Sampler 2D Alpha Value Stays at 1 - glsl

Question

I create a texture for use in a 2D sampler as a displacement map for a mesh of tessellated terrain. Using the passed in vertex coordinates, I have a smooth interpolated value of the patch corners for subsequent vertices. When using the height value derived from the sampler, all I receive is a flat plane. When I multiply that value by a hundred, the height of the plane increases by around a hundred leading me to believe the alpha value is constantly one.
Here is the GLSL evaluation shader and the texture setup.
#version 430
layout(triangles, equal_spacing, ccw) in;
uniform mat4 camera;
uniform mat4 model;
uniform sampler2D terrain;
//uniform float lod_factor;
uniform float size;
in vec4 WorldPos_ES_in[];
in vec2 TexCoord_ES_in[];
in vec3 Normal_ES_in[];
out vec4 WorldPos_FS_in;
out vec2 TexCoord_FS_in;
out vec3 Normal_FS_in;
vec3 interpolate3D(vec3, vec3, vec3);
vec2 interpolate2D(vec2, vec2, vec2);
void main()
{
// Interpolate the attributes of the output vertex using the barycentric coordinates
TexCoord_FS_in = interpolate2D(TexCoord_ES_in[0], TexCoord_ES_in[1], TexCoord_ES_in[2]);
Normal_FS_in = interpolate3D(Normal_ES_in[0], Normal_ES_in[1], Normal_ES_in[2]);
Normal_FS_in = normalize(Normal_FS_in);
WorldPos_FS_in = vec4(interpolate3D(WorldPos_ES_in[0].xyz, WorldPos_ES_in[1].xyz, WorldPos_ES_in[2].xyz),1);
vec2 position=WorldPos_FS_in.xz;
float Displacement = texture(terrain, position/size).a;
//gl_Position = camera*model * WorldPos_FS_in;
gl_Position = camera*model * vec4(WorldPos_FS_in.x, Displacement,WorldPos_FS_in.z, 1.0);
}
vec2 interpolate2D(vec2 v0, vec2 v1, vec2 v2)
{
return vec2(gl_TessCoord.x) * v0 + vec2(gl_TessCoord.y) * v1 + vec2(gl_TessCoord.z) * v2;
}
vec3 interpolate3D(vec3 v0, vec3 v1, vec3 v2)
{
return vec3(gl_TessCoord.x) * v0 + vec3(gl_TessCoord.y) * v1 + vec3(gl_TessCoord.z) * v2;
}
and
glActiveTexture(GL_TEXTURE1);
GLuint tex2 = createTerrainMap();
glBindTexture(GL_TEXTURE_2D, tex2);
shader->setUniform("terrain", 1);
static GLuint createTerrainMap(){
GLuint texName;
glGenTextures(1, &texName);
glBindTexture(GL_TEXTURE_2D, texName);
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_S, GL_REPEAT);
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, GL_REPEAT);
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_NEAREST);
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_NEAREST);
glTexImage2D(GL_TEXTURE_2D, 0, GL_RGBA32F, size+1, size+1, 0, GL_RGBA, GL_FLOAT, terrainM);
return texName;
}
terrainM is declared as
GLfloat terrain[size+1][size+1][4];
As mentioned, using the vertex coordinates yields the correct result but defeats the purpose of the displacement map. In addition, I use another texture from a file as GL_TEXTURE1 which is TexCoord_ES_in and it is for the fragment shader and correctly applied. Any ideas to what is causing the flat plane instead of a displaced value?

Answer 1

Since the TEC does not provide data about the position of the triangle outside of the barycentric coordinates inside of it. Using the interpolated data for the triangle is useless. In my situation where the world coordinates is from 0 to an arbitrary amount, another set of UV coordinates is needed to find the correct height.