first texlod is load into slot number in the graphics card level of detail meens
dds TEXTUREMAP mid mapping i do not know if openglES can handle this that why i gave you the link so it works and it is an opengles shader download shadertoy app and see for your android,ipad,iphone it is webgl 2.0
there is nothing wrong with your code , but is is directx microsoft version of opengl
opengl is iso standdard not directx
iso standard says it works on all devices theat run opengles 2.0
texlod samples the vertex data from a texturemap so it has to be grayscale for height stored i alpha buffer and rgb is the normal map in the texture i hope you have done that
you sample .r buffers for the lod use the .a(depth)
when you have done that draw a quad to the screen with the shader and project it to the screen
with this code taken from the link
vec2 p = (2.0 * fragCoord.xy - iResolution.xy) / iResolution.y;
then you have the sample p=point on screen
it is simlier to this o.Position = mul(i.Position, WVP)
your code iResolution is your rendertarget output and a simple quad in screen space
have look at manny samples at shadertoy and write your shader in opengl
write again if you do understand i see if i can help you
Michael