glGetUniformLocation returns -1 for an array of struct in GLSL

Question

I'm trying to call glGetUniformLocation() on an array of struct. I read that I should use this name format: "uniformName[index].element", but the method always returns -1. I tried to delete the array and only use the structure and it worked so I guess that the problem might there. Here is the struct and the array in my fragment shader:

const int MAX_BLOCKS = 16;

struct sblock{

    vec4 color;
    float shineDamper;
    float reflectivity;
};

uniform sblock blocks[MAX_BLOCKS];

And here is my call:

for(int i = 0; i < 16; i++) {
            location_block_color[i] = super.getUniformLocation("blocks["+i+"].color");
            location_block_reflectivity[i] = super.getUniformLocation("blocks["+i+"].reflectivity");
            location_block_shineDamper[i] = super.getUniformLocation("blocks["+i+"].shineDamper");
            System.out.println(location_block_color[i] + " " + location_block_reflectivity[i] + " " + location_block_shineDamper[i]); // prints -1 -1 -1 ...
        }

getUniformLocation method:

protected int getUniformLocation(String uniformName) {
        return GL20.glGetUniformLocation(programID, uniformName);
    }

and this how I create programID (before anything else):

vertexShaderID = loadShader(vertexFile, GL20.GL_VERTEX_SHADER);
        fragmentShaderID = loadShader(fragmentFile, GL20.GL_FRAGMENT_SHADER);
        programID = GL20.glCreateProgram();

My question is what is happening here and what am I doing wrong? Thanks for your help.

EDIT 1:

Here is my full fragment shader:

#version 400 core

const int MAX_LIGHTS = 16;
const int MAX_BLOCKS = 16;

struct sblock{

    vec4 color;
    float shineDamper;
    float reflectivity;
};

uniform sblock blocks[MAX_BLOCKS];


in int block_id_out;
in vec3 unitNormal;
in vec3 lightVector[MAX_LIGHTS];
in vec3 directionalLightFinalColour;
in vec3 directionalLightReflected;

in vec3 toCameraVector;

in float visibility;

out vec4 outColor;


uniform float ambientLight;
uniform vec3 skyColor;

uniform vec3 lightColour[MAX_LIGHTS];
uniform vec3 attenuation[MAX_LIGHTS];
uniform int lightCount;
uniform vec3 directionalLightColour;
uniform vec3 directionalLightDirection;

vec3 calculateDiffuse(vec3 unitNormal, vec3 unitLightVector, vec3 lightColour, float attFactor){
    float nDotl = dot(unitNormal,unitLightVector);
    float brightness = max(nDotl,0);
    return (brightness * lightColour) / attFactor;
}


vec3 calculateSpecular(vec3 unitNormal, vec3 unitLightVector, vec3 unitToCameraVector, float shineDamper, float reflectivity, vec3 lightColour, float attFactor){
    vec3 reflectedLightDirection = reflect(-unitLightVector,unitNormal);
    float specularFactor = max(dot(reflectedLightDirection, unitToCameraVector),0.0);
    float dampedFactor = pow(specularFactor,shineDamper);
    return (dampedFactor * reflectivity * lightColour) / attFactor;
}

void main(void){

    vec3 totalDiffuse = vec3(0.0);
    vec3 totalSpecular = vec3(0.0);
        
    vec3 unitToCameraVector = normalize(toCameraVector);

    for(int i = 0; i < lightCount;i++){
        vec3 unitLightVector = normalize(lightVector[i]);
        float lightDistance = length(lightVector[i]);
        
        float attFactor = attenuation[i].x + attenuation[i].y*lightDistance + attenuation[i].z*lightDistance*lightDistance;
        
        totalSpecular += calculateSpecular(unitNormal, unitLightVector, unitToCameraVector, blocks[block_id_out].shineDamper, blocks[block_id_out].reflectivity, lightColour[i], attFactor);
        totalDiffuse += calculateDiffuse(unitNormal, unitLightVector, lightColour[i], attFactor);
    }
    
    totalDiffuse += directionalLightFinalColour;
    totalSpecular += pow(max(dot(directionalLightReflected,unitToCameraVector),0.0),blocks[block_id_out].shineDamper)*blocks[block_id_out].reflectivity*directionalLightColour;
    totalDiffuse = max(totalDiffuse,ambientLight);
    
    outColor = vec4(totalDiffuse,1.0) * blocks[block_id_out].color + vec4(totalSpecular,1.0);
    outColor = mix(vec4(skyColor,1.0),outColor,visibility);
}

EDIT 2:

Here is my VertexShader:

#version 400 core
const vec4 normals[] = vec4[6](vec4(1,0,0,0),vec4(0,1,0,0),vec4(0,0,1,0),vec4(-1,0,0,0),vec4(0,-1,0,0),vec4(0,0,-1,0));
const int MAX_LIGHTS = 16;

in vec3 position;
in int block_id;
in int normal;

out int block_id_out;
out vec3 unitNormal;
out vec3 lightVector[MAX_LIGHTS];
out vec3 directionalLightFinalColour;
out vec3 directionalLightReflected;
out vec3 toCameraVector;
out float visibility;

uniform mat4 transformationMatrix;
uniform mat4 projectionMatrix;
uniform mat4 viewMatrix;
uniform vec3 lightPosition[MAX_LIGHTS];
uniform vec3 directionalLight;
uniform vec3 directionalLightColor;

uniform int lightCount;

uniform float fogDensity;
uniform float fogGradient;

void main(void){

    vec4 worldPosition = transformationMatrix * vec4(position,1.0);
    vec4 positionRelativeToCam = viewMatrix * worldPosition;
    
    gl_Position = projectionMatrix * positionRelativeToCam;
    block_id_out = block_id;
    unitNormal = normalize((transformationMatrix * normals[normal]).xyz);
    
    for(int i = 0; i < lightCount;i++){
        lightVector[i] = lightPosition[i] - worldPosition.xyz;
    }
    directionalLightFinalColour = max(dot(unitNormal, directionalLight),0)*directionalLightColor;
    directionalLightReflected = reflect(-directionalLight,unitNormal);
    
    toCameraVector = (inverse(viewMatrix) * vec4(0.0,0.0,0.0,1.0)).xyz - worldPosition.xyz;
    
    visibility = clamp(exp(-pow(length(positionRelativeToCam.xyz)*fogDensity,fogGradient)),0.0,1.0);
}

Answer 1

I think that @Rabbid76 answer is correct, but I found a more satisfying workaround. I defined the struct and the uniform in the vertex shader, and then pass the correct values for color, shinedamper and reflectivity to the fragment shader. This makes more sense since I only want to access the values for each vertex and they are going to be same in the fragment shader, so doing it 3 times for each triangle is better than doing it hundreds of times for each pixel.