[PATCH weston] Simply the matrix calculation for zooming

[Kristian Høgsberg]

On Fri, Apr 25, 2014 at 01:19:37PM +0100, Neil Roberts wrote:
> In order to apply the zoom transformation to the output matrix, Weston was
> doing the following:
> 
> • Create a temporary matrix to hold the translation
> • Invert the translation matrix using weston_matrix_invert into
>   another temporary matrix
> • Scale that matrix by the scale factor
> • Multiply the current matrix with the temporary matrix
> 
> Using weston_matrix_invert to invert a translation matrix is over the top.
> Instead we can just negate the values we pass to weston_matrix_translate.
> Matrix multiplication is associative so creating a temporary matrix to hold the
> scale and translation transform should be equivalent to just applying them
> directly to the output matrix.

Heh, nice clean up, that always looked like it was too complicated for its
own good.  Patch applied.

Kristian

> ---
>  src/compositor.c | 13 ++++---------
>  1 file changed, 4 insertions(+), 9 deletions(-)
> 
> diff --git a/src/compositor.c b/src/compositor.c
> index fd2decb..f836cf7 100644
> --- a/src/compositor.c
> +++ b/src/compositor.c
> @@ -3186,8 +3186,6 @@ WL_EXPORT void
>  weston_output_update_matrix(struct weston_output *output)
>  {
>  	float magnification;
> -	struct weston_matrix camera;
> -	struct weston_matrix modelview;
>  
>  	weston_matrix_init(&output->matrix);
>  	weston_matrix_translate(&output->matrix,
> @@ -3202,14 +3200,11 @@ weston_output_update_matrix(struct weston_output *output)
>  
>  	if (output->zoom.active) {
>  		magnification = 1 / (1 - output->zoom.spring_z.current);
> -		weston_matrix_init(&camera);
> -		weston_matrix_init(&modelview);
>  		weston_output_update_zoom(output);
> -		weston_matrix_translate(&camera, output->zoom.trans_x,
> -					-output->zoom.trans_y, 0);
> -		weston_matrix_invert(&modelview, &camera);
> -		weston_matrix_scale(&modelview, magnification, magnification, 1.0);
> -		weston_matrix_multiply(&output->matrix, &modelview);
> +		weston_matrix_translate(&output->matrix, -output->zoom.trans_x,
> +					output->zoom.trans_y, 0);
> +		weston_matrix_scale(&output->matrix, magnification,
> +				    magnification, 1.0);
>  	}
>  
>  	output->dirty = 0;
> -- 
> 1.9.0
> 
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