There is a reference: "Mais attention sur une même ligne horizontale on ne peut mettre au maximum that 4 sprites et sur tout l'écran 32, à moins que j'ai mal lut datasheet.
", which I think is wrong.
in sc4-sc8 modes (12 in 2+), the limit of sprites is 8 in line (32 on screen) with one color per line.
I think he's probably talking about 3-color/line sprites (using OR colors), since the 1-color/line sprites are useful mostly for bullets. Then the limit falls back to 4 sprites/line again.
