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Blending Source and Destination

During blending, color values of the incoming fragment (the source) are combined with the color values of the corresponding currently stored pixel (the destination) in a two-stage process.

First, you specify how to compute source and destination factors. These factors are RGBA quadruplets that are multiplied by each component of the R, G, B, and A values in the source and destination, respectively. Then, the corresponding components in the two sets of RGBA quadruplets are added.

To show this mathematically, let the source and destination blending factors be (Sr, Sg, Sb, Sa) and (Dr, Dg, Db, Da), respectively, and the RGBA values of the source and destination be indicated with a subscript of s or d. Then, the final, blended RGBA values are given by

(RsSr+RdDr, GsSg+GdDg, BsSb+BdDb, AsSa+AdDa)

Each component of this quadruplet is eventually clamped to [0,1].