AGS 4: Remove "has alpha channel" flag from sprites, and drawable objects

[ivan-mogilko]

In AGS sprites have a "has alpha channel" flag which tells whether the image's alpha channel should be used or not. Certain drawing operations depend on it; for instance a blending op or conversion from the sprite to texture may be performed in one or another way depending on the combination of source and destination surfaces' alpha flags.

My proposal is to remove this flag and those checks altogether, and imply that 32-bit images always have a valid alpha channel. This should somewhat simplify all the drawing operations.

If necessary, the flag may remain in sprite import settings; in such case removal of an alpha channel from a 32-bit source image would correspond to filling alpha bytes with 0xff (fully opaque).

[ericoporto]

Hey, does this need some form of project upgrade to work, when loading an existing project, or nothing is necessary to change in the project part?

[ivan-mogilko]

Hey, does this need some form of project upgrade to work, when loading an existing project, or nothing is necessary to change in the project part?

Possibly it might have to reimport 32-bit sprites "without alpha channel"; but I haven't double checked if that's necessary yet.

[ivan-mogilko]

The consequences of this would be that the 32-bit images with "magic pink" color would have to be converted on import or load from custom files at runtime (right now this is done when converting to texture).

Actually, current behavior with "magic pink" had to be kept, because it's the only way to set transparent color in DrawingSurface even in 32-bit games. We'd need a proper 32-bit color value support in game data & script before we may get rid of it (see #1980)

[ivan-mogilko]

Resolved by #1813