I need to flip my texture vertically when copying it into another texture.I know about 3 simple ways to do it:
1 . Blit from once FBO into another using full screen quad (and flip in frag shader)
2 . Blit using glBlitFrameBuffer.
3 . Using glCopyImageSubData
I need to perform this copy between 2 textures which aren't attached to any FBO so I am trying to avoid first 2 solutions.I am trying the third one.
Doing it like this:
glCopyImageSubData(srcTex ,GL_TEXTURE_2D,0,0,0,0,targetTex,GL_TEXTURE_2D,0,0,width ,0,height,0,1);

It doesn't work.The copy returns garbage.Is this method supposed to be able to flip when reading?Is there an alternative FBO unrelated method(GPU side only)?
Btw:
glCopyTexSubImage2D(GL_TEXTURE_2D,0,0,0,0,height ,width,0 );

Doesn't work too.

https://stackoverflow.com/questions/19564657/flipping-texture-when-copying-to-another-texture