Open GL Super Bible:Visual Effects:nBlending and Fog















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Open GL Super Bible


(Publisher: Macmillan Computer Publishing)

Author(s): Waite group Press

ISBN: 1571690735

Publication Date: 08/01/96

 




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Summary
Blending and fog complete the OpenGL library and are yet another source for making the images you generate more realistic. Blending provides transparency effects and improves anti-aliasing of points, lines, and polygons. Fog supports a variety of depth-cueing and weather effects that make images look less exact and, ironically, more like the real world.
Reference Section
glBlendFunc

Purpose
Sets color blending functions.
Include File
<GL/gl.h>
Syntax
void glBlendFunc(GLenum sfactor, GLenum dfactor);
Description
This function sets the source and destination
blending factors for color blending. You must call glEnable(GL_BLEND) to
enable color blending. Blending is only available in RGBA drawing
contexts. The default settings for blending are glBlendFunc(GL_ONE,
GL_ZERO).


Parameters

sfactor

GLenum: The source colorłs blending function.
dfactor

GLenum: The destination pixel colorłs blending function.
Returns
None.
Example
See the example in CH16\BLENDPOT.C on the CD.


glFog

Purpose
Specifies fog parameters.
Include File
<GL/gl.h>
Syntax
void glFogf(GLenum pname, GLfloat param);

void glFogfv(GLenum pname, GLfloat *params);

void glFogi(GLenum pname, GLint param);

void glFogiv(GLenum pname, GLint *params);
Description
The glFog functions
set fog parameters. To draw using fog you must call glEnable(GL_FOG).


Parameters

pname

GLenum: The parameter to set. Valid names are as
follows:





GL_FOG_COLOR
The color of the fog; must be an array of 4 numbers representing the RGBA color.

GL_FOG_DENSITY
The fog density; a number greater than 0.0. The density is only used for the GL_EXP and GL_EXP2 fog modes.

GL_FOG_END
The farthest distance to which the fog is applied. This is a transformed Z (depth) value from 0.0 to 1.0.

GL_FOG_MODE
The fog type; specifies the formula used to render fog effects
(GL_LINEAR, GL_EXP, or GL_EXP2).

GL_FOG_START
The closest distance to which fog is applied. This is a
transformed Z (depth) value from 0.0 to 1.0.




param
GLfloat, GLint: The parameter value.
params
GLfloat *, GLint *: A pointer to the parameter array.
Returns
None.
Example
See the example in CH16\FOGSCENE.C on the CD.
































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