hello
I've seen your message on the pd list about alpha mix of live input
I'had got the same problem as you with the pix_mix box (vertical flip)
It seems that gem prefers working in 3D than with pix_ objects ...
so I've made this box to mix two sources (the mix is in 3D however, it's not recordable with pix_record, but it's viewable)
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#N canvas 122 21 618 206 12; #N canvas 73 182 1032 463 melangeur_3D 0; #X obj 88 346 rectangle 5 4; #X obj 78 -9 inlet; #X msg 323 71 quality $1; #X obj 323 52 tgl 15 0 empty empty empty 0 -6 0 8 -262144 -1 -1 1 1 ; #X obj 90 229 pix_texture; #X obj 90 251 alpha; #X obj 179 158 pix_coloralpha; #X obj 78 187 pix_takealpha; #X obj 180 134 pix_levels; #X msg 197 99 $1 1 1 0; #X floatatom 193 30 5 0 0 0 - - -; #X floatatom 193 76 5 0 0 0 - - -; #X obj 192 53 / 100; #X obj 244 -12 loadbang; #X msg 324 31 1; #X obj 470 343 rectangle 5 4; #X obj 472 -10 inlet; #X obj 472 226 pix_texture; #X obj 477 250 alpha; #X obj 571 168 pix_coloralpha; #X obj 472 196 pix_takealpha; #X obj 572 144 pix_levels; #X floatatom 575 27 5 0 0 0 - - -; #X floatatom 575 73 5 0 0 0 - - -; #X obj 574 50 / 100; #X msg 527 28 69; #X msg 145 31 80; #X obj 640 -58 inlet; #X obj 827 104 pack f f f f; #X floatatom 778 25 5 0 0 0 - - -; #X floatatom 778 64 5 0 0 0 - - -; #X obj 778 43 / 100; #X floatatom 827 24 5 0 0 0 - - -; #X floatatom 825 65 5 0 0 0 - - -; #X obj 824 42 / 100; #X floatatom 875 22 5 0 0 0 - - -; #X floatatom 873 63 5 0 0 0 - - -; #X obj 872 40 / 100; #X floatatom 921 22 5 0 0 0 - - -; #X floatatom 919 63 5 0 0 0 - - -; #X obj 918 40 / 100; #X obj 826 83 t b f; #X obj 873 85 t b f; #X obj 924 86 t b f; #X msg 579 96 0.7 1 $1 0; #X connect 1 0 8 0; #X connect 1 0 7 0; #X connect 2 0 4 0; #X connect 2 0 17 0; #X connect 3 0 2 0; #X connect 4 0 5 0; #X connect 5 0 0 0; #X connect 6 0 7 1; #X connect 7 0 4 0; #X connect 8 0 6 0; #X connect 9 0 8 1; #X connect 10 0 12 0; #X connect 11 0 9 0; #X connect 12 0 11 0; #X connect 13 0 26 0; #X connect 13 0 14 0; #X connect 13 0 25 0; #X connect 14 0 3 0; #X connect 16 0 21 0; #X connect 16 0 20 0; #X connect 17 0 18 0; #X connect 18 0 15 0; #X connect 19 0 20 1; #X connect 20 0 17 0; #X connect 21 0 19 0; #X connect 22 0 24 0; #X connect 23 0 44 0; #X connect 24 0 23 0; #X connect 25 0 22 0; #X connect 26 0 10 0; #X connect 27 0 22 0; #X connect 28 0 21 1; #X connect 29 0 31 0; #X connect 30 0 28 0; #X connect 31 0 30 0; #X connect 32 0 34 0; #X connect 33 0 41 0; #X connect 34 0 33 0; #X connect 35 0 37 0; #X connect 36 0 42 0; #X connect 37 0 36 0; #X connect 38 0 40 0; #X connect 39 0 43 0; #X connect 40 0 39 0; #X connect 41 0 28 0; #X connect 41 1 28 1; #X connect 42 0 28 0; #X connect 42 1 28 2; #X connect 43 0 28 0; #X connect 43 1 28 3; #X connect 44 0 21 1; #X restore 204 88 pd melangeur_3D; #X text 330 59 mix amount (0-100); #X text 244 60 source 2; #X text 150 61 source 1;