OpenTK - Model view projection problems

Question

I have been following the C++ OpenGL Matrices Tutorial and attempting to translate it into C# OpenTK, without using a MVP matrix I get a red triangle drawn on screen but whenever I try to use it I get nothing draw or at least a connot SEE anything being drawn, no matter where I try to place the camera.

There are code snippets below but you can view the whole source code here

This is the C# code to build the MVP Matrix

/Attempt to build our model view projection matrix

//We use an Identity matrix for the model
Matrix4 _model = Matrix4.Identity;

Matrix4 _projection = Matrix4.CreatePerspectiveFieldOfView(1.0f, 4.0f / 3.0f, 0.1f, 100.0f);

//Camera will be as 4,3,3 looking at origin, and set up direction to 1
Matrix4 _view = Matrix4.LookAt(new Vector3(4,3,3), new Vector3(0,0,0), new Vector3(0,1,0));

//combine into our model view projection
Matrix4 _model_view_projection = _projection * _view * _model;

Then we pass this matrix into the vertex shader, the vPosition element are vec3 vertices passed from the C# code

#version 330

uniform mat4 viewProjection;

in vec3 vPosition;

void main()
{
    //This line doesn't work
    gl_Position = viewProjection * vec4(vPosition, 1);

    //This line works
    //gl_Position = vec4(vPosition, 1);
}

How you pass the Matrix to the shader?Sometimes it is better to pass them one after one and combine them in your vertex shader — greedsin
And your view Matrix has an angle of 1 ,you maybe set it between 45 and 60 — greedsin
@lolio Will try that. Also, the fov parameter is in radians so 1.0f is roughly 60 degrees — Tom Gothorp

Alex Green Alex Green · Accepted Answer · 2016-02-11T20:51:57

Error in code:

Matrix4 _model_view_projection = _projection * _view * _model;

Must be:

Matrix4 _model_view_projection = _model * _view * _projection;
// For OpenTK, Pencil.Gaming ...

That's because OpenTK use row-major matrices (they are transposed). In C# you must multiply matrices in this way (not in the shaders).

OpenTK - Model view projection problems

1 Answers