How to access the alpha channel for texture lookup?

[colac]

Hi,
Could someone tell me how to use the alpha channel for texture loopup?
For example, in my program, I use the description to load texture file =>
<texture name= "rockwall_normal_tex" filename="textures/collage/collage_step.png" pixel_format="RGBA_32F" filtering_mode="NONE"/>
And in shader program, I use =>
vec4 t=texture2D(heightMap, texCoord.xy);

But I can't read anything in t.a or t.w.

Do I miss anything about it?
Hope someone could help me, thx.

colac

[JeGX]

Hello,

floating point textures behave differently if you have an ati or nvidia cg.
With nVidia gpus, you have to use texture rectangle to init floating point buffer. You can init this kind of texture like this with Hyperion:

Code: [Select]


<texture type="TEXTURE_RECTANGLE_2D" pixel_format="RGBA_32F" >
...
</texture>


On ati's board, your code should run. Maybe, try to use power of two texture.
Keep us informed!

[colac]

Thanks for your words.
I just use general texture image such as *.tga, and I don't know how to define its pixel_format such that I can use the alpha channel.
For example, I use pixel_format="RGB" to access the rgb channel. It's OK.
But now I want to access alpha channel for a normal 32bits texture that each channel forms a byte. My problem is how should I define the pixel_format, is it pixel_format = "RGBA"? I try to use some combinations but in vain... Sorry I don't find the document which describes how to define it. thx

colac

[colac]

Hello,

floating point textures behave differently if you have an ati or nvidia cg.
With nVidia gpus, you have to use texture rectangle to init floating point buffer. You can init this kind of texture like this with Hyperion:

Code: [Select]


<texture type="TEXTURE_RECTANGLE_2D" pixel_format="RGBA_32F" >
...
</texture>


On ati's board, your code should run. Maybe, try to use power of two texture.
Keep us informed!

I could simply reads the data from t.r or t.g or t.b, but I can't read t.a/t.w.

colac

[JeGX]

I added a new code sample that shows how to access to the alpha channel in the pixel shader to perform alpha testing:
Code Sample 112

The thing to know is that hyperion does not read the alpha channel of a tga texture. So you have to provide the base and the alpha maps separately and combine them with hyperion.

[colac]

I added a new code sample that shows how to access to the alpha channel in the pixel shader to perform alpha testing:
Code Sample 112

The thing to know is that hyperion does not read the alpha channel of a tga texture. So you have to provide the base and the alpha maps separately and combine them with hyperion.

Hi,
The link seems fail.
I got the message => Unknown ERROR - Please Try Again...
thx

colac

[JeGX]

It's fixed now!