Options for ETC1 with Transparency

Hi guys,

Sprite based game. I'm considering using the following options for texture compression with alpha on Android.

Option 1. Use an Alpha 8 texture. Adds about 1MB per texture. I wrote the following shader:

Code (csharp):

1. half4frag (v2fIN) : COLOR
2. {
3.   float4ret = tex2D(_MainTex, IN.texcoord) * IN.color;
4.   ret.a *= tex2D(_AlphaTex, IN.texcoord).a;
5.   return ret;
6. }

Option 2. Use another ETC1 texture for the alpha. This adds about 0.5MB per texture. The quality seems comparable, using the following shader:

Code (csharp):

1. half4frag (v2fIN) : COLOR
2. {
3.   float4ret = tex2D(_MainTex, IN.texcoord) * IN.color;
4.   ret.a *= tex2D(_AlphaTex, IN.texcoord).g;
5.   return ret;
6. }

(Note I wrote a little script that copies the alpha channel to the g component in the second case.)

Despite the wasted channels, the quality looks very similar in both cases, but in option 2 it looks like we're saving 512k per texture (which is important in our case).

I wonder if anyone has been down this path before and has any thoughts before I dig deeper.....

 

Hi bitter

I've tried this option before but I encountered two problems:

1. I didn't find a way to disable mip maps with it (there might be a workaround)
2. I found the following thread: http://forum.unity3d.com/threads/new-texture-compression-option.353668/

The question I have is: I'm using my own shaders. Where in the render pipeline does Unity combine the two textures it generates? (In other words, is this feature really working?)

Many thanks again

 

Does ETC1/Alpha feature could work for non sprites? I mean for mesh renderer with default type texture

 

It should work for mesh renderer. But it is much easier to drop OpenGL ES 2.0 and use ETC2.