My Terrain shader

terrain_vertex.glsl

precision highp float;
precision highp int;

layout(location = 0) in vec3 a_pos;
layout(location = 1) in vec2 uv;
layout(location = 2) in vec3 col;

out vec3 v_col;
out float v_toSunDot;

uniform sampler2D HeightMapOffset;

layout(std140) uniform vertex {
    mat4 ortho;
};


vec4 uv_lut[4] = vec4[4](
    vec4(1.0, 0.0, 1.0, 0.0),  // left bottom
    vec4(1.0, 0.0, 0.0, 1.0),  // left top
    vec4(0.0, 1.0, 1.0, 0.0),  // right bottom
    vec4(0.0, 1.0, 0.0, 1.0)); // right top

vec3 size_lut[4] = vec3[4](
    vec3(0.0,  0.0, 1.0),  // left top
    vec3(0.0,  0.0, 0.0),  // right top
    vec3(1.0,  0.0, 1.0),  // left bottom
    vec3(1.0,  0.0, 0.0)); // right bottom


vec4 calculate_position(int vertexId) {
    vec4 temp = uv_lut[vertexId];
    vec2 calculated_uv = vec2((temp.x + temp.y), (temp.z + temp.w));
    int x_vertex_offset = vertexId / 2;
    int y_vertex_offset = vertexId % 2;

    float map_size = 200.0; 
    int map_x = 200;
    int map_z = 200;
    v_col = col;

    float x_index = float(gl_InstanceID / map_x);
    float z_index = float(gl_InstanceID % map_z);
    
    v_col.r = (z_index / map_size) * 1.0;
    
    vec3 size =  10.0 * size_lut[vertexId];

    

    float shift_amount = 1.0 / map_size;
    vec2 temp_uv = vec2((temp.x + temp.y) / map_size, (temp.z + temp.w) / map_size);
    temp_uv.x += shift_amount * (x_index + float(x_vertex_offset));
    temp_uv.y += shift_amount * (z_index - float(y_vertex_offset));

    vec4 height_offset_sample = texture(HeightMapOffset, temp_uv);

    vec3 pos = a_pos + size;
    pos.x = pos.x + x_index * 10.0;
    pos.z = pos.z + z_index * 10.0;
    pos.y = height_offset_sample.r * map_size;
    return ortho * vec4(pos, 1.0);
}


void main() {

    vec4 a = calculate_position((gl_InstanceID + 1) % 4);
    vec4 b = calculate_position((gl_InstanceID + 2) % 4);
    vec4 final = calculate_position(gl_VertexID);

    vec4 bort = b - final;
    vec4 ernie = a - final;

    vec3 normla = cross(vec3(bort), vec3(ernie));


	vec3 lightToPoint = normalize(vec3(0.0, 20000.0, 0.0) - vec3(final));
    float toSunDot = dot(lightToPoint, normla);
	if (toSunDot < 0.1) {
		toSunDot = 0.1;
	}

    v_toSunDot = toSunDot;

    gl_Position = final;
}