See:
I very need to resolve this problem, if you have suggestion do not hesitate.
2D simple Shader reflection
Okay, is there a workaround?
I need it to reflect the entire area regardless of the y of the camera
backbuffercopy can help ?
From the reflection area, depends on the shader with scale_y which copies the image at the top
imagine a player or a physical element being part of the effect, that would be better...
BackBufferCopy can copy either the entire screen or a region. If set to only a region (not the whole screen) and your shader uses pixels not in the region copied, the result of that read is undefined (most likely garbage from previous frames). In other words, it's possible to use BackBufferCopy to copy back a region of the screen and then read the screen texture from a different region.
mistouluf Not sure I understand what you mean. BackBufferCopy can still only access what's visible on the screen. You can't get pixels that were not rendered. If you need that, your best option is to setup a custom viewport and adjust its camera to render the complete area that's needed for the reflection and then read that viewport's framebuffer texture in the shader. In order for this to work, you'll have to calculate viewport's camera position depending of how much of the "water" is visible so it "sees" all the stuff that's not visible on the main screen but still visible in the reflection.
I don't understand, how to recover the texture of the viewport outside the camera?