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.


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.


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)

  • \$\begingroup\$ With this method, i think the image will not keep their native resolution and the transparency will be lost. So it will not help me but it's a good approach i think, i'll try something like that \$\endgroup\$ – Sata Jan 14 '15 at 9:45
  • 2
    \$\begingroup\$ I added more information on how to achieve this with render textures. You will be able to keep the images native resolution and the transparency. \$\endgroup\$ – Stephane Hockenhull Jan 14 '15 at 15:41
  • \$\begingroup\$ I find a very helpfull code sample about doing this with RenderTexture here : link Thanks for helping me to find the right way do to it. \$\endgroup\$ – Sata Jan 16 '15 at 16:09
  • \$\begingroup\$ I meet with some graphic glitch in trying to use renderTexture on mac (link), i have already try to change the camera clear flags but it didn't work. So if you have any tips \$\endgroup\$ – Sata Jan 28 '15 at 8:27
  • \$\begingroup\$ Found solution using GL.Clear() to remove glitch. \$\endgroup\$ – Sata Jan 29 '15 at 14:30

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