VkBlendOp

Once the source and destination blend factors have been selected, they along with the source and destination components are passed to the blending operations. RGB and alpha components can use different operations. Possible values of VkBlendOp, specifying the operations, are:

typedef enum VkBlendOp {
    VK_BLEND_OP_ADD = 0,
    VK_BLEND_OP_SUBTRACT = 1,
    VK_BLEND_OP_REVERSE_SUBTRACT = 2,
    VK_BLEND_OP_MIN = 3,
    VK_BLEND_OP_MAX = 4,
} VkBlendOp;

The semantics of the basic blend operations are described in the table below:

Table 1. Basic Blend Operations
VkBlendOp	RGB Components	Alpha Component
VK_BLEND_OP_ADD	R = Rs0 × Sr + Rd × Dr G = Gs0 × Sg + Gd × Dg B = Bs0 × Sb + Bd × Db	A = As0 × Sa + Ad × Da
VK_BLEND_OP_SUBTRACT	R = Rs0 × Sr - Rd × Dr G = Gs0 × Sg - Gd × Dg B = Bs0 × Sb - Bd × Db	A = As0 × Sa - Ad × Da
VK_BLEND_OP_REVERSE_SUBTRACT	R = Rd × Dr - Rs0 × Sr G = Gd × Dg - Gs0 × Sg B = Bd × Db - Bs0 × Sb	A = Ad × Da - As0 × Sa
VK_BLEND_OP_MIN	R = min(Rs0,Rd) G = min(Gs0,Gd) B = min(Bs0,Bd)	A = min(As0,Ad)
VK_BLEND_OP_MAX	R = max(Rs0,Rd) G = max(Gs0,Gd) B = max(Bs0,Bd)	A = max(As0,Ad)

In this table, the following conventions are used:

R_s0, G_s0, B_s0 and A_s0 represent the first source color R, G, B, and A components, respectively.
R_d, G_d, B_d and A_d represent the R, G, B, and A components of the destination color. That is, the color currently in the corresponding color attachment for this fragment/sample.
S_r, S_g, S_b and S_a represent the source blend factor R, G, B, and A components, respectively.
D_r, D_g, D_b and D_a represent the destination blend factor R, G, B, and A components, respectively.

The blending operation produces a new set of values R, G, B and A, which are written to the framebuffer attachment. If blending is not enabled for this attachment, then R, G, B and A are assigned R_s0, G_s0, B_s0 and A_s0, respectively.

If the color attachment is fixed-point, the components of the source and destination values and blend factors are each clamped to [0,1] or [-1,1] respectively for an unsigned normalized or signed normalized color attachment prior to evaluating the blend operations. If the color attachment is floating-point, no clamping occurs.