openGL and JOGL

Blending Function

glBlendFunc() Controls how color values in the fragment being processed (the source) are combined with those already stored in the framebuffer (the destination).
You use glBlendFunc() to supply two constants: one that specifies how the source factor should be computed, and one that indicates how the destination factor should be computed.

void glBlendFunc(GLenum sfactor, GLenum dfactor)

The argument sfactor indicates how to compute a source blending factor; dfactor indicates how to compute a destination blending factor. The possible values for these arguments are explained in the Table.

In the Table, the RGBA values of the source and destination are indicated with the subscripts s and d, respectively. Also, division of an RGBA quadruplet by a scalar means dividing each component by that value. Similarly, subtraction of quadruplets means subtracting them componentwise. The Relevant Factor column indicates whether the corresponding constant can be used to specify the source or destination blend factor.

Blending factors of RGB and A can be considered separately:

void glBlendFuncSeparate(GLenum srcRGB, GLenum destRGB, GLenum srcalpha, GLenum destalpha );
It still usees the table below.

Source and Destination Blending Factors
Constant Relevant Factor Computed Blend Factor

GL_ZERO source or destination (0, 0, 0, 0)

GL_ONE source or destination (1, 1, 1, 1)

GL_DST_COLOR source (Rd, Gd, Bd, Ad)

GL_SRC_COLOR destination (Rs, Gs, Bs, As)

GL_ONE_MINUS_DST_COLOR source (1, 1, 1, 1)-(Rd, Gd, Bd, Ad)

GL_ONE_MINUS_SRC_COLOR destination (1, 1, 1, 1)-(Rs, Gs, Bs, As)

GL_SRC_ALPHA source or destination (As, As, As, As)

GL_ONE_MINUS_SRC_ALPH A source or destination (1, 1, 1, 1)-(As, As, As, As)

GL_DST_ALPHA source or destination (Ad, Ad, Ad, Ad)

GL_ONE_MINUS_DST_ALPH A source or destination (1, 1, 1, 1)-(Ad, Ad, Ad, Ad)

GL_SRC_ALPHA_SATURATE source (f, f, f, 1); f=min(As, 1-Ad)

GL_CONSTANT_COLOR source or destination (Rc, Gc, Bc, Ac)

GL_ONE_MINUS_CONSTANT_COLOR source or destination (1, 1, 1, 1)-(Rc, Gc, Bc, Ac)

GL_CONSTANT_ALPHA source or destination (Ac, Ac, Ac, Ac)

GL_ONE_MINUS_CONSTANT_ALPHA source or destination (1, 1, 1, 1)-(Ac, Ac, Ac, Ac)

Source and Destination Blending Factors
Constant	Relevant Factor	Computed Blend Factor
GL_ZERO	source or destination	(0, 0, 0, 0)
GL_ONE	source or destination	(1, 1, 1, 1)
GL_DST_COLOR	source	(Rd, Gd, Bd, Ad)
GL_SRC_COLOR	destination	(Rs, Gs, Bs, As)
GL_ONE_MINUS_DST_COLOR	source	(1, 1, 1, 1)-(Rd, Gd, Bd, Ad)
GL_ONE_MINUS_SRC_COLOR	destination	(1, 1, 1, 1)-(Rs, Gs, Bs, As)
GL_SRC_ALPHA	source or destination	(As, As, As, As)
GL_ONE_MINUS_SRC_ALPH A	source or destination	(1, 1, 1, 1)-(As, As, As, As)
GL_DST_ALPHA	source or destination	(Ad, Ad, Ad, Ad)
GL_ONE_MINUS_DST_ALPH A	source or destination	(1, 1, 1, 1)-(Ad, Ad, Ad, Ad)
GL_SRC_ALPHA_SATURATE	source	(f, f, f, 1); f=min(As, 1-Ad)
GL_CONSTANT_COLOR	source or destination	(Rc, Gc, Bc, Ac)
GL_ONE_MINUS_CONSTANT_COLOR	source or destination	(1, 1, 1, 1)-(Rc, Gc, Bc, Ac)
GL_CONSTANT_ALPHA	source or destination	(Ac, Ac, Ac, Ac)
GL_ONE_MINUS_CONSTANT_ALPHA	source or destination	(1, 1, 1, 1)-(Ac, Ac, Ac, Ac)

The blend factors are assumed to lie in the range [0,1]; after the color values in the source and destination are combined, they're clamped to the range [0,1].

Using the constants GL_ONE (source) and GL_ZERO (destination) gives the same results as when blending is disabled; these values are the default.

If you use the GL*CONSTANT* blending function you need to use glBlendColor() to specify a constant color.

void glBlendColor( GLclamp red, GLclamp green, GLclamp blue, GLclamp alpha )