lightposition behaves weirdly

lightposition behaves similarly for both mesh3d and surface, but it’s nearly unusable. Generally x is left (-) to right (+) and y is bottom (-) to top(+), but z has effects that defy easy categorization other than z=1 being “special”. Sometimes x and y flip randomly, and anyway they don’t seem to have the same scales, ie x=y does not put the light at 45 degrees.

[alexcjohnson]

flatshading definitely helps - in fact without it I can’t really figure out any physical meaning to the lighting of mesh3d traces, but with it there does seem to be, for any given lightposition, a light that looks like it’s coming from somewhere fixed wrt the scene as the scene is rotated. And moreover that fixed somewhere is the same for all traces. So based on that alone I’d probably enable flatshading by default. And I’m highly in favor of standardizing all the lightposition defaults to something with intelligible consequences, with all traces matching each other. In fact, can we add a scene.lightposition that all the traces in a scene inherit from if not provided at the trace level?

Now, as to where this light appears to be, my description above still seems to hold. I’d add that when both x and y are fairly small (±hundreds or less) or when z is significant (<-10 or >1) it no longer seems possible to assign the light a fixed position as the scene rotates - I can align the cubes or saddle surfaces in what should be symmetric viewpoints (90-degree rotations of the cube, 180-degree rotations of the saddle) and I get different light regions.

So I definitely would not close this issue. To me this would be closed when the meaning of lightposition.x/y/z can be precisely defined, something like:

x is the position of the light source left (-) or right (+) in screen-space relative to the center of the scene. y is its position below (-) or above(+), and z is its position behind (-) or in front of (+) the screen. Only the normalized x, y, z vector matters, the light always behaves as if it is coming from a point source infinitely far away.

I don’t mind waiting on this - doesn’t seem like we have anyone who particularly cares about this. But it’s definitely still a bug.

Here's the dash app I'm using to play with this, based on your codepen @archmoj, plus sliders for `lightposition.x/y/z`. It's actually quite responsive, even though I'm sending the whole figure up with every mousemove. Go `Plotly.react`!

import dash
import dash_html_components as html
import dash_core_components as dcc
from dash.dependencies import Input, Output


app = dash.Dash(__name__)


app.layout = html.Div([
    html.Div([
        html.P(id='xout'),
        dcc.Slider(id='x', value=1000, min=-10000, max=10000, updatemode='drag'),
        html.P(id='yout'),
        dcc.Slider(id='y', value=1000, min=-10000, max=10000, updatemode='drag'),
        html.P(id='zout'),
        dcc.Slider(id='z', value=0, min=-100, max=100, updatemode='drag'),
    ]),
    dcc.Graph(id='fig')
])


@app.callback(
    [
        Output('xout', 'children'),
        Output('yout', 'children'),
        Output('zout', 'children'),
        Output('fig', 'figure')
    ],
    [Input('x', 'value'), Input('y', 'value'), Input('z', 'value')]
)
def fig(x, y, z):
    camera1 = {"eye": {"x": 1.2, "y": 1.2, "z": 1.2}}
    camera2 = {"eye": {"x": 1, "y": 2, "z": 1}}

