[fpc-pascal] GLM library alternative?

[Marco van de Voort]

In our previous episode, Ryan Joseph said:
> > On May 28, 2017, at 10:33 PM, Ryan Joseph <ryan at thealchemistguild.com> wrote:
> > 
> > 	projTransform := TMatrix4x4.CreatePerspective(60.0, 500 / 500, 0.1, 10.0);
> > 	modelTransform := TMatrix4x4.CreateTranslation(0, 0, -3.0) * TMat4.CreateRotateX(54);
> 
> I found out the problem. I was expecting the multiply to work like with GLM where you could do: 
> 
> translation * rotation
> 
> but with the operator overloads I need to do protation * translation.
> Anthony?s multiply matrix 4 operators did this in the order I expected and
> how I figured it out.  Not sure why and it?s probably not safe to swap the
> parameters because it would likely break other parts of the unit.

For the 2Ders, in old GL I used glortho2d a lot. In newer ones I missed that, but I found
an equivalent on stackoverflow:

// http://stackoverflow.com/questions/21323743/modern-equivalent-of-gluortho2d
procedure MyOrtho2D(var mat : TGLMatrixf4;left,right,bottom,top:single);
var inv_y,inv_x : single;
begin
      inv_y := 1.0 / (top - bottom);
      inv_x := 1.0 / (right - left);

    // this is basically from
    // http://en.wikipedia.org/wiki/Orthographic_projection_(geometry)

    //first column
    mat[0][0] := (2.0*inv_x);
    mat[0][1] := (0.0);
    mat[0][2] := (0.0);
    mat[0][3] := (0.0);

    //second
    mat[1][0] := (0.0);
    mat[1][1] := (2.0*inv_y);
    mat[1][2] := (0.0);
    mat[1][3] := (0.0);

    //third
    mat[2][0] :=  (0.0);
    mat[2][1] :=  (0.0);
    mat[2][2] :=  (-2.0*inv_z);
    mat[2][3] :=  (0.0);

    //fourth
    mat[3][0] :=  (-(right + left)*inv_x);
    mat[3][1] :=  (-(top + bottom)*inv_y);
    mat[3][2] :=  (-(zFar + zNear)*inv_z);
    mat[3][3] :=  (1.0);
end;

I have a TGLvector for zoom (X/Y) and one for pan (offset, also in X and Y
direction).

// calcs a matrix for the shader. pass the matrix as an uniform and multiply  in vertex or geometry shader

procedure myorthohelp(var mat : TGLMatrixf4;const
aoffs,azoom:TGLVectorf2;topdown:boolean=false);
begin
  myOrtho2D(mat,aoffs[0], 1.0 / (aZoom[0]) + (aoffs[0]), 1.0 / (aZoom[1]) + (aoffs[1]), aoffs[1])
end;