javascript - Three.js - Orthographic camera

Question

I've working on an app which displays some 3D models. We load the models, create the meshes, add them to the scene...standard procedure. After the last mesh is added, we compute the bounding box in order to move the camera and cover all the scene, using the size of the total geometry and the size of the viewport to do the math.

    if (bounds.bx / bounds.by < camera.aspect) {
        /* Vertical max */
        r = bounds.by / (2 * Math.tan(Math.PI / 8));
    } else {
        /* Horizontal max */
        hFOV = 2 * Math.atan(Math.tan(Math.PI / 8) * camera.aspect);
        r = bounds.bx / (2 * Math.tan((hFOV / 2)));
    }

bounds is an object containing the width and height of the bounding box. After this calculation, we move the camera(plus a little ratio, just aesthetics, we want a little room between the geometry and the screen border :) ) and render

    camera.position.z = r * 1.05;

So far this is implemented and runs ok. This has been done with PerspectiveCamera. Now we want to change that and use OrthographicCamera...turns out to be a mess. Models are too small, we lose the mousewheel zoom from the TrackBall Controls and the algorithm to move the camera is not working anymore. Also I don't understand the parameters of the constructor for the camera...these width and height are for the geometry or the viewport?

Answer 1

The pattern for instantiating an orthographic camera in three.js is:

var camera = new THREE.OrthographicCamera( width / - 2, width / 2, height / 2, height / - 2, near, far );

where width and height are the width and height of the camera's cuboid-shaped frustum measured in world-space units.

near and far are the world-space distances to the near and far planes of the frustum. Both near and far should be greater than zero.

To prevent distortion, you will typically want the aspect ratio of the orthographic camera ( width / height ) to match the aspect ratio of the render's canvas. (see *Note below)

It is unfortunate that many of the three.js examples pass window.innerWidth and window.innerHeight as args to this constructor. Doing so only makes sense if the orthographic camera is used for rendering to a texture, or if the world units for your orthographic scene are in pixels.

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*Note: Actually, the camera aspect ratio should match the aspect ratio of the renderer's viewport. The viewport can be a sub-region of the canvas. If you do not set the renderer's viewport directly using renderer.setViewport(), the viewport will be the same size as the canvas, and hence have the same aspect ratio as the canvas.

three.js r.73