CODEWITHSUNDEEP
c++opengl
user3591811
user3591811

Reputation: 95

Passing multiple attributes to OpenGL shaders

I have interleaved [position, colour, normal] data in an array that I then pass to the vertex shader. The vertex shader only seems to pick up the first two values [position and colour]. What is preventing it from getting the normal data as well?

data store

struct c_vertex{
GLfloat x;
GLfloat z;
GLfloat y;
GLfloat r;
GLfloat g;
GLfloat b;
GLfloat nx;
GLfloat nz;
GLfloat ny;
};

array

c_vertex vertex_store[max_bins][max_bins];

having assigned values to the elements of the array [which works correctly as I'll demonstrate later] the draw routine:

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

glGenBuffers(1,&VertexVBoid);
glBindBuffer (GL_ARRAY_BUFFER, VertexVBoid);
glBufferData(GL_ARRAY_BUFFER,sizeof(vertex_store),&(vertex_store[0][0].x),GL_STATIC_DRAW);

glGenBuffers(1, &IndexVBOID);
glBindBuffer(GL_ELEMENT_ARRAY_BUFFER, IndexVBOID);
glBufferData(GL_ELEMENT_ARRAY_BUFFER, sizeof(vertex_order), vertex_order, GL_STATIC_DRAW);

glBindBuffer (GL_ARRAY_BUFFER, VertexVBoid);
glVertexAttribPointer (0, 3, GL_FLOAT, GL_FALSE, sizeof(c_vertex), BUFFER_OFFSET(0));
glVertexAttribPointer (1, 3, GL_FLOAT, GL_FALSE, sizeof(c_vertex), BUFFER_OFFSET(3*sizeof(vertex_store[0][0].x)));
glVertexAttribPointer (2, 3, GL_FLOAT, GL_FALSE, sizeof(c_vertex), BUFFER_OFFSET(6*sizeof(vertex_store[0][0].x)));

glEnableVertexAttribArray (0);
glEnableVertexAttribArray (1);
glEnableVertexAttribArray (2);

glBindVertexArray (vao);

glDrawElements(GL_TRIANGLES, (max_bins-1)*(max_bins-1)*2*3, GL_UNSIGNED_INT, (void *) 0);
glDisableVertexAttribArray (0);
glDisableVertexAttribArray (1);
glDisableVertexAttribArray (2);
};

Vertex shader

attribute vec3 kposition;
attribute vec3 kcolor;
attribute vec3 knormal;

uniform mat4 MVP;
varying vec4 kolor;

void main()
{
    kolor = vec4(knormal,1.0);
    gl_Position = MVP*vec4(kposition,1.0);
}

fragment shader:

varying vec4 kolor;

void main(){
    gl_FragColor=kolor;
}

the normal values are the same as the colour values

if I swap the offsets in

glVertexAttribPointer (1, 3, GL_FLOAT, GL_FALSE, sizeof(c_vertex), BUFFER_OFFSET(3*sizeof(vertex_store[0][0].x)));
glVertexAttribPointer (2, 3, GL_FLOAT, GL_FALSE, sizeof(c_vertex), BUFFER_OFFSET(6*sizeof(vertex_store[0][0].x)));

to

glVertexAttribPointer (1, 3, GL_FLOAT, GL_FALSE, sizeof(c_vertex), BUFFER_OFFSET(6*sizeof(vertex_store[0][0].x)));
glVertexAttribPointer (2, 3, GL_FLOAT, GL_FALSE, sizeof(c_vertex), BUFFER_OFFSET(3*sizeof(vertex_store[0][0].x)));

then I get the normal data being used as the colour data in the shaders

if i have the offsets as

glVertexAttribPointer (1, 3, GL_FLOAT, GL_FALSE, sizeof(c_vertex), BUFFER_OFFSET(3*sizeof(vertex_store[0][0].x)));
glVertexAttribPointer (2, 3, GL_FLOAT, GL_FALSE, sizeof(c_vertex), BUFFER_OFFSET(6*sizeof(vertex_store[0][0].x)));

if I change the shader from 

attribute vec3 kposition;
attribute vec3 kcolor;
attribute vec3 knormal;

to

attribute vec3 kposition;
attribute vec3 knormal;
attribute vec3 kcolor;

knormal and kcolor have the same values - the colour attribute.

What is the error in my code?

Upvotes: 1

Views: 521

Answers (1)

IronMensan
IronMensan

Reputation: 6821

There are no guarantees about the mapping between the attributes in the shader and attribute index. Use glGetAttribLocation to query the shader for each attribute.

GLint positionIndex = glGetAttribLocation(myProgramID, "kposition");
glVertexAttribPointer (positionIndex, 3, GL_FLOAT, GL_FALSE, sizeof(c_vertex), BUFFER_OFFSET(0));
glEnableVertexAttribArray (positionIndex);

GLint colorIndex = glGetAttribLocation(myProgramID, "kcolor");
glVertexAttribPointer (colorIndex, 3, GL_FLOAT, GL_FALSE, sizeof(c_vertex), BUFFER_OFFSET(3*sizeof(vertex_store[0][0].x)));
glEnableVertexAttribArray (colorIndex);

GLint normalIndex = glGetAttribLocation(myProgramID, "knormal");
glVertexAttribPointer (normalIndex, 3, GL_FLOAT, GL_FALSE, sizeof(c_vertex), BUFFER_OFFSET(6*sizeof(vertex_store[0][0].x)));
glEnableVertexAttribArray (normalIndex);

Upvotes: 3

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