Clear Rect in Render Texture

Hi!

I'm using pixi 4.5.3 and can't find a way to clear out an rectangle from my transparent render texture. Seems that all blend modes have gl.ONE_MINUS_SRC_ALPHA in them 

Is there any hack around this?

I have a large renderTexture with mostly static bitmap text and I want to update only parts that have changed for better performance. Is there any other way to update only part of an rendertexture while retaining transparency?

Thanks!