Occlusion of shapes in 3D Mode

[arihantparsoya]

In P3D mode, the shapes are not occluded according to their depth in the scene.

For example, wen rendering the cone:
To Reproduce

from p5 import *

def setup():
	size(640, 360)
	background(204)

def draw():
	background(205, 102, 94)
	rotate_x(frame_count * 0.01)
	rotate_y(frame_count * 0.01)
	cone(40, 70)

run(mode="P3D")

All the triangles of the geometry are seen. the triangles closer to the camera are not occluding the triangles farther from the camera.

[tushar5526]

Are we drawing triangles on both the sides of a face(one on the side which is facing the user one on the side which is not facing the user ) ? Or only the outer triangle (the one which is facing the user)

[arihantparsoya]

@tushar5526 , once the cone is tessellated into smaller triangles (https://github.com/p5py/p5/blob/master/p5/core/primitives3d.py#L348), all the triangles are sent to OpenGL for rendering (https://github.com/p5py/p5/blob/master/p5/sketch/renderer3d.py#L200). The problem is that, OpenGL is unable to use the depth of each triangle in the scene while rendering them correctly. Checkout Z-buffering: https://en.wikipedia.org/wiki/Z-buffering

[ziyaointl]

I managed to make some progress on this by explictly initializing the depth buffer.
However, z-fighting seems pretty bad. May need to make some modifications on how the lines are drawn.

[ziyaointl]

After poking around some more, I realized that the default depth_func is 'less'. Since the lines are always drawn after the triangles, changing the depth_func to 'lequal' alleviates z-fighting quite a bit. There is still some left though... I shall look into transforming the lines towards the camera for an epsilon amount and check if that looks better.

[ziyaointl]

Here are the results of transforming all line objects towards the camera before rendering:

Transformation used:

inv(self.lookat_matrix).dot(translation_matrix(0, 0, Z_EPSILON).dot(self.lookat_matrix))

• Z_EPSILON = 0 (i.e. do nothing)
  

• Z_EPSILON = 0.5
  

• Z_EPSILON = 1.0
  

• Z_EPSILON = 1.5
  

• Z_EPSILON = 2.0
  

• Z_EPSILON = 100
  

Z_EPSILON = 2.0 looks best to me using the default camera. I'll open a PR with this set to 2.