public void setReflectionMapSize(int reflectionMapSize) {
        this.reflectionMapSize = reflectionMapSize;
        //if reflection pass is already initialized we must update it
        if(reflectionPass !=  null){
            reflectionPass.init(renderManager.getRenderer(), reflectionMapSize, reflectionMapSize, Format.RGBA8, Format.Depth);
            reflectionCam.resize(reflectionMapSize, reflectionMapSize, true);
            reflectionProcessor.setReflectionBuffer(reflectionPass.getRenderFrameBuffer());
            material.setTexture("ReflectionMap", reflectionPass.getRenderedTexture());
        }

    }
Sets the size of the reflection map
default is 512, the higher, the better quality, but the slower the effect.

@param reflectionMapSize the desired size (in pixels per side,
default=512)
jme3-effects/src/main/java/com/jme3/water/WaterFilter.java