5 replies to this topic

[assainator]

Hello,

Last week I've run into a problem but can't find what's causing the problem.

The problem is as follows. I have a sphere and a light source. When the sphere isn't rotated, the lighting looks fine:


But as soon as I try to rotate it, the lighting get's all wrong. The picture below shows the sphere when it's rotated 90 degrees around the y-axis.



My first thought is that for some reason the normals aren't rotated at all or not rotated correctly.

I'm using GLSL and OpenGL 2.

I think shaders sources are useful:
vertex shader

// The diffuse value
varying float diffuse_value;

// The normalized light position
uniform vec3 NormalizedLightDirection;

void main()
{
    // Calculate the actual normal
    vec3 vertex_normal = normalize(gl_Normal * gl_NormalMatrix);

    // Calculate the diffuse value
    diffuse_value = max(dot(vertex_normal, NormalizedLightDirection), 0.0);

    // Set vertex position
    gl_Position = gl_ModelViewProjectionMatrix * (gl_Vertex);

    gl_FrontColor = gl_Color;
}

fragment shader:

varying float diffuse_value;

uniform vec4 DiffuseColor;

void main()
{
// Set the final color by multiplying the diffuse color with the diffuse value and then adding the ambient lighting
    gl_FragColor = vec4(1.0) * diffuse_value;
}

I appreciate any advice anybody can give me.

[SaTANO]

Correct this

vec3 vertex_normal = normalize(gl_NormalMatrix * gl_Normal );

OpenGL use column major matrices (same as your gl_Position calculation)

[Burnt_Fyr]

Hello,

Last week I've run into a problem but can't find what's causing the problem.

The problem is as follows. I have a sphere and a light source. When the sphere isn't rotated, the lighting looks fine:


But as soon as I try to rotate it, the lighting get's all wrong. The picture below shows the sphere when it's rotated 90 degrees around the y-axis.



My first thought is that for some reason the normals aren't rotated at all or not rotated correctly.

I'm using GLSL and OpenGL 2.

I think shaders sources are useful:
vertex shader

// The diffuse value
varying float diffuse_value;

// The normalized light position
uniform vec3 NormalizedLightDirection;

void main()
{
    // Calculate the actual normal
    vec3 vertex_normal = normalize(gl_Normal * gl_NormalMatrix);

    // Calculate the diffuse value
    diffuse_value = max(dot(vertex_normal, NormalizedLightDirection), 0.0);

    // Set vertex position
    gl_Position = gl_ModelViewProjectionMatrix * (gl_Vertex);

    gl_FrontColor = gl_Color;
}

fragment shader:

varying float diffuse_value;

uniform vec4 DiffuseColor;

void main()
{
// Set the final color by multiplying the diffuse color with the diffuse value and then adding the ambient lighting
    gl_FragColor = vec4(1.0) * diffuse_value;
}

I appreciate any advice anybody can give me.

Your Normalized light direction should be in the same space as the normal, and is not the direction the light is facing, but the direction from point to light. assuming that the gl_Normal matrix is the matrix translating from object space to world space, and that Normalized Light Direction is the vector that a directional light is pointing, use the inverse.

diffuse_value = max(dot(vertex_normal, -NormalizedLightDirection), 0.0);

if that doesn't work, check your gl_NormalMatrix to be sure that it is indeed what it should be. (identity for an object with no transforms, or a rotation matrix if you do have some)

[dpadam450]

// Calculate the actual normal vec3 vertex_normal = normalize( gl_NormalMatrix* gl_Normal);
NormalizedLightDirection = normalize( gl_NormalMatrix* NormalizedLightDirection); // Calculate the diffuse value diffuse_value = max(dot(vertex_normal, NormalizedLightDirection), 0.0);

[assainator]

Correct this

vec3 vertex_normal = normalize(gl_NormalMatrix * gl_Normal );

OpenGL use column major matrices (same as your gl_Position calculation)

That did the trick!

Thanks a lot for all the replies.

[Burnt_Fyr]

Correct this

vec3 vertex_normal = normalize(gl_NormalMatrix * gl_Normal );

OpenGL use column major matrices (same as your gl_Position calculation)

!FACEPALM