Use normals as colors in OpenGL using assimp

Question

I exported the suzanne model from blender(Monkey head) as a .obj file and I can only see it when I use the RGB values in the fragment shader. e.g. frag_color = vec4( 1.0, 0.0, 0.0, 1.0 ); to make the model red. But it just looks like a deformed texture unless I rotate it

Front view

I want to use the normals as colors so that I can see specific details in the face, etc. I bound the normals to vertex position 1.

    if ( mesh -> HasNormals() )
    {

        normals = ( GLfloat * ) malloc( * pointCount * 3 * sizeof( GLfloat ) );

        for ( int i = 0; i < * pointCount; i++ )
        {

            const aiVector3D * vn = &( mesh -> mNormals[ i ] );

            normals[ i * 3 ] = ( GLfloat ) vn -> x;
            normals[ i * 3 + 1 ] = ( GLfloat ) vn -> y;
            normals[ i * 3 + 2 ] = ( GLfloat ) vn -> z;

        }

        GLuint vbo;

        glGenBuffers( 1, &vbo );
        glBindBuffer( GL_ARRAY_BUFFER, vbo );
        glBufferData( GL_ARRAY_BUFFER, 3 * * pointCount * sizeof( GLfloat ), normals, GL_STATIC_DRAW );
        glVertexAttribPointer( 1, 3, GL_FLOAT, GL_FALSE, 0, NULL );
        glEnableVertexAttribArray( 1 );

        free( normals );

    }

And I bound 1 to vertex_normal right after attaching the shaders but right before linking.

glAttachShader( program, vertShader );
glAttachShader( program, fragShader );

glBindAttribLocation( program, 0, "vertex_position" );
glBindAttribLocation( program, 1, "vertex_normal" );

glLinkProgram( program );

These are my shaders

vertshader.shader

#version 330

in vec3 vertex_position;
in vec3 vertex_normal;

uniform mat4 proj, view, model;

out vec3 normals;

void main()
{

    normals = vertex_normal;

    gl_Position = proj * vec4( vec3( view * model * vec4( vertex_position, 1.0 ) ), 1.0 );

}

fragshader.shader

#version 330

in vec3 normals;

out vec4 fragment_color;

void main()
{       

    fragment_color = vec4( normals, 1.0 );

}

But this only outputs a black screen. I know the model is loading because I can color it red like above. I tried importing vertex_normal directly into the frag shader, that didn't work, I also tried normalizing normals and that didn't change the effect neither.

So how can I use the models normals as colors in the fragment shader?

What you're doing looks reasonable at first sight. Checking the (hopefully) obvious: You verified that the model actually has normals? The code inside the if (mesh->HasNormals()) is executed, and you see what looks like reasonable vectors if you step through it in a debugger, or log the values? — Reto Koradi
Also, one way to narrow down the problem is to set the background color to something other than black. That will tell you if the model is rendered black, or not at all. — Reto Koradi
Hmm, I didn't consider the possibility of it not having normals since I was able to flip them and export them in blender. I tried using a model with flipped normals and un-flipped normals. I haven't tried changing the background yet though, I'll let you know the results once I render it — NukingDragons
So I changed the background to red, and I see the model being rendered as black. Does this mean it doesn't have normals or that the normals aren't being drawn because of a syntax error, etc? — NukingDragons

NukingDragons NukingDragons · Accepted Answer · 2014-06-17T05:20:56

Ok, I found a fix. Apparently it was blenders fault. There is a side panel on what I want to export with my mesh, and Write normals wasn't checked. Thanks to Reto Koradi, I didn't think it was possible for a mesh to be written without normals.

enter image description here

Use normals as colors in OpenGL using assimp

1 Answers