Normal mapping working incorrectly, weird half-light effect

Question

We are trying to implement normal mapping in our 2D Game Engine and get weird effect. If normal is set manually like that vec3 Normal = vec3(0.0, 0.0, 1.0) light works correctly, but we dont get "deep" effect that we want to achieve by normal mapping: But if we get normal using normal map texture: vec3 Normal = texture(NormalMap, TexCoord).rgb it doesn't work at all. What should not be illuminated is illuminated and vice versa (such as the gaps between the bricks). And besides this, a dark area is on the bottom (or top, depending on the position of the light) side of the texture. Although the texture of the normal map itself looks fine: This is our fragment shader:

#version 330 core
layout (location = 0) out vec4 FragColor;

in vec2 TexCoord;
in vec2 FragPos;

uniform sampler2D OurTexture;
uniform sampler2D NormalMap;

struct point_light
{
    vec3 Position;
    vec3 Color;
};

uniform point_light Light;

void main()
{
    vec4 Color = texture(OurTexture, TexCoord);
    vec3 Normal = texture(NormalMap, TexCoord).rgb;

    if (Color.a < 0.1)
        discard;

    vec3 LightDir = vec3(Light.Position.xy - FragPos, Light.Position.z);

    float D = length(LightDir);

    vec3 L = normalize(LightDir);
    Normal = normalize(Normal * 2.0 - 1.0);

    vec3 Diffuse = Light.Color * max(dot(Normal, L), 0);
    vec3 Ambient = vec3(0.3, 0.3, 0.3);

    vec3 Falloff = vec3(1, 0, 0);

    float Attenuation = 1.0 /(Falloff.x + Falloff.y*D + Falloff.z*D*D);
    vec3 Intensity = (Ambient + Diffuse) * Attenuation;

    FragColor = Color * vec4(Intensity, 1);
}

And vertex as well:

#version 330 core
layout (location = 0) in vec2 aPosition;
layout (location = 1) in vec2 aTexCoord;

uniform mat4 Transform;
uniform mat4 ViewProjection;

out vec2 FragPos;
out vec2 TexCoord;

void main()
{
    gl_Position = ViewProjection * Transform * vec4(aPosition, 0.0, 1.0);
    TexCoord = aTexCoord;
    FragPos = vec2(Transform * vec4(aPosition, 0.0, 1.0));
}

I google about that and found some people that get the same result, but their questions remained unanswered. Any idea of what is the cause?

Answer 1

What texture format are you using for the normal map? SRGB, SNORM, etc? That might be the issue. Try UNORM.

Additionally, since you are not using a tangent space, make sure the plane's Z axis aligns with the Z axis of the normals. Also OGL reads Y in the reversed direction, so you need to flip the Y coordinates of the normals that you read from the normal map. Alternatively, you can use a reversed Y normal map (green pointing down).