Changes

A proper isometric render always need to get masked sprites so they may appear upon the backgroundor behind other elements.

Also some Scenery Elements which are to be put in front of sprites also have to be masked.

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The following was certainly the best one, it is probably the technique used in '''Head Over Heels''' was certainly the best one :

***Background : can be in 4 colours, it is used for the floor, HUD and backgrounds walls only. You can use a set of 2D tiles with no mask and those can never be "foreground"***Sprites and fore-ground elements (objects, doors, platforms...) : they use only 3 colours and the 4th ink is used to get the mask.

'''Hero Quest''' per example is quite similar***The doors actually manage to fit well in the background.

The floor-tiles ***Sprites and background walls are masked, the "4th colour" Scenery elements (greyobjects, actually ink0doors, platforms...) : they use only 3 colours and the 4th ink is nearly never used except for to get the "empty floor" or the "Mouse cursor"..mask.

'''Hero Quest''' is quite similar yet fail to achieve this level of goodness. The floor-tiles and background walls are masked, the "4th colour" (grey, actually ink0) is nearly never used inside those except for the "empty floor" or the "Mouse cursor"...  A more clever use of the transparency/mask ink with the Floor/Wall tiles could enable to display this '''background grey''' in those floor/wall tiles but it wasn't done... which is a serious graphical limitation alongside a poor colours choice, which leads to the sprites and scenery being quite blurred into a blue messy hell as the background can't differenciate properly through the use of an additional different colour. It is also to notice that the some basic floor tiles use only 2 inks +transparency (Blue and dark blue) the "light cyan" seen in the jointed floor-tiles being sometimes then obtained with by the pixels-crossing of pixels from 2 tiles differentFloor-tiles.