📄 fog.html
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<HTML><BODY><PRE> <STRONG>NAME</STRONG> <STRONG>glFogf,</STRONG> <STRONG>glFogi,</STRONG> <STRONG>glFogfv,</STRONG> <STRONG>glFogiv</STRONG> - specify fog parameters <STRONG>C</STRONG> <STRONG>SPECIFICATION</STRONG> void <STRONG>glFogf</STRONG>( GLenum <EM>pname</EM>, GLfloat <EM>param</EM> ) void <STRONG>glFogi</STRONG>( GLenum <EM>pname</EM>, GLint <EM>param</EM> ) <STRONG>PARAMETERS</STRONG> <EM>pname</EM> Specifies a single-valued fog parameter. <STRONG>GL_FOG_MODE</STRONG>, <STRONG>GL_FOG_DENSITY</STRONG>, <STRONG>GL_FOG_START</STRONG>, <STRONG>GL_FOG_END</STRONG>, and <STRONG>GL_FOG_INDEX</STRONG> are accepted. <EM>param</EM> Specifies the value that <EM>pname</EM> will be set to. <STRONG>C</STRONG> <STRONG>SPECIFICATION</STRONG> void <STRONG>glFogfv</STRONG>( GLenum <EM>pname</EM>, const GLfloat *<EM>params</EM> ) void <STRONG>glFogiv</STRONG>( GLenum <EM>pname</EM>, const GLint *<EM>params</EM> ) <STRONG>PARAMETERS</STRONG> <EM>pname</EM> Specifies a fog parameter. <STRONG>GL_FOG_MODE</STRONG>, <STRONG>GL_FOG_DENSITY</STRONG>, <STRONG>GL_FOG_START</STRONG>, <STRONG>GL_FOG_END</STRONG>, <STRONG>GL_FOG_INDEX</STRONG>, and <STRONG>GL_FOG_COLOR</STRONG> are accepted. <EM>params</EM> Specifies the value or values to be assigned to <EM>pname</EM>. <STRONG>GL_FOG_COLOR</STRONG> requires an array of four values. All other parameters accept an array containing only a single value. <STRONG>DESCRIPTION</STRONG> Fog is initially disabled. While enabled, fog affects rasterized geometry, bitmaps, and pixel blocks, but not buffer clear operations. To enable and disable fog, call <STRONG>glEnable</STRONG> and <STRONG>glDisable</STRONG> with argument <STRONG>GL_FOG</STRONG>. <STRONG>glFog</STRONG> assigns the value or values in <EM>params</EM> to the fog parameter specified by <EM>pname</EM>. The following values are accepted for <EM>pname</EM>: <STRONG>GL_FOG_MODE</STRONG> <EM>params</EM> is a single integer or floating- point value that specifies the equation to be used to compute the fog blend factor, f. Three symbolic constants are accepted: <STRONG>GL_LINEAR</STRONG>, <STRONG>GL_EXP</STRONG>, and <STRONG>GL_EXP2</STRONG>. The equations corresponding to these symbolic constants are defined below. The initial fog mode is <STRONG>GL_EXP</STRONG>. <STRONG>GL_FOG_DENSITY</STRONG> <EM>params</EM> is a single integer or floating- point value that specifies density, the fog density used in both exponential fog equations. Only nonnegative densities are accepted. The initial fog density is 1. <STRONG>GL_FOG_START</STRONG> <EM>params</EM> is a single integer or floating- point value that specifies start, the near distance used in the linear fog equation. The initial near distance is 0. <STRONG>GL_FOG_END</STRONG> <EM>params</EM> is a single integer or floating- point value that specifies end, the far distance used in the linear fog equation. The initial far distance is 1. <STRONG>GL_FOG_INDEX</STRONG> <EM>params</EM> is a single integer or floating- point value that specifies i , the fog color index. The initial fo<STRONG>g</STRONG> index is 0. <STRONG>GL_FOG_COLOR</STRONG> <EM>params</EM> contains four integer or floating-point values that specify C , the fog color. Integer values are f mapped linearly such that the most positive representable value maps to 1.0, and the most negative representable value maps to -1.0. Floating-point values are mapped directly. After conversion, all color components are clamped to the range [0,1]. The initial fog color is (0, 0, 0, 0). Fog blends a fog color with each rasterized pixel fragment's posttexturing color using a blending factor f. Factor f is computed in one of three ways, depending on the fog mode. Let z be the distance in eye coordinates from the origin to the fragment being fogged. The equation for <STRONG>GL_LINEAR</STRONG> fog is f = __<STRONG>___</STRONG>_<STRONG>_</STRONG>_<STRONG>_</STRONG>__ end - start The equation for <STRONG>GL_EXP</STRONG> fog is f = e**(-(density . z)) The equation for <STRONG>GL_EXP2</STRONG> fog is f = e**(-(density . z)**2) Regardless of the fog mode, f is clamped to the range [0,1] after it is computed. Then, if the GL is in RGBA color mode, the fragment's color C is replaced by r C ' = fC +(1-f)C r r f In color index mode, the fragment's color index i is replaced by r i ' = i +(1-f)i r r f <STRONG>ERRORS</STRONG> <STRONG>GL_INVALID_ENUM</STRONG> is generated if <EM>pname</EM> is not an accepted value, or if <EM>pname</EM> is <STRONG>GL_FOG_MODE</STRONG> and <EM>params</EM> is not an accepted value. <STRONG>GL_INVALID_VALUE</STRONG> is generated if <EM>pname</EM> is <STRONG>GL_FOG_DENSITY</STRONG>, and <EM>params</EM> is negative. <STRONG>GL_INVALID_OPERATION</STRONG> is generated if <STRONG>glFog</STRONG> is executed between the execution of <STRONG>glBegin</STRONG> and the corresponding execution of <STRONG>glEnd</STRONG>. <STRONG>ASSOCIATED</STRONG> <STRONG>GETS</STRONG> <STRONG>glIsEnabled</STRONG> with argument <STRONG>GL_FOG</STRONG> <STRONG>glGet</STRONG> with argument <STRONG>GL_FOG_COLOR</STRONG> <STRONG>glGet</STRONG> with argument <STRONG>GL_FOG_INDEX</STRONG> <STRONG>glGet</STRONG> with argument <STRONG>GL_FOG_DENSITY</STRONG> <STRONG>glGet</STRONG> with argument <STRONG>GL_FOG_START</STRONG> <STRONG>glGet</STRONG> with argument <STRONG>GL_FOG_END</STRONG> <STRONG>glGet</STRONG> with argument <STRONG>GL_FOG_MODE</STRONG> <STRONG>SEE</STRONG> <STRONG>ALSO</STRONG> <STRONG>glEnable</STRONG></PRE></BODY></HTML>⌨️ 快捷键说明
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