elm-3d-camera

This package is provides convenient ways to define and use perspective and orthographic cameras in 3D. It is based on elm-geometry and has two main goals:

• Provide a way to construct WebGL model/view/projection matrices that is more intuitive than using elm-community/linear-algebra directly
• Provide standalone 3D-to-2D projection functionality that can be used outside of WebGL

Defining cameras

To define a camera, you first create a viewpoint which represents the position and orientation of the camera:

cameraViewpoint =
    Viewpoint3d.lookAt
        { eyePoint = Point3d.fromCoordinates ( 10, 0, 5 )
        , focalPoint = Point3d.origin
        , upDirection = Direction3d.positiveZ
        }

You can then create either a perspective or orthographic camera from the viewpoint:

perspectiveCamera =
    Camera3d.perspective
        { viewpoint = cameraViewpoint
        , verticalFieldOfView = degrees 30
        , nearClipDistance = 0.1
        , farClipDistance = 1000
        , screenWidth = 1024
        , screenHeight = 768
        }

orthographicCamera =
    Camera3d.orthographic
        { viewpoint = cameraViewpoint
        , viewportHeight = 5
        , nearClipDistance = 0.1
        , farClipDistance = 1000
        , screenWidth = 1024
        , screenHeight = 768
        }

WebGL rendering

Once you have a camera, you can use it to get WebGL model/view/projection matrices:

projectionMatrix =
    Camera.projectionMatrix camera

viewMatrix =
    Camera.viewMatrix camera

modelViewProjectionMatrix =
    Camera3d.modelViewProjectionMatrix modelFrame camera

(In the final example, the position and orientation of the object to be rendered is defined by an elm-geometry Frame3d value.)

Projection to screen space

You can also use a Camera3d to project points, lines, triangles and polylines from 3D to 2D:

import Point3d.Projection as Point3d
import LineSegment3d.Projection as LineSegment3d

point2d =
    point3d |> Point3d.toScreenSpace camera

lineSegment2d =
    lineSegment3d |> LineSegment3d.toScreenSpace camera

This allows you to, for example, do a perspective projection of 3D points and lines into 2D so that those points and lines can be rendered with SVG (taking advantage of SVG features like perfect circles and dashed lines which are difficult to do with WebGL):

Roadmap

Several more features are planned:

• More Viewpoint3d constructors other than just lookAt
• More 3D-to-2D projections (directions, axes)
• Construction of 3D pick rays and cut planes from 2D screen points and lines

Questions? Comments?

Please open a new issue if you run into a bug, if any documentation is missing/incorrect/confusing, or if there's a new feature that you would find useful. For general questions about using elm-3d-camera, try:

• Joining the #geometry or #webgl channels on the Elm Slack, or sending me (@ianmackenzie) a message - even if you don't have any particular questions right now, it would be great to know what you're hoping to do with the package!
• Posting to the Elm Discourse forums
• Or if you happen to be in the New York area, come on out to the Elm NYC meetup =)

You can also find me on Twitter (@ianemackenzie), where I occasionally post elm-geometry-related stuff like demos or new releases. Have fun, and don't be afraid to ask for help!