tinyrenderer | A brief computer graphics / rendering course | Graphics library

I wrote a program that takes in entry some points, expressed in 3D coordinates and that must be drawn in a 2D canvas. I use perspective projection, homogeneous coordinates and similar triangles to do that. However, my program does not work and I actually don't know why.

I followed two tutorials. I really understood the geometrical definitions and properties I have read. However, my implementation fails... I will write references to these both courses little by little, to make your reading more confortable :).

The perspective projection is done following this workflow (cf. these 2 courses - I wrote pertinent links (HTML anchors) further down, in this post) :

1. Definition of the points to draw, expressed according to the world's coordinates system ; Definition of the matrix of projection, which is a matrix of transformation that "converts" a point expressed according to the world coordinates system into a point expressed according to the camera's coordinates system (NB : this matrix also can be understood as being the camera)

2. Product of these points with this matrix (as defined in the adequat part, below) : the product these points results in the conversion of these points to the camera's coordinates system. Note that points and matrix are expressed in 4D (concept of homogenous coordinates).

3. Use of similar triangles concept to project (only computing is done at this step) on the canvas the in-camera-expressed points (using their 4D coordinates) : they are now expressed in 3D (the third coordinate is computed but not actually used on the canvas)

4. Last step : rasterization, to actually draw the pixels on the canvas (other computing AND displaying are done at this step).

Well, I want to draw a cube but it doesn't appear. The projected points seem to be drawn on the same coordinates.

Instead of my cube, only one black pixel is visible.

NB : since X11 is not activated on Scastie, the window I want to create won't be shown.

https://scastie.scala-lang.org/2LQ1wSMBTWqQQ7hql35sOg

Perhaps the problem is bound to the entries ? Well, I give you them.

Ref. : myself