glsl passing data array from vertex to tessellation control shader

Question

I am trying to pass a vec3 array from vertex shader to tessellation shader.

passing just one value works fine, but how to pass an array?

Vertex shader

#version 430
out vec3 data; //working!
out vec3 dataArray[2];
void main()
{
    gl_position = vec4(0,0,0,0);
    data = vec3(1,2,3);
    dataArray[0] = vec3(1,2,3);
    dataArray[1] = vec3(4,5,6);
}

tessellation controll shader

#version 430
layout (vertices = 3) out;

in vec3 data[]; //working!
in vec3 dataArray[2][]; // how to do this?

void main()
{
    ...
}

The error message is: error C7618: OpenGL/ES does not allow input array declarations with size not equal to gl_MaxPatchVertices

I also tried

in vec3 dataArray[2][gl_MaxPatchVertices]

But this also doesn't work.

Answer 1

in vec3 dataArray[2][]; // how to do this?

Arrays of arrays in GLSL work differently than you might expect. The array indices are read left-to-right. For example, vec2 var[2][3] is a 2-element array of 3-element arrays of vec2s.

What you want is an "unsized array of 2 element arrays of vec3". To do that, you need in vec3 dataArray[][2];.

Alternatively, you can declare the main type next to the type name and the array aggregation beside the variable name: in vec3[2] dataArray[];. GLSL allows this kind of split declaration style, where the array sizes on the type happen before the array sizes on the variable.

Answer 2

Change the output of the vertex shader to

out vec3[2] dataArray;

and the input to the tessellation control shader as

in vec3[2] dataArray[];

That should work. Alternatively you could also define the type of dataArray as a struct.