shaders – How do I choose terrain in GLSL (+openGL) by choosing 2D vertices positions struggling on day 4

Presumably the issue is with the interior codecs and my understanding of that, however I have been caught some time, acquired this form of approaching working fantastic on a extra straight ahead color picker, however right here I am choosing pos coordinates saved as information at places.

Could be actually grateful for anybody who will help me throguh this.

So I’ve a fbo, a texture2d attachment in shade 0 and primarily I move my vertices (XYZ) (GLfloat) to the vertex shader in location 0 ‘place’.

Since my terrain is a sq. at all times, 100×100 3000×3000 and many others, I solely want the X and Z since they’ll all be distinctive, so I out a vec2 of the place.XZ to the fragment shader after which within the fragment shader I do that on an if assertion

frag
...
structure(location = 0) out vec4 FragColor;
structure(location = 1 )out vec4 FragColor2;

primary...
if (terrainEditMode == 1)
{
   
   
   FragColor2 = vec4(vecIDs.x, vecIDs.y, 0.1,0.1);
}

I arrange the attachment like this

glGenFramebuffers(1, &terrainPickFBO);
        glBindFramebuffer(GL_FRAMEBUFFER, terrainPickFBO);
        glGenTextures(1, &terrainPickTexture);
        glBindTexture(GL_TEXTURE_2D, terrainPickTexture);

        glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_S, GL_CLAMP_TO_EDGE);
        glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, GL_CLAMP_TO_EDGE);
        glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_LINEAR);
        glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_LINEAR);
        glTexImage2D(GL_TEXTURE_2D, 0, GL_RGBA, window_width, window_height, 0, GL_RGBA, GL_UNSIGNED_BYTE, nullptr);
        glFramebufferTexture2D(GL_FRAMEBUFFER, GL_COLOR_ATTACHMENT1, GL_TEXTURE_2D, terrainPickTexture, 0);

and skim pixels on the certain fbo

GLuint pickpixelColor[4];
    glReadBuffer(GL_COLOR_ATTACHMENT1);
    //glReadPixels(xpos, ypos, 1, 1, GL_RGBA, GL_UNSIGNED_BYTE, &pixelColor);
    glReadPixels(static_cast<GLint>(xpos), static_cast<GLint>(ypos), 1, 1, GL_RGBA, GL_UNSIGNED_BYTE, &pickpixelColor2);

Then render:

glBindFramebuffer(GL_FRAMEBUFFER, terrain.terrainPickFBO);
GLenum drawBuffers[] = { GL_COLOR_ATTACHMENT0, GL_COLOR_ATTACHMENT1 };
glDrawBuffers(1, drawBuffers);
terrain.render();