I tried to implement my own perspective matrix and it doesn't work. I don't understand why. With just with my view matrix (without Perspective Matrix) I can see my mesh.

Here my view matrix :

Vec3f position(0.0,0.0,-5.0);
Vec3f target(0.0,0.0,0.0);

Mat4f Camera::LookAt(Vec3f target, Vec3f position)
 //ce dont j'ai besoin pour calculer les parametre de ma camera...
 Vec3f up_world = Vec3f(0.0,1.0,0.0);
 Vec3f forward = (position - target).normalize();
 Vec3f right = up_world.cross(forward).normalize();
 Vec3f up = forward.cross(right).normalize();

 Mat3f R;


 Mat4f R4(R);

 Vec3f mp = position * -1.0f;
 Mat4f P4;

 _LookAt = R4 *P4;
 return  _LookAt;

And my Perspective Matrix :

Mat4f Camera::perspective(float fovy, float aspect, float zNear, float zFar)

  float theta = fovy * 0.5f * (180.f / M_PI);
  float range = zFar - zNear;
  float invtan = 1.f/tanf(theta);

  Mat4f projMat(invtan / aspect,  0.0f,    0.0f,                       0.0f,
                           0.0f,  invtan,  0.0f,                       0.0f,
                           0.0f,  0.0f,    -(zFar + zNear) / range,  -2 * zNear * zFar / range,
                           0.0f,  0.0f,    -1.0f,                      0.0f);

    _perspectiveCam = projMat;
    std::cout << _perspectiveCam << std::endl;
    return _perspectiveCam;

  Mat4f perspective(float fovy = M_PI/2, float aspect = (1280.f/720.f)*1.f, float zNear = 0.1f, float zFar = 100.f);

My shader is very simple so it can't be the problem..

#version 410 core

layout(location = 0) in vec3 V_position;
layout(location = 1) in vec3 V_color;
layout(location = 2) in vec3 V_normal;

uniform mat4 view_matrix;
uniform mat4 proj_matrix;

out vec3 color;
void main()
    color = V_color;
    gl_Position = proj_matrix * view_matrix * vec4(V_position, 1.);

when I initialise _perspectiveCam with the unit matrix 4x4 it displays my triangle.. but when I implement _perspectiveCam like in the function it does not display my triangle

Here my Set col function :

template <typename TYPE>
void Mat4<TYPE>::setCol(int i, Vec4<TYPE>& vec4)
  for (size_t k = 0; k < 4; k++)
    setElement(k,i, vec4.getElement(k));


void setElement(int i,int j, TYPE var){element[i*4 + j] = var;}
TYPE getElement(int i, int j) const {return element[i*4 + j];}
  • 2
    \$\begingroup\$ Welcome to GDSE. I suggest editing to include the shader as well. Even simple code can hide errors. And if it is simple, it won't take much room. \$\endgroup\$ – Pikalek Nov 23 '18 at 16:09
  • \$\begingroup\$ My long and bitter experience tells me: everytime somebody says "it can't be the problem" - it turns out to actually be the problem. So yes, you should post your shader too. \$\endgroup\$ – Maximus Minimus Nov 23 '18 at 17:16
  • \$\begingroup\$ haha maybe, sorry for my late response i did not have connection i will edit my post with the shader \$\endgroup\$ – Soof Benzaii Nov 25 '18 at 9:30

First off: "It doesn't work" is not very descriptive. What are you observing? A black screen? Distorted geometry?

Next: What is the convention for your Mat4f class? Can you show setCol() implementation? Is your translation part stored in [3],[7],[11] or [12],[13],[14]?

Because I suspect that your projmat may have flipped col/row?

In my implementation, the projmat (same values as yours) is laid out differently, like so:

    mout[0] = f / aspect;
    mout[1] = 0.0f;
    mout[2] = 0.0f;
    mout[3] = 0.0f;

    mout[4] = 0.0f;
    mout[5] = f;
    mout[6] = 0.0f;
    mout[7] = 0.0f;

    mout[8] = 0.0f;
    mout[9] = 0.0f;
    mout[10] = (zFar+zNear) / (zNear-zFar);
    mout[11] = -1.0f;

    mout[12] = 0.0f;
    mout[13] = 0.0f;
    mout[14] = 2 * zFar * zNear /  (zNear-zFar);
    mout[15] = 0.0f;

And after doing proj * view * model, I feed it into the shader with glUniformMatrix4fv().

In my shader, I post-multiply the position, like so:

gl_Position = modelcamviewprojmat * position;

My matrix class has translation in [12], [13], [14]

The things I would try:

  1. Switch multiplication order, to see if it helps: sometimes it is model * view * proj, sometimes it is proj * view * model.
  2. Make sure the layout of your proj matrix, above, is correct.
  • \$\begingroup\$ Thank you for your answer, i have forgotten to transpose my lookAt and perspective Matrix.. I thought Open GL works with column major matrix but apparently it 's not the case .. So thank you \$\endgroup\$ – Soof Benzaii Nov 26 '18 at 10:24

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