GLSL Lighting Acting As Flat - Normals Issue?

Question

I am currently working on an OpenGL framework and recently created a .ply (Polygon File Format) mesh importer. With the importer working, I wanted to try out a simple lighting shader on an imported mesh but am running into issues.

The mesh is a low-res version of the famous Stanford Bunny taken from the Stanford 3D Scanning Repository and was initially imported into Blender to verify correctness and then exported once again in order to get nX, nY, nZ values as opposed to confidence and intensity. This file can be found at http://pastebin.com/raw.php?i=xRmLYN0s

What is happening is that the lighting shader is acted like a flat shader that changes color based on camera orientation. Images are included at the end of this post.

The shader is from the OpenGL Super Bible and is described as Simple diffuse, directional, and vertex based light:

Vertex

#version 140

uniform mat4 mvMatrix;
uniform mat4 pMatrix;
uniform vec4 vColor;

in vec4 vVertex;
in vec3 vNormal;

out vec4 vFragColor;

void main( void )
{
    mat3 mNormalMatrix;

    mNormalMatrix[0] = mvMatrix[0].xyz;
    mNormalMatrix[1] = mvMatrix[1].xyz;
    mNormalMatrix[2] = mvMatrix[2].xyz;

    vec3 vNorm = normalize(mNormalMatrix * vNormal);
    vec3 vLightDir = vec3(0.0, 0.0, 1.0);

    float fDot = max(0.0, dot(vNorm, vLightDir)); 
    vFragColor.rgb = vColor.rgb * fDot;
    vFragColor.a = vColor.a;

    gl_Position = ( pMatrix * mvMatrix ) * vVertex;
}

Fragment

#version 140

in vec4 vFragColor;

void main( void )
{
    gl_FragColor = vFragColor;
}

Could this be an issue with the normals? I have verified that they are being extracted from the model file properly and they are then fed into a VAO:

    glBindVertexArray( m_VAO );
    glEnableVertexAttribArray( ToolBox::Math::GLSL_ATTR::NORMAL );
    glBindBuffer( GL_ARRAY_BUFFER, m_NormalBuffer );
    glBufferData( GL_ARRAY_BUFFER, sizeof( GLfloat ) * num_elements, normals, GL_STATIC_DRAW );
    glVertexAttribPointer( ToolBox::Math::GLSL_ATTR::NORMAL, 3, GL_FLOAT, GL_FALSE, 0, ( const GLvoid* )0 );
    glBindVertexArray( 0 );
    glBindBuffer( GL_ARRAY_BUFFER, 0 );

This is the same VAO used for the spatial (x,y,z) information and has been used in the past for color and texture values. Also the shaders are parsed by a custom ShaderManager class, and the vNormal attribute has been confirmed to be bound to the same index (ToolBox::Math::GLSL_ATTR::NORMAL aka 2) via glBindAttribLocation as the normal buffer in the above snippet.

From what I can tell, the normals should be being passed correctly from the file to the shader. But if I set vFragColor.rgb = vNormal.xyz in the vertex shader, the bunny comes out a solid red. Thats not good, is it?

So any ideas why the shader is not working? Is it bad? Are the normal not being passed? Something else?

Thank you for any assistance you may be able to provide. If you need more information, just let me know.

Images

Rotating around the bunny:

enter image description here

Setting vFragColor.rgb = vNormal.xyz;

enter image description here

Model in Blender (confirming its correctness)

enter image description here

Looks like your normals are definitely not getting passed. I'm going to guess that the error is not something in the snippets you've posted. Can you check glGetError and make sure it is zero, and post a little more context (any shader init, linking, attrib binding, etc etc). — Tim
I checked for errors in various places but did not find any. Relevant code snippets follow: pastebin.com/eetAmKTu (Shader building), pastebin.com/Cz3ZYdEt (attribute binding), pastebin.com/jTafh7ia (the full normal VAO build). The full source can also be found at github.com/ssell/glToolBox with the relevant files being ToolBox_Batch.cpp, ToolBox_Batch_Module_StanfordPLY.cpp, ToolBox_Shaders.cpp; Though the code is long and has little internal documentation as of now. — ssell
Note there is an error in the full VAO snippet where I never generate the normal buffer. This isn't the issue and the line must have been cut accidentally while trying to figure this out. — ssell

ssell ssell · Accepted Answer · 2012-08-16T01:12:24

The issue was in the attribute binding. Somehow in my shader parser I forgot to differentiate between the true line of code being read and the one set to all uppercase for case-insensitive comparison checking.

This caused the GLSL_ATTR::NORMAL index to be bound to VNORMAL opposed to vNormal. Oddly this issue never reared itself during positional/color/texture work. Thanks to @Tim for attempting to help me with this issue that was simply a silly typo.

Finally, the bunny lighted as it was meant to be:

enter image description here

GLSL Lighting Acting As Flat - Normals Issue?

1 Answers