Getting a Matrix4x4 into a uniform buffer

[Abrynos]

Hey there :)

I am currently working on optimizing some stuff and I am trying to extract things like the projection matrix for my application from each shader setting a uniform into a uniform buffer. How do I properly put the System.Numerics.Matrix4x4 I have in my normal memory into that buffer using Silk.NET?

You can take below code as an example (tho i've wrapped everything nicely in classes).

GL gl = ...;
uint matrixSize = (uint) Marshal.SizeOf<Matrix4x4>();
uint bytes = matrixSize * 2;// * 2 since I want two matrices actually. a projection matrix and a view matrix
uint bindingPoint = GetNextFreeBindingPoint();// for the sake of this example you can assume this to be 0

uint bufferHandle = gl.GenBuffer();// create the buffer
gl.BindBuffer(BufferTargetARB.UniformBuffer, bufferHandle);// bind it
gl.BufferData(BufferTargetARB.UniformBuffer, bytes, null, BufferUsageARB.StaticDraw);// allocate video memory for the buffer
gl.BindBuffer(BufferTargetARB.UniformBuffer, 0);// unbind it
gl.BindBufferBase(BufferTargetARB.UniformBuffer, bindingPoint , bufferHandle);// bind the buffer to a binding point

uint shaderHandle = CreateShader();
uint uniformBlockIndex = gl.GetUniformBlockIndex(shaderHandle, "camera");
if(uniformBlockIndex == unchecked((uint) -1)) throw new InvalidOperationException(); // will never happen; Do we have a constant for this somewhere?
gl.UniformBlockBinding(shaderHandle, uniformBlockIndex, bindingPoint);// bind the shaders uniform block to the binding point



Matrix4x4 viewMatrix = GetViewMatrix();
Matrix4x4 projectionMatrix = GetProjectionMatrix();
// TODO - put these matrices into the buffer
// THIS DOES NOT WORK AS INTENDED
gl.BindBuffer(BufferTargetARB.UniformBuffer, bufferHandle);// bind the uniform buffer
unsafe {
    gl.BufferSubData(BufferTargetARB.UniformBuffer, 0, matrixSize, &viewMatrix);
    gl.BufferSubData(BufferTargetARB.UniformBuffer, matrixSize, matrixSize, &projectionMatrix);
}
gl.BindBuffer(BufferTargetARB.UniformBuffer, 0);// unbind it

Following could be an example vertex shader. For the sake of this example, there is no model matrix, texture or lighting involved.

#version 440

layout (location = 0) in vec3 vPos;

layout (std140) uniform camera {
    mat4 viewMatrix;
    mat4 projectionMatrix;
};

void main() {
    gl_Position = projectionMatrix * viewMatrix * vec4(vPos, 1);
}

Thank you very much for your time and thoughts in advance!

[Abrynos]

The problem was not the code, but rather that I mixed up the order of projection and view matrix.

In my shader I had the view-matrix before the projection matrix, while in the C# code I set the projection matrix with an offset and the viewmatrix without one. Order matters!