Reply To: Tris to Quads: Shape Angle

[fabianm]

I wanted to know this as well and since I couldn’t find more info than you did I examined the code itself. Blender Github file

You are correct that the “Face Angle” parameter is compared with the dot product of the normal vectors of the two triangles (the angle between them).

if (delimit_data->do_angle_face) {
    if (dot_v3v3(f_a->no, f_b->no) < delimit_data->angle_face__cos) {
        goto fail;
    }
}

  

The “Angle Shape” parameter means, that two triangles are only merged into a quad if 

|interior_angle - 90°| <= shape_angle

holds true for all 4 interior angles of the resulting quad.
The value is basically a measure for how much the resulting quad can differ from a rectangle.
(As the docs say: With a shape angle of 0°, only triangles are merged that form a rectangle)

This is the code (The condition is the inverse of the above because it’s written as a fail condition):

if (
(fabsf(angle_normalized_v3v3(edge_vecs[0], edge_vecs[1]) - (float)M_PI_2) > delimit_data->angle_shape) ||
(fabsf(angle_normalized_v3v3(edge_vecs[1], edge_vecs[2]) - (float)M_PI_2) > delimit_data->angle_shape) ||
(fabsf(angle_normalized_v3v3(edge_vecs[2], edge_vecs[3]) - (float)M_PI_2) > delimit_data->angle_shape) ||
(fabsf(angle_normalized_v3v3(edge_vecs[3], edge_vecs[0]) - (float)M_PI_2) > delimit_data->angle_shape))
        {
          goto fail;
        }

Two more pictures to illustrate this: