How can i draw multiple cubes at once Without creating objects

[zhu2900000]

Hi~
I found that multiple objects were created and refreshed in real time, with a lot of display latency. If you do not create a class like the following, but maintain multiple lines, the display efficiency will be much improved. Whether drawing a cube provides a relevant method. Or is there another faster way? Thank you.

Without creating objects, draw multiple cubes at once
like this:

data = np.random.normal(size=(1000, 2))
data[0] = -10, -10
data[1] = 10, -10
data[2] = 10, 10
data[3] = -10, 10
data[4] = -10, -10
plot = scene.Line(data, parent=view.scene)

Create a bunch of cubes in the form of multiple objects and update them in real time with low efficiency. Is it possible to draw many lines at once like drawing lines and update them in real time

[djhoese]

https://vispy.org/faq.html#why-is-my-visualization-slower-when-i-add-more-visual-objects

If you have a lot of lines then creating one array with all of the separate lines and providing the connect keyword argument with "segments":

vispy/vispy/visuals/line/line.py

Lines 53 to 61 in 16d8c5b

	connect : str or array
	Determines which vertices are connected by lines.
	* "strip" causes the line to be drawn with each vertex
	connected to the next.
	* "segments" causes each pair of vertices to draw an
	independent line segment
	* numpy arrays specify the exact set of segment pairs to
	connect.

will give you the best performance. There are a few other options, but in general as the FAQ answer above says, you want to reduce the overall number of Visuals.

[zhu2900000]

https://vispy.org/faq.html#why-is-my-visualization-slower-when-i-add-more-visual-objects

If you have a lot of lines then creating one array with all of the separate lines and providing the connect keyword argument with "segments":

vispy/vispy/visuals/line/line.py

Lines 53 to 61 in 16d8c5b

	connect : str or array
	Determines which vertices are connected by lines.
	* "strip" causes the line to be drawn with each vertex
	connected to the next.
	* "segments" causes each pair of vertices to draw an
	independent line segment
	* numpy arrays specify the exact set of segment pairs to
	connect.

will give you the best performance. There are a few other options, but in general as the FAQ answer above says, you want to reduce the overall number of Visuals.

I can now draw a lot of lines using this method, which works. But I need to draw a lot of cubes now, using a similar method.

[djhoese]

@brisvag has some PRs that would allow instanced drawing (low-level OpenGL feature that allows drawing a lot of the same mesh very quickly). However, for a cube, you probably want to create a single MeshVisual with all of the cubes defined in a series of vertices/faces. @brisvag may even have an example that doesn't require his in-development stuff and can work on existing VisPy.

[brisvag]

It depends how many cubes you have and how they change between each other... Without instanced rendering, each use case must have an ad hoc shader.

If the number of cubes is not crazy (the mesh fits in gpu memory even copied N times) then you can just do everything in the shader; otherwise you need instanced rendering or other clever tricks. Some more code and a more detailed explanation of your needs would be helpful here @zhu2900000 :)

[zhu2900000]

@brisvag

I just wish there were some simple cubes, the number of cubes is plentiful, and write to update it in real time (pan and rotate). Creating a box object for each cube runs like a stutter. My computer doesn't have GPUs.

for i in range(***):
     box3d = scene.visuals.Box(self.size[0],self.size[1],self.size[2],
                                              edge_color="white",parent=self.parent_node)
     self.boxes.append(box3d)

tf = MatrixTransform()
tf.rotate(tf_theta, [0, 0, 1])
tf.scale([tf_width, tf_length, tf_height])
tf.translate((tf_x, tf_y, tf_z))

[brisvag]

Do you create new cubes every time you update? If so, updating them inplace might improve your performance. On the other hand, this seems like the perfect candidate for instanced rendering... Unfortunately, as @djhoese mentioned, this is not yet merged in main, let alone released. However, if you think you can dive in it, feel free to play with it! You can simply check out the branch in #2378, and look at the new instanced cube example I have there :)

[djhoese]

I could have sworn we had an example of this but I can't find it. Can't you make a single MeshVisual with the vertices/faces for many separate "objects"? It might be annoying to construct those initial arrays, but shouldn't that work?

[brisvag]

Yes, that should work as well, but you either need to do everything in python to construct the mesh, or you need to use geometry shaders.

[djhoese]

Right, that's what I meant. In python construct all the mesh vertices and create one MeshVisual representing multiple "objects" in the visualization.