// This function mixes two bytes According to value of TRANS
// The value of TRANS is between 0 (result then will be equal to FG)
// and 255 (result then will be equal to BG)
function MixBytes(FG, BG, TRANS: byte): byte;
asm
push bx // push some regs
push cx
push dx
mov DH,TRANS // remembering Transparency value (or Opacity - as you like)
mov BL,FG // filling registers with our values
mov AL,DH // BL = ForeGround (FG)
mov CL,BG // CL = BackGround (BG)
xor AH,AH // Clear High-order parts of regs
xor BH,BH
xor CH,CH
mul BL // AL=AL*BL
mov BX,AX // BX=AX
xor AH,AH
mov AL,DH
xor AL,$FF // AX=(255-TRANS)
mul CL // AL=AL*CL
add AX,BX // AX=AX+BX
shr AX,8 // Fine! Here we have mixed value in AL
pop dx // Hm... No rubbish after us, ok?
pop cx
pop bx // Bye, dear Assembler - we go home to Delphi!
end;
// Here we mix R,G and B channels of our colors separately.
// The value of T is between 0 and 255 as described above.
// As you know, TColor value is 4 bytes length integer value where
// low byte is red channel, 2nd byte is green and 3rd byte is blue
function MixColors(FG, BG: TColor; T: byte): TColor;
var r,g,b:byte;
begin
R := MixBytes(FG and 255,BG and 255,T); // extracting and mixing Red
G := MixBytes((FG shr 8) and 255,(BG shr 8) and 255,T); // the same with green
B := MixBytes((FG shr 16) and 255,(BG shr 16) and 255,T); // and blue, of course
Result := r+g*256+b*65536; // finishing with combining all channels together
end;
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