HP Workstation zx2000 OpenGL 1.1 Reference for HP-UX 11.x - Page 34

B glBlendFunc Table 2-1 Parameters Parameter GL_ZERO GL_ONE GL_SRC_COLOR GL_ONE_MINUS_SRC_COLOR GL_DST_COLOR GL_ONE_MINUS_DST_COLOR GL_SRC_ALPHA GL_ONE_MINUS_SRC_ALPHA GL_DST_ALPHA GL_ONE_MINUS_DST_ALPHA GL_SRC_ALPHA_SATURATE (fR, fG, fB, fA) (0, 0, 0, 0) (1, 1, 1, 1) (Rs/kR, Gs/kG, Bs/kB, As/kA) (1,1,1,1) - (Rs/kR, Gs/kG, Bs/kB, As/kA) (Rd/kR, Gd/kG, Bd/kB, Ad/kA) (1, 1, 1, 1) - (Rd/kR, Gd/kG, Bd/kB, Ad/kA) (As/kA, As/kA, As/kA, As/kA) (1, 1, 1, 1) - (As/kA, As/kA, As/kA, As/kA) (Ad/kA, Ad/kA,Ad/kA,Ad/kA) (1, 1, 1, 1) - (Ad/kA, Ad/kA,Ad/kA,Ad/kA) (i, i, i,1) In the table, i = min(As, kA - Ad) / kA To determine the blended RGBA values of a pixel when drawing in RGBA mode, the system uses the following equations: Rd = min(kR, Rs sR + Rd dR) Gd = min(kG, Gs sG + Gd dG) Bd = min(kB, Bs sB + Bd dB) Ad = min(kA, As sA + Ad dA) Despite the apparent precision of the above equations, blending arithmetic is not exactly specified, because blending operates with imprecise integer color values. However, a blend factor that should be equal to 1 is guaranteed not to modify its multiplicand, and a blend factor equal to 0 reduces its multiplicand to 0. For example, when sfactor is GL_SRC_ALPHA, dfactor is GL_ONE_MINUS_SRC_ALPHA, and As is equal to kA, the equations reduce to simple replacement: Rd = Rs Gd = Gs Bd = Bs Ad = As 34 Chapter 2