[vlc-devel] [PATCH 11/18] input: use vlc_viewpoint_from/to_euler

[Steve Lhomme]

On 2021-03-31 11:25, Alexandre Janniaux wrote:
> From: Alexandre Janniaux <alexandre.janniaux at gmail.com>
> 
> ... and also clip pitch to avoid singularities in locations where a

It looks like a commit title that was cut by GitHub.

> relative viewpoint update is used. Otherwise, conversions between
> viewpoints and euler angles might lead to corrupted values and blinking
> pitch angles.
> ---
>   src/input/input.c | 22 ++++++++++++++++++----
>   1 file changed, 18 insertions(+), 4 deletions(-)
> 
> diff --git a/src/input/input.c b/src/input/input.c
> index 69552bc3e5..b134d4f097 100644
> --- a/src/input/input.c
> +++ b/src/input/input.c
> @@ -1758,6 +1758,10 @@ static void ControlNav( input_thread_t *p_input, int i_type )
>   
>       if( b_viewpoint_ch && viewpoint_updated )
>       {
> +        /* We need to clip the pitch here to avoid singularity poles, otherwise
> +         * the next vlc_viewpoint_to_euler might reverse the pitch. */
> +        pitch = VLC_CLIP(pitch, -85.f, 85.f);

These arbitrary values should have a name. And why not use -90, 90 ? In 
Matroska you can have pitch values of -90 to 90, both included. Same for 
MP4 [1]. Does a pitch of 270 turns to 85 ?

[1] 
https://github.com/google/spatial-media/blob/master/docs/spherical-video-v2-rfc.md

> +
>           priv->viewpoint_changed = true;
>           vlc_viewpoint_from_euler( &priv->viewpoint, yaw, pitch, roll );
>           ViewpointApply( p_input );
> @@ -2148,10 +2152,20 @@ static bool Control( input_thread_t *p_input,
>               else
>               {
>                   priv->viewpoint_changed = true;
> -                priv->viewpoint.yaw   += param.viewpoint.yaw;
> -                priv->viewpoint.pitch += param.viewpoint.pitch;
> -                priv->viewpoint.roll  += param.viewpoint.roll;
> -                priv->viewpoint.fov   += param.viewpoint.fov;
> +                float previous[3], update[3];
> +                vlc_viewpoint_to_euler(&priv->viewpoint, &previous[0],
> +                                       &previous[1], &previous[2]);
> +                vlc_viewpoint_to_euler(&param.viewpoint, &update[0],
> +                                       &update[1], &update[2]);
> +
> +                /* We need to clip the pitch here to avoid singularity poles,
> +                 * otherwise the next vlc_viewpoint_to_euler might reverse
> +                 * the pitch. */
> +                vlc_viewpoint_from_euler(&priv->viewpoint,
> +                        previous[0] + update[0],
> +                        VLC_CLIP(previous[1] + update[1], -85.f, 85.f),
> +                        previous[2] + update[2]);
> +                priv->viewpoint.fov += param.viewpoint.fov;
>               }
>   
>               ViewpointApply( p_input );
> -- 
> 2.31.0
> 
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