How can I merge multiple sprite into one sprite or texture using Unity3d?

Question

I have an avatar generator where someone can create a custom avatar with layers superimposed. And in order to reuse this image multiple times, i want to merge all layers in one image. Is there any way on unity3D to create this image.

I've already coded that :

atlas = new Texture2D (width, height, TextureFormat.RGBA32, false);
foreach (Sprite s in allSprite) {
        atlas.SetPixels (0, 0, atlas.width, atlas.height, s.texture.GetPixels (0, 0, atlas.width, atlas.height));
        atlas.Apply ();
}

My problem is to keep the transparency and not erase old layers where pixels are transparent. The setPixels method replace old pixels in atlas by new one. I can't loop over pixels because of the size of the image (1024*1024) and more than 6 layers.

Answer 1

You can use a RTT (render-to-texture) and a custom camera to one-shot render to it to merge all the layers using the GPU.

You can then save and use the resulting texture.

http://docs.unity3d.com/Manual/class-RenderTexture.html

If your render texture has alpha then it will maintain the composited alpha values as long as you use the proper separate color-alpha blending mode in the shaders:

Blend SrcAlpha OneMinusSrcAlpha, OneMinusDstAlpha One

If you only need full-size texture blending you can use graphic blit commands to get pixel-aligned full-texture blend (http://docs.unity3d.com/ScriptReference/Graphics.Blit.html)

Otherwise you'll need to draw pixel-aligned (http://docs.unity3d.com/ScriptReference/GL.LoadPixelMatrix.html) quads using the GL namespace functions (http://docs.unity3d.com/ScriptReference/GL.html)