Textures containing transparent sections

Blitz3D Forums/Blitz3D Programming/Textures containing transparent sections

Glitch01

(Posted 2003) [#1]

I am having some trouble creating a texture with transparency from a masked image in memory.

Here's what I'm trying to do... my program generates an image in memory with certain parts having RGB values of 255,0,255 which I then set as masked. If I draw this to the screen as a normal image it will plot correctly with the 255,0,255 portions invisible.

Now I need to create a texture out of this image, maintaining transparency where the color is 255,0,255. I can't seem to get this to work.

I create the texture, set the buffer to texturebuffer() of my texture and DrawImage() the image to the texture. If I apply this texture to an object using the COLOR flag, it draws the texture showing the 255,0,255 color.. if I try to set the MASKED flag it draws the entire texture completely black.

I've tried setting different texture flags but nothing is working as I imagined (they either turn the texture completely black on the screen or completely invisible). I tried searching the forums and wasn't able to find any threads on this (if they exist I sure couldn't find them!).

Any help would be greatly appreciated :-)

-Steve

Ross C

(Posted 2003) [#2]

i'm not sure if you can set the masked colour of a texture. I'd be very glad if someone proved me wrong tho :) Oh the search feature of the forums kinda sucks, so don't give up if you've searched and not came across anything :o)

Could you not just set use 0,0,0 as your masked colour? And set the black parts to 1,1,1?

Glitch01

(Posted 2003) [#3]

Not sure I understand what you mean by setting the black to 1,1,1 ...

Here's a very stripped down example of what I'm trying to do.. I'd like the black part of the texture (the black circle) to be transparent or even semi-transparent:

[CODE]

Graphics3D 640,480,0,2

camera = CreateCamera()
light = CreateLight()
cube = CreateCube()
sphere = CreateSphere()

;Create image
gfx = CreateImage(64,64)
SetBuffer ImageBuffer(gfx)
ClsColor 200,0,0
Cls()
Color 0,0,0
Oval 2,2,60,60,True
Color 255,255,255
Text 10,25,"HELLO!"
MaskImage gfx,0,0,0

;Create texture from masked image
tex = CreateTexture(64,64,1)
SetBuffer TextureBuffer(tex)
DrawImage gfx,0,0

SetBuffer BackBuffer()

;Apply texture to cube
EntityTexture cube, tex

;Position Camera
PositionEntity camera,0,-5,0
PointEntity camera,cube

While Not KeyHit(1)
TurnEntity cube,1,2,1
UpdateWorld()
RenderWorld()
Flip()
Wend
End
[/CODE]

-Steve

jfk EO-11110

(Posted 2003) [#4]

First - there are two Transparency Modes for Textures: Mask and Alpha.

You have to define this as the Textureflag, 4 for Mask or 2 for Alpha.

tex=createtexture(64,64,2 or 1)
so it's Alpha as well as fullright.

With Mask you only have the choice of opaque(non-black) or fully transparent(black). With alpha the Brightness of the Pixel will define its tranparency, the darker, the more transparent, UNLESS you load a Texture with a predefined Alpha-Channel such as a 32 Bit TGA Picture.

However, you can manipulate the Alpha-Channel of a Texture in Memory whenever you like this way:

setbuffer texturebuffer(tex)
lockbuffer
for j=0 to textureheight(tex)-1
 for i=0 to texturewidth(tex)-1
  rgb=readpixelfast(i,j) and $FFFFFF
  ;  example of semitransparence for black parts:
  if rgb=0 ; black
   argb=(127 shl 24) or rgb ; using 127 for alphabyte
  else
   argb=rgb ; alphabyte remains zero
  endif
  writepixelfast i,j,argb
 next
next
unlockbuffer
setbuffer backbuffer()

Please note, that unlike Maskmode the Alphamode sometimes makes Problems with the Z-Order of the Objects, especially if they have intersecting parts.

Glitch01

(Posted 2003) [#5]

JFK:

Thanks for your reply, this is essentially what I was after, only I hoped there was an "easier" way to do this using drawimage() or copyrect().

Not long before you posted I found another thread that gave a very similar solution to what you gave here.

I did notice a z-order flaw when using the alpha (and later read a reference to this in a different thread). Too bad as I was looking forward to using alpha rather than a complete mask. Is there any work-around for this?

Thanks again for your help!

-Steve