GLSL shader issue - opengl

Question

I created two shaders for my program to render simple objects.
Vertex shader source:
#version 400 core
layout (location = 1) in vec4 i_vertexCoords;
layout (location = 2) in vec3 i_textureCoords;
layout (location = 3) in vec3 i_normalCoords;
layout (location = 4) in int i_material;
uniform mat4 u_transform;
out VertexData {
vec3 textureCoords;
vec3 normalCoords;
int material;
} vs_out;
void main() {
vs_out.textureCoords = i_textureCoords;
vs_out.material = i_material;
gl_Position = u_transform * i_vertexCoords;
vs_out.normalCoords = gl_Position.xyz;
}
Fragment shader source:
#version 400 core
struct MaterialStruct {
int ambientTexutre;
int diffuseTexture;
int specularTexture;
int bumpTexture;
vec4 ambientColor;
vec4 diffuseColor;
vec4 specularColor;
float specularComponent;
float alpha;
int illuminationModel;
};
in VertexData {
vec3 textureCoords;
vec3 normalCoords;
int material;
} vs_out;
layout (std140) uniform MaterialsBlock {
MaterialStruct materials[8];
} u_materials;
uniform sampler2D u_samplers[16];
out vec4 fs_color;
void main() {
MaterialStruct m = u_materials.materials[vs_out.material];
fs_color = vec4(m.diffuseColor.rgb, m.diffuseColor.a * m.alpha);
}
Program created with this two shaders renders picture 2
When I change main() function contents to next:
void main() {
MaterialStruct m = u_materials.materials[vs_out.material];
fs_color = vec4(m.diffuseColor.rgb * (vs_out.normalCoords.z + 0.5), m.diffuseColor.a * m.alpha);
}
It renders picture 1, but materials still exists (if I'm trying to select material from u_materials.materials manually it works). Shader thinks what vs_out.material is constant and equals 0, but it isn't. Data is not changed (excluding transformation matrix)
Could someone explain the solution of this problem?

Answer 1

The GLSL 4.5 spec states in section 4.3.4 "Input Variables":
Fragment shader inputs that are signed or unsigned integers, integer vectors, or any double-precision
floating-point type must be qualified with the interpolation qualifier flat.
You can't use interpolation with those types, and actually, your code shouldn't compile on a strict implementation.