Using the Texture Extension

Table 6-1 lists some of the formats defined by the extension; for a complete list, see
the reference page for glTexImage*(). The table shows the token names with their corresponding base formats and their desired component resolutions. It also shows Red (R), Green (G), Blue (B), Luminance (L), Alpha (A), and Intensity (I) values for each format. You can query the actual resolution with glGetTexLevelParameteriv() using
the appropriate token, such as GL_TEXTURE_RED_SIZE_EXT. All OpenGL implementations accept all tokens but may not always allocate a resolution exactly equal to that indicated in the table.

Some Internal Formats Supported by the Texture Extension

Token Name	Base Format	R	G	B	A	L	I
GL_LUMINANCE8_EXT	GL_LUMINANCE					8
GL_LUMINANCE4_ALPHA4_EXT	GL_LUMINANCE_ALPHA				4	4
GL_LUMINANCE12_ALPHA4_EXT	GL_LUMINANCE_ALPHA				4	12
GL_LUMINANCE16_ALPHA16_EXT	GL_LUMINANCE_ALPHA				16	16
GL_INTENSITY8_EXT	GL_INTENSITY_EXT						8
GL_RGB4_EXT	GL_RGB	4	4	4
GL_RGB8_EXT	GL_RGB	8	8	8
GL_RGBA4_EXT	GL_RGBA	4	4	4	4
GL_RGB5_A1_EXT	GL_RGBA	5	5	5	1
GL_RGBA8_EXT	GL_RGBA	8	8	8	8

The extension redefines the application of a texture to the color components of a fragment. In particular, a new texture environment, GL_REPLACE_EXT, and two new texture formats, GL_ALPHA and GL_INTENSITY_EXT, are available. Table 6-2 illustrates this, with the abbreviations having the following meanings:

Rv, Gv, Bv, Av

result of the texture environment function

Rt, Gt, Bt, At

texture color

Rf, Gf, Bf, Af

fragment color

Rc, Gc, Bc, Ac

texture environment color (see GL_TEXTURE_ENV_COLOR)

Texture Functions

Base Texture Format	Replace	Modulate	Blend	Decal
GL_ LUMINANCE	Rv = Lt Gv = Lt Bv = Lt Av = Af	Rv = Rf * Lt Gv = Gf * Lt Bv = Bf * Lt Av = Af	Rv = Rf * (1-Lt) + Rc* Lt Gv = Gf * (1-Lt) + Gc * Lt Bv = Bf * (1-Lt) + Bc * Lt Av = Af	undefined
GL_ALPHA	Rv = Rf Gv = Gf Bv = Gf Av = At	Rv = Rf Gv = Gf Bv = Gf Av = Af * At	Rv = Rf Gv = Gf Bv = Bf Av = Af * At	undefined
GL_ INTENSITY_ EXT	Rv = It Gv = It Bv = It Av = It	Rv = Rf * It Gv = Gf * It Bv = Bf * It Av = Af * It	Rv = Rf * (1-It) + Rc * It Gv = Gf * (1-It) + Gc * It Bv = Bf * (1-It) + Bc * It Av = Af * (1-It) + AcIt	undefined
GL_ LUMINANCE_ALPHA	Rv = Lt Gv = Lt Bv = Lt Av = At	Rv = Rf * Lt Gv = Gf * Lt Bv = Bf * Lt Av = Af * At	Rv = Rf * (1-Lt) + Rc * Lt Gv = Gf * (1-Lt) + Gc * Lt Bv = Bf * (1-Lt) + Bc * Lt Av = Af * At	undefined
GL_RGB	Rv = Rt Gv = Gt Bv = Bt Av = Af	Rv = Rf * Rt Gv = Gf * Gt Bv = Bf * Bt Av = Af	Rv = Rf * (1-Rt) + Rc * Rt Gv = Gf * (1-Gt) + Gc * Gt Bv = Bf * (1-Bt) + Bc * Bt Av = Af	Rv = Rt Gv = Gt Bv = Bt Av = Af
GL_RBGA	Rv = Rt Gv = Gt Bv = Bt Av = At	Rv = Rf * Rt Gv = Gf * Gt Bv = Bf * Bt Av = Af * At	Rv = Rf * (1-Rt) + Rc * Rt Gv = Gf * (1-Gt) + Gc * Gt Bv = Bf * (1-Bt) + Bc * Bt Av = Af * At	Rv = Rf * (1-At) + Rt * At Gv = Gf * (1-At) + Gt * At Bv = Bf * (1-At) + Bt * At Av = Af