Transparent background

[tolkien]

Hello mates.

I load all my gfx using Datatypes and can blit them using BltBitmapRasport() without problems.
The question is that I need some gfx have the background transparent. I guess I need the mask version of BltBitmapRasport() but I´m unable to show it correctly.
Tried with different minterms but never get any transparency.

I need ideas or know if this is the right function. Hope I have explained it more or less and thanks!

[Mrs Beanbag]

you need to create a mask (by ORing all the bitplanes together) and then use BltMaskBitmapRastPort().

[tolkien]

I have created 1bit mask and use that function. Perhaps I have created a wrong mask? Didn't know about ORing all planes. That is setting bit that want to be displayed to 1 and 0 for transprent. Will try tomorrow again.
And what about the minterm? Thanks.

[thomas]

The correct minterm for blit though mask is ABC|ABNC|ANBC.

You can ask for PDTA_MaskPlane to get a mask from datatypes if the datatype class supports it (and if the image contains a mask plane or a transparent color).

In any case you have to be careful if your display is on the native chipset. If both source and target bitmaps are interleaved, the mask has to be extended vertically to match height * depth, i.e. each row in the mask has to be repeated depth times.

[tolkien]

Good tips thomas. I'll try to get the mask through pdta_maskplane.
Have I to make a bitmap friend?

Thanks mate.

[thomas]

Originally Posted by tolkien

Have I to make a bitmap friend?

Well, it depends.

I am just now developing a project with blit through mask and my experience is that it is very difficult to support all kinds of environments.

Currently my knowledge is like this:

- if you are running native with planar bitmaps, you should not use a friend. Then your source bitmap most likely is not interleaved and thus you can use a simple single-plane mask

- if you are running native and use a friend, then you have to consider interleaved bitmaps and change your mask accordingly.

(interleaved bitmaps are better in speed and have less artifacts, so if you are doing an animation or a moving object, you should go the interleaved route.)

- if you are running RTG with depth <= 8 it does not matter, a single-plane mask is always fine.

- if you are running RTG with depth > 8 you need a friend, because at least CyberGraphics does not blit through a mask if the pixel formats do not match. Picasso96 is more tolerant in many areas, but not here I think. Results are just different: CGX does not blit at all, P96 blits all black but with correct shape.

[tolkien]

Thanks Thomas for all info. I´m rewriting a few things and will try again.