Matrices cannot be converted to other matrices

[mfiano]

Varjo: There is no applicable method for the glsl function 'MAT3'
when called with argument types:
(:MAT4)

The OpenGL wiki states:

A matrix can be constructed from another matrix A matrix can only be constructed from a single other matrix. The column and row values from the input matrix are copied to their corresponding values in the output; any values of the output not filled in are filled with the identity matrix.

Therefore:

 mat3 diagMatrix = mat3(5.0);  // Diagonal matrix with 5.0 on the diagonal.
 mat4 otherMatrix = mat4(diagMatrix);
The otherMatrix is a diagonal matrix, where the first 3 values are 5.0, and the last diagonal value is 1.0.

There are no restrictions on size when doing matrix construction from another matrix. So you can construct a 4x2 matrix from a 2x4 matrix; only the corresponding elements are copied.

[mfiano]

This gist addresses issues #205 #206 and #207 if you want to copy/paste and ensure I didn't make any mistakes: https://gist.github.com/mfiano/78628dfa7251aba5aef89d7ac587c791

[cbaggers]

Thanks for the report. Merging these matrix type constructor issues into #209