Question

I’ve just finished creating a simple rectangle in OpenGL 3.2, now I want to add lighting support. However, whenever I try to move my normals to the fragment shader, nothing appears. If I comment out that line, it works perfectly again. What would be the reason causing this? Nothing shows up in error log.

Vertex Shader:

#version 150

in vec4 position;
in vec3 inNormal;

out vec3 varNormal;

uniform mat4 modelViewProjectionMatrix;

void main()
{
    //varNormal = inNormal; //If I uncomment this line, nothing shows up    
gl_Position = modelViewProjectionMatrix * position;
}

Fragment Shader:

#version 150

in vec3 varNormal;

out vec4 fragColor;

void main()
{
fragColor = vec4(1, 1, 1, 1);   
}

And passing the normals:

GLuint posAttrib = 0;
GLuint normalAttrib = 1;

glBindAttribLocation(program, posAttrib, "position");
glBindAttribLocation(program, normalAttrib, "normalAttrib");

//Building the VAO's/VBO's
GLfloat posCoords[] = 
{
    -10, 0.0, -10,
    -10, 0.0, 10,
    10, 0.0, 10,
    10, 0.0, -10,   
};

GLfloat normalCoords[] = 
{
    0, 0, 1,
    0, 0, 1,
    0, 0, 1,
    0, 0, 1
};

glGenVertexArrays(1, &vaoName);
glBindVertexArray(vaoName);

GLuint posBuffer;
glGenBuffers(1, &posBuffer);
glBindBuffer(GL_ARRAY_BUFFER, posBuffer);
glBufferData(GL_ARRAY_BUFFER, sizeof(posCoords), posCoords, GL_STATIC_DRAW);
glEnableVertexAttribArray(posAttrib);   
glVertexAttribPointer(posAttrib, 3, GL_FLOAT, GL_FALSE, 0, 0);

GLuint normalBuffer;        
glGenBuffers(1, &normalBuffer);
glBindBuffer(GL_ARRAY_BUFFER, normalBuffer);
glBufferData(GL_ARRAY_BUFFER, sizeof(normalCoords), normalCoords, GL_STATIC_DRAW);
glEnableVertexAttribArray(normalAttrib);
glVertexAttribPointer(normalAttrib, 3, GL_FLOAT, GL_FALSE, 0, 0);

I haven’t tried putting all of my position and normal coords in a single VBO, but I’d prefer to not resort to that method.

Answer 1

Probably the most bizarre reason to fix this, but it works.

First of all, make sure you know how the OpenGL Profiler works. There’s a tutorial provided by the Apple Docs

Set a breakpoint before/after glDrawElements (or glDrawArray depending on what you’re using)

Then look at your program’s vertex attributes and make sure the locations are in order.

If they aren’t, rearrange them.

From (or anything else):

enum
{
POSITION_ATTR = 0,
TEXTURE_ATTR=1,
NORMAL_ATTR=2,
};

To:

enum
{
NORMAL_ATTR = 0,
TEXTURE_ATTR=2,
POSITION_ATTR=1,
};

No idea how and why this is happening, but this is the solution to the problem.