Maintain FOV

[t-mat]

Currently, we get different field of view (FOV) image when we set -width and -height. So when increase resolution, almost all rays go straight to sky or ground. And amount of computation is not increase properly.

Following change resolve this problem :

// original
dir := t.Scale(-1)
    .Add(
        a.Scale(rnd(seed) + float64(x))
        .Add(b.Scale(float64(r) + rnd(seed)))
        .Add(c)
        .Scale(16)
    ).Normalize()

// modified
dir := t.Scale(-1)
    .Add(
        a.Scale(rnd(seed) + float64(x*512) / float64(*width))
        .Add(b.Scale(float64(r*512) / float64(*height) + rnd(seed)))
        .Add(c)
        .Scale(16)
    ).Normalize()

This solution make different problem

• Break compatibility with old benchmarks
• Break aspect ratio

[kidoman]

This is definitely something I have been thinking about. To make the higher resolution benchmarks "effective" we need to be able to scale the rendered "image" along with the image size

[kidoman]

I have implemented some changes in the Go version. Will need to port these over to the other programs. Thanks for finding the fix