIP</STRONG>, and <STRONG>GL_POLYGON</STRONG>. <STRONG>FORTRAN</STRONG> <STRONG>SPECIFICATION</STRONG> SUBROUTINE <STRONG>fglEnd</STRONG>( ) <STRONG>DESCRIPTION</STRONG> <STRONG>fglBegin</STRONG> and <STRONG>fglEnd</STRONG> delimit the vertices that define a primitive or a group of like primitives. <STRONG>fglBegin</STRONG> accepts a single argument that specifies in which of ten ways the vertices are interpreted. Taking <EM>n</EM> as an integer count starting at one, and <EM>N</EM> as the total number of vertices specified, the interpretations are as follows: <STRONG>GL_POINTS</STRONG> Treats each vertex as a single point. Vertex <EM>n</EM> defines point <EM>n</EM>. <EM>N</EM> points are drawn. <STRONG>GL_LINES</STRONG> Treats each pair of vertices as an independent line segment. Vertices <EM>2n</EM>-<EM>1</EM> and <EM>2n</EM> define line <EM>n</EM>. <EM>N</EM>/<EM>2</EM> lines are drawn. <STRONG>GL_LINE_STRIP</STRONG> Draws a connected group of line segments from the first vertex to the last. Vertices <EM>n</EM> and <EM>n</EM>+<EM>1</EM> define line <EM>n</EM>. <EM>N</EM>-<EM>1</EM> lines are drawn. <STRONG>GL_LINE_LOOP</STRONG> Draws a connected group of line segments from the first vertex to the last, then back to the first. Vertices <EM>n</EM> and <EM>n</EM>+<EM>1</EM> define line <EM>n</EM>. The last line, however, is defined by vertices <EM>N</EM> and <EM>1</EM>. <EM>N</EM> lines are drawn. <STRONG>GL_TRIANGLES</STRONG> Treats each triplet of vertices as an independent triangle. Vertices <EM>3n</EM>-<EM>2</EM>, <EM>3n</EM>-<EM>1</EM>, and <EM>3n</EM> define triangle <EM>n</EM>. <EM>N</EM>/<EM>3</EM> triangles are drawn. <STRONG>GL_TRIANGLE_STRIP</STRONG> Draws a connected group of triangles. One triangle is defined for each vertex presented after the first two vertices. For odd <EM>n</EM>, vertices <EM>n</EM>, <EM>n</EM>+<EM>1</EM>, and <EM>n</EM>+<EM>2</EM> define triangle <EM>n</EM>. For even <EM>n</EM>, vertices <EM>n</EM>+<EM>1</EM>, <EM>n</EM>, and <EM>n</EM>+<EM>2</EM> define triangle <EM>n</EM>. <EM>N</EM>-<EM>2</EM> triangles are drawn. <STRONG>GL_TRIANGLE_FAN</STRONG> Draws a connected group of triangles. One triangle is defined for each vertex presented after the first two vertices. Vertices <EM>1</EM>, <EM>n</EM>+<EM>1</EM>, and <EM>n</EM>+<EM>2</EM> define triangle <EM>n</EM>. <EM>N</EM>-<EM>2</EM> triangles are drawn. <STRONG>GL_QUADS</STRONG> Treats each group of four vertices as an independent quadrilateral. Vertices <EM>4n</EM>-<EM>3</EM>, <EM>4n</EM>-<EM>2</EM>, <EM>4n</EM>-<EM>1</EM>, and <EM>4n</EM> define quadrilateral <EM>n</EM>. <EM>N</EM>/<EM>4</EM> quadrilaterals are drawn. <STRONG>GL_QUAD_STRIP</STRONG> Draws a connected group of quadrilaterals. One quadrilateral is defined for each pair of vertices presented after the first pair. Vertices <EM>2n</EM>-<EM>1</EM>, <EM>2n</EM>, <EM>2n</EM>+<EM>2</EM>, and <EM>2n</EM>+<EM>1</EM> define quadrilateral <EM>n</EM>. <EM>N</EM>/<EM>2</EM>-<EM>1</EM> quadrilaterals are drawn. Note that the order in which vertices are used to construct a quadrilateral from strip data is different from that used with independent data. <STRONG>GL_POLYGON</STRONG> Draws a single, convex polygon. Vertices <EM>1</EM> through <EM>N</EM> define this polygon. Only a subset of GL commands can be used between <STRONG>fglBegin</STRONG> and <STRONG>fglEnd</STRONG>. The commands are <STRONG>fglVertex</STRONG>, <STRONG>fglColor</STRONG>, <STRONG>fglIndex</STRONG>, <STRONG>fglNormal</STRONG>, <STRONG>fglTexCoord</STRONG>, <STRONG>fglEvalCoord</STRONG>, <STRONG>fglEvalPoint</STRONG>, <STRONG>fglArrayElement</STRONG>, <STRONG>fglMaterial</STRONG>, and <STRONG>fglEdgeFlag</STRONG>. Also, it is acceptable to use <STRONG>fglCallList</STRONG> or <STRONG>fglCallLists</STRONG> to execute display lists that include only the preceding commands. If any other GL command is executed between <STRONG>fglBegin</STRONG> and <STRONG>fglEnd</STRONG>, the error flag is set and the command is ignored. Regardless of the value chosen for <EM>mode</EM>, there is no limit to the number of vertices that can be defined between <STRONG>fglBegin</STRONG> and <STRONG>fglEnd</STRONG>. Lines, triangles, quadrilaterals, and polygons that are incompletely specified are not drawn. Incomplete specification results when either too few vertices are provided to specify even a single primitive or when an incorrect multiple of vertices is specified. The incomplete primitive is ignored; the rest are drawn. The minimum specification of vertices for each primitive is as follows: 1 for a point, 2 for a line, 3 for a triangle, 4 for a quadrilateral, and 3 for a polygon. Modes that require a certain multiple of vertices are <STRONG>GL_LINES</STRONG> (2), <STRONG>GL_TRIANGLES</STRONG> (3), <STRONG>GL_QUADS</STRONG> (4), and <STRONG>GL_QUAD_STRIP</STRONG> (2). <STRONG>ERRORS</STRONG> <STRONG>GL_INVALID_ENUM</STRONG> is generated if <EM>mode</EM> is set to an unaccepted value. <STRONG>GL_INVALID_OPERATION</STRONG> is generated if <STRONG>fglBegin</STRONG> is executed between a <STRONG>fglBegin</STRONG> and the corresponding execution of <STRONG>fglEnd</STRONG>. <STRONG>GL_INVALID_OPERATION</STRONG> is generated if <STRONG>fglEnd</STRONG> is executed without being preceded by a <STRONG>fglBegin</STRONG>. <STRONG>GL_INVALID_OPERATION</STRONG> is generated if a command other than <STRONG>fglVertex</STRONG>, <STRONG>fglColor</STRONG>, <STRONG>fglIndex</STRONG>, <STRONG>fglNormal</STRONG>, <STRONG>fglTexCoord</STRONG>, <STRONG>fglEvalCoord</STRONG>, <STRONG>fglEvalPoint</STRONG>, <STRONG>fglArrayElement</STRONG>, <STRONG>fglMaterial</STRONG>, <STRONG>fglEdgeFlag</STRONG>, <STRONG>fglCallList</STRONG>, or <STRONG>fglCallLists</STRONG> is executed between the execution of <STRONG>fglBegin</STRONG> and the corresponding execution <STRONG>fglEnd</STRONG>. Execution of <STRONG>fglEnableClientState</STRONG>, <STRONG>fglDisableClientState</STRONG>, <STRONG>fglEdgeFlagPointer</STRONG>, <STRONG>fglTexCoordPointer</STRONG>, <STRONG>fglColorPointer</STRONG>, <STRONG>fglIndexPointer</STRONG>, <STRONG>fglNormalPointer</STRONG>, <STRONG>fglVertexPointer</STRONG>, <STRONG>fglInterleavedArrays</STRONG>, or <STRONG>fglPixelStore</STRONG> is not allowed after a call to <STRONG>fglBegin</STRONG> and before the corresponding call to <STRONG>fglEnd</STRONG>, but an error may or may not be generated. <STRONG>SEE</STRONG> <STRONG>ALSO</STRONG> <STRONG>fglArrayElement</STRONG>, <STRONG>fglCallList</STRONG>, <STRONG>fglCallLists</STRONG>, <STRONG>fglColor</STRONG>, <STRONG>fglEdgeFlag</STRONG>, <STRONG>fglEvalCoord</STRONG>, <STRONG>fglEvalPoint</STRONG>, <STRONG>fglIndex</STRONG>, <STRONG>fglMaterial</STRONG>, <STRONG>fglNormal</STRONG>, <STRONG>fglTexCoord</STRONG>, <STRONG>fglVertex</STRONG></PRE></BODY></HTML>⌨️ 快捷键说明
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