Matrix4 to GLSL uniform value

Question

So I'm creating a simple game in C++ with OpenGL API (Using SDL2 and GLEW).

I created simple shader program, and I started creating uniform variable loaders (Like a Vector3, float) but I really don't know how to load 4x4 Matrix to uniform variable with glUniformMatrix4fv.

How to put those values from my Matrix4 to this function?

You just give it a pointer to the matrix, what's the problem? — harold, Jan 14 '16 at 16:34
Try this: http://stackoverflow.com/questions/25342594/passing-uniform-4x4-matrix-to-vertex-shader-program — Alan, Jan 14 '16 at 16:37
So what should I put inside "count" value, I guess false is going to "transpose" value and the next variable is value. But how should I put it inside this function? Create F32 mat[3][3]; and put mat inside this function? — skprime, Jan 14 '16 at 16:37
@skprime eh no the 3 in the declaration of the static array is the length of it (where 0 is the empty array and 1 has 1 element). — ratchet freak, Jan 14 '16 at 16:41
that's undefined behavior and you are probably thrashing some other poor struct's data. — ratchet freak, Jan 14 '16 at 16:44
@skprime that means the index goes from zero to size minus one, the size is not size plus one (obviously, because what does that even mean) — harold, Jan 14 '16 at 16:45

score 2 · Accepted Answer · answered Jan 14 '16 at 16:43

glUniformMatrix4fv expects a pointer to a buffer with 16 floats.

float[16] m1;
struct mat4{
    float m00, m01, m02, m03;
    float m10, m11, m12, m13;
    float m20, m21, m22, m23;
    float m30, m31, m32, m33;
};
mat4 m2

The following are all valid:

glUniformMatrix4fv(MatUniformLoc, 1, GL_FALSE, &m2);
glUniformMatrix4fv(MatUniformLoc, 1, GL_FALSE, m1);

From the documentation:

count

For the matrix (glUniformMatrix*) commands, specifies the number of matrices that are to be modified. This should be 1 if the targeted uniform variable is not an array of matrices, and 1 or more if it is an array of matrices.

[...]

value

For the vector and matrix commands, specifies a pointer to an array of count values that will be used to update the specified uniform variable.

Matrix4 to GLSL uniform value

1 Answers1