GUI.DrawTexture to draw a rendertexture with particle shaders in the scene.

On runtime :

  -I create a rendertexture with depth of 24 and ARGB32, 
  -then I assign it to the camera.
  -use drawtexture with blend = true to render the rendertexture of the camera.

in the scene I have objects with default shader, and particles like fire and smoke.

the issue is, particles (fire and smoke) are only rendered inside the boundary of the objects with default shader, if the smoke goes higher where the background is no longer any object with default shader, the smoke is not rendered.

Thank you in advance.