    lightposition = {"x": x, "y": y, "z": z}
    color = "yellow"
    return 'x: {}'.format(x), 'y: {}'.format(y), 'z: {}'.format(z), {
      "data":  [{
        "x": [0, 1, 0, 1, 0, 1, 0, 1],
        "y": [0, 0, 1, 1, 0, 0, 1, 1],
        "z": [0, 0, 0, 0, 1, 1, 1, 1],
        "i": [0, 3, 4, 7, 0, 6, 1, 7, 0, 5, 2, 7],
        "j": [1, 2, 5, 6, 2, 4, 3, 5, 4, 1, 6, 3],
        "k": [3, 0, 7, 4, 6, 0, 7, 1, 5, 0, 7, 2],
        "flatshading": True,
        "lightposition": lightposition,
        "color": color,
        "type": "mesh3d",
        "scene": "scene1"
      }, {
        "x": [0, 1, 0, 1, 0, 1, 0, 1],
        "y": [0, 0, 1, 1, 0, 0, 1, 1],
        "z": [0, 0, 0, 0, 1, 1, 1, 1],
        "i": [0, 3, 4, 7, 0, 6, 1, 7, 0, 5, 2, 7],
        "j": [1, 2, 5, 6, 2, 4, 3, 5, 4, 1, 6, 3],
        "k": [3, 0, 7, 4, 6, 0, 7, 1, 5, 0, 7, 2],
        "flatshading": True,
        "lightposition": lightposition,
        "color": color,
        "type": "mesh3d",
        "scene": "scene2"
      }, {
        "x": [0, 1],
        "y": [0, 1],
        "z": [[0, 1], [1, 0]],
        "lightposition": lightposition,
        "colorscale": [[0, color], [1, color]],
        "showscale": False,
        "type": "surface",
        "scene": "scene3"
      }, {
        "x": [0, 1],
        "y": [0, 1],
        "z": [[0, 1], [1, 0]],
        "lightposition": lightposition,
        "colorscale": [[0, color], [1, color]],
        "showscale": False,
        "type": "surface",
        "scene": "scene4"
      }, {
        "x": [0, 0, 1, 1, 0, 0, 1, 1],
        "y": [0, 1, 1, 0, 0, 1, 1, 0],
        "z": [0, 0, 0, 0, 1, 1, 1, 1],
        "u": [0, 0, 1, 1, 0, 0, 1, 1],
        "v": [0, 1, 1, 0, 0, 1, 1, 0],
        "w": [0, 0, 0, 0, 1, 1, 1, 1],
        "lightposition": lightposition,
        "colorscale": [[0, color], [1, color]],
        "showscale": False,
        "type": "cone",
        "scene": "scene5"
      }, {
        "x": [0, 0, 1, 1, 0, 0, 1, 1],
        "y": [0, 1, 1, 0, 0, 1, 1, 0],
        "z": [0, 0, 0, 0, 1, 1, 1, 1],
        "u": [0, 0, 1, 1, 0, 0, 1, 1],
        "v": [0, 1, 1, 0, 0, 1, 1, 0],
        "w": [0, 0, 0, 0, 1, 1, 1, 1],
        "lightposition": lightposition,
        "colorscale": [[0, color], [1, color]],
        "showscale": False,
        "type": "cone",
        "scene": "scene6"
      }, {
        "x": [0, 0, 1, 1, 0, 0, 1, 1],
        "y": [0, 1, 1, 0, 0, 1, 1, 0],
        "z": [0, 0, 0, 0, 1, 1, 1, 1],
        "u": [0, 0, 1, 1, 0, 0, 1, 1],
        "v": [0, 1, 1, 0, 0, 1, 1, 0],
        "w": [0, 0, 0, 0, 1, 1, 1, 1],
        "lightposition": lightposition,
        "colorscale": [[0, color], [1, color]],
        "showscale": False,
        "type": "streamtube",
        "scene": "scene7"
      }, {
        "x": [0, 0, 1, 1, 0, 0, 1, 1],
        "y": [0, 1, 1, 0, 0, 1, 1, 0],
        "z": [0, 0, 0, 0, 1, 1, 1, 1],
        "u": [0, 0, 1, 1, 0, 0, 1, 1],
        "v": [0, 1, 1, 0, 0, 1, 1, 0],
        "w": [0, 0, 0, 0, 1, 1, 1, 1],
        "lightposition": lightposition,
        "colorscale": [[0, color], [1, color]],
        "showscale": False,
        "type": "streamtube",
        "scene": "scene8"
      }],
      "layout": {
        "paper_bgcolor": "lightblue",
        "uirevision": True,
        "width": 1200,
        "height": 600,
        "scene1": {
          "domain": {
            "x": [0, 0.25],
            "y": [0, 0.25]
          },
          "camera": camera1
        },
        "scene2": {
          "domain": {
            "x": [0, 0.25],
            "y": [0.5, 1]
          },
          "camera": camera2
        },
        "scene3": {
          "domain": {
            "x": [0.25, 0.5],
            "y": [0, 0.5]
          },
          "camera": camera1
        },
        "scene4": {
          "domain": {
            "x": [0.25, 0.5],
            "y": [0.5, 1]
          },
          "camera": camera2
        },
        "scene5": {
          "domain": {
            "x": [0.5, 0.75],
            "y": [0, 0.5]
          },
          "camera": camera1
        },
        "scene6": {
          "domain": {
            "x": [0.5, 0.75],
            "y": [0.5, 1]
          },
          "camera": camera2
        },
        "scene7": {
          "domain": {
            "x": [0.75, 1],
            "y": [0, 0.5]
          },
          "camera": camera1
        },
        "scene8": {
          "domain": {
            "x": [0.75, 1],
            "y": [0.5, 1]
          },
          "camera": camera2
        }
      }
    }


if __name__ == '__main__':
    app.run_server(debug=True)

[aniruddhkb]

Further, it seems that there is some degree of control available to the light’s position in Z, but I don’t see any change in X, Y