Declaration

function CombineReg(F, B: TColor32): TColor32;
procedure CombineMem(F: TColor32; var B: TColor32);
procedure CombineLine(Src, Dst: PColor32; Count: Integer);

Parameters

Parameter	Type	Description
F	TColor32	Foreground pixel color.
B	TColor32	Background pixel color.
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 Combine* family of functions performs linear interpolation (Lerp) between two 32-bit ARGB colors ($X$ and $Y$) given weight $W\in [0,255]$:

$$Z=\frac{W}{255}\cdot X+(1-\frac{W}{255})\cdot Y=\frac{W\cdot (X-Y)}{255}+Y$$

All four channels (Alpha, Red, Green, Blue) are combined simultaneously.

Variant Summary

Variant	Signature	Description
CombineReg	function(X, Y: TColor32; W: Cardinal): TColor32;	Combines colors $X$ and $Y$ in registers with weight $W$.
CombineMem	procedure(X: TColor32; var Y: TColor32; W: Cardinal);	Combines color $X$ into memory location $Y$ in-place with weight $W$.
CombineLine	procedure(Src, Dst: PColor32; Count: Integer; W: Cardinal);	Combines Count pixels between Src and Dst scanline buffers with weight $W$.

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

• BlendReg
• MergeReg
• Alpha Composition
• Naming Conventions