Declaration

function MergeReg(F, B: TColor32): TColor32;
procedure MergeMem(F: TColor32; var B: TColor32);
procedure MergeMems(F: TColor32; Dst: PColor32; Count: Integer);
function MergeRegEx(F, B: TColor32; M: Cardinal): TColor32;
procedure MergeMemEx(F: TColor32; var B: TColor32; M: Cardinal);
procedure MergeLine(Src, Dst: PColor32; Count: Integer);
procedure MergeLineEx(Src, Dst: PColor32; Count: Integer; M: Cardinal);

Parameters

Parameter	Type	Description
F	TColor32	Foreground pixel color.
B	TColor32	Background pixel color.
M	Cardinal	Master alpha weight or mask value (0..255).
Src	PColor32	Pointer to the first source foreground pixel in memory.
Dst	PColor32	Pointer to the first destination background pixel in memory.
Count	Integer	Number of contiguous background pixels to blend.

Returns

Type	Description
TColor32	The blended 32-bit ARGB result color.

Description

The Merge* family of functions performs associative alpha merging based on Bruce Wallace's 1981 compositing formulation:

$$R_a=F_a+B_a\cdot (1-F_a)$$$$R_c=B_c+\frac{F_a}{R_a}\cdot (F_c-B_c)$$

Unlike standard alpha blending (Blend), Merge handles semi-transparent background colors accurately, maintaining associativity:

$$(A\text{ over }B)\text{ over }C=A\text{ over }(B\text{ over }C)$$

Variant Summary

Variant	Signature	Description
MergeReg	function(F, B: TColor32): TColor32;	Merges foreground $F$ and background $B$ in registers.
MergeMem	procedure(F: TColor32; var B: TColor32);	Merges foreground $F$ directly into memory location $B$.
MergeMems	procedure(F: TColor32; B: PColor32; Count: Integer);	Merges uniform foreground $F$ into Count background pixels starting at $B$.
MergeRegEx	function(F, B: TColor32; M: Cardinal): TColor32;	Register merging with master alpha / mask factor $M$ ($0\dots 255$).
MergeMemEx	procedure(F: TColor32; var B: TColor32; M: Cardinal);	In-memory merging with master alpha / mask factor $M$ ($0\dots 255$).
MergeLine	procedure(Src, Dst: PColor32; Count: Integer);	Scanline merging of Count source pixels onto destination pixels.
MergeLineEx	procedure(Src, Dst: PColor32; Count: Integer; M: Cardinal);	Scanline merging with master alpha factor $M$.

INFO

All these functions are actually delegates; At startup, Graphics32 binds them to the optimal implementation (Pure Pascal, x86/x64 assembly, or SSE2 vector instructions) supported by the host CPU.

See also

• Blend
• Combine
• Alpha Composition
• Naming Conventions