[Rubygame]Making transparent surfaces

[ZenVirZan]

I'm developing a map editing application, and all is going well, except for blitting transparent surfaces from scratch to the screen.
If i blit a .png with transparency, it merges them fine - the sprite on the background.
But if I blit a surface (Surface.new([width;height])), it leaves a black box, rather than the transparency.

How to I get the alpha channels to merge correctly from Surfaces made from scratch?

 

[Xilef]

You need to use surface to_display_alpha after creating the surface with surface::new

 

[ZenVirZan]

Even when using #to_display_alpha, the issue still persists, with and without the SRCALPHA flag.

 

[Xilef]

Want to post some of your code?

 

[ZenVirZan]

This is from a different project, but the issue is the same.
The reason I was sending the text to another surface was to apply an outline - I've removed the outline code for now.
Pretty much:

  def draw_text(font,string,color)

    size = @font[font].size_text(string)

    text2 = @font[font].render(string,true,color)

    surface = Surface.new [text2.w,text2.h],0,[HWSURFACE,SRCALPHA]

    surface.to_display_alpha

    text2.blit(surface,[0,0])

    return surface

  end

 

# other stuff . .  .

    @text  = []

    @text[0] = draw_text('ubuntu,16','Armour',[255,255,255])

    @text_rect = []

    @text_rect[0] = Rect.new(16,20,@text[0].make_rect.w,@text[0].make_rect.h)

 

#moar stuff . . .

 

    @text[0].blit($screen,@text_rect[0]) # within the draw method

 

 

[Xilef]

You need to assign a surface to surface.to_display_alpha and blit that, you should be able to write:
surface = surface.to_display_alpha
and it should work, the reason is that it's not a self-modifying function it has a return value of a new surface.

 

[ZenVirZan]

Its merging now, thank you :D
Its a pity they don't make it more noticeable in the documentation - It's such a simple mistake.

 

[Xilef]

Its merging now, thank you :D
Its a pity they don't make it more noticeable in the documentation - It's such a simple mistake.

And now this is when I shock you by revealing I've never coded in Ruby before and that I've never used RubyGame before.

 

[ZenVirZan]

Its merging now, thank you :D
Its a pity they don't make it more noticeable in the documentation - It's such a simple mistake.

And now this is when I shock you by revealing I've never coded in Ruby before and that I've never used RubyGame before.

Oh wow. :blank:
I am shocked D:

EDIT: New issue.
3 surfaces.
a = Loaded from png with transparency
b = Scratch (has been converted)
c = Scratch (has been converted)
Blitting surfaces a => screen, b => screen and c => screen works
Blitting surfaces a => b => screen and a => c => screen works
But blitting a => b => c => screen doesnt.
If two surfaces have to_display_alpha set, it doesn't show the PNG image blitted onto it.

 

[ZenVirZan]

:snip:
Double posted for some reason

 

[Xilef]

3 surfaces.
a = Loaded from png with transparency
b = Scratch (has been converted)
c = Scratch (has been converted)
Blitting surfaces a => screen, b => screen and c => screen works
Blitting surfaces a => b => screen and a => c => screen works
But blitting a => b => c => screen doesnt.
If two surfaces have to_display_alpha set, it doesn't show the PNG image blitted onto it.

Could you tell me the dimensions of these surfaces and the screen you're blitting to?

 

[ZenVirZan]

surface 'a' is the tileset png file, alpha included.
surface 'b' is a 32x32 tile, blitted to from the tileset image.
surface 'c' is a 1024x800 layer, and has the surface 'a's blitted to it to make the map. (#to_display_alpha is applied)
'screen' is a 1280x800 Screen instance.

If I put #to_display_alpha on surface b, it doesn't show up.
If I omit it, it does show, but the alpha is replaced with black.

 

[Xilef]

Why are you using surface B at all? You should use clipping to blit a 32x32 section of A straight to C and do any modifications there to save processing speed.
You can do that with the third blit parameter which is a rectangle, instead of having only the x and y position you can add in the width and height of the blit, using surfaces to clip is very inefficient as you're copying entire blocks of ram to a fresh set of memory twice.

$a.blit($c,[destinationX,destinationY],[tileX,tileY,32,32])

 

[ZenVirZan]

I have a grid class, which has a method #get_tile(id)
It returns a 32x32 tile surface from the tileset, depending on the id.
It already uses the source rect function of #blit to get the tile onto surface b to begin with.
Even though b may not be required, i'd still like to know for future reference.

 

[Xilef]

I don't think I can help any further then, I generally don't blit through more than two surfaces, it's probably a problem with preserving the alpha channel (Perhaps it's being overwritten when blitting from B to C?), it would be a Rubygame specific bug (And from looking at the git page, it's full of them)

 

[ZenVirZan]

I managed to fix it somehow.
I removed the SRCALPHA flag from the loaded tileset .png and it works now.
Thanks for your help, Xilef

 

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