[PATCH] cliptest: Don't underrun the vertex array of empty polygons.

[Pekka Paalanen]

On Tue, 19 Aug 2014 13:10:55 +0200
Ondřej Majerech <oxyd.oxyd at gmail.com> wrote:

> This silences the following warning:
> 
>   clients/cliptest.c:277:22: warning: array subscript is below array
>   bounds [-Warray-bounds]
>     ctx->prev.x = src->x[src->n - 1];

Hi,

seems like I would need something more recent than gcc 4.6.4 to get
these warnings, right?

Do you not get these warnings from src/vertex-clipping.c too?

At minimum, could you patch both clients/cliptest.c and
src/vertex-clipping.c in the same patch, and check that the duplicated
code is identical.

An even better alternative would be to just drop the duplicate code
from cliptest.c, and make it somehow just use src/vertex-clipping.c
and .h. I'm not sure how the build system would cope with that, but
that would be excellent. So first remove duplication, then fix the
issues.

Also, I think the correct condition would be:
	if (src->n < 2)
		return 0;

Because if a polygon has less than 2 points, it's not a polygon that
could even theoretically be clipped. The 2 points case also is
denegerate, but least it has two lines that can be clipped.


Thanks,
pq

> 
> Signed-off-by: Ondřej Majerech <oxyd.oxyd at gmail.com>
> ---
>  clients/cliptest.c | 12 ++++++++++++
>  1 file changed, 12 insertions(+)
> 
> diff --git a/clients/cliptest.c b/clients/cliptest.c
> index 907c5d4..20b3776 100644
> --- a/clients/cliptest.c
> +++ b/clients/cliptest.c
> @@ -287,6 +287,9 @@ clip_polygon_left(struct clip_context *ctx, const struct polygon8 *src,
>  	enum path_transition trans;
>  	int i;
>  
> +	if (src->n == 0)
> +		return 0;
> +
>  	clip_context_prepare(ctx, src, dst_x, dst_y);
>  	for (i = 0; i < src->n; i++) {
>  		trans = path_transition_left_edge(ctx, src->x[i], src->y[i]);
> @@ -303,6 +306,9 @@ clip_polygon_right(struct clip_context *ctx, const struct polygon8 *src,
>  	enum path_transition trans;
>  	int i;
>  
> +	if (src->n == 0)
> +		return 0;
> +
>  	clip_context_prepare(ctx, src, dst_x, dst_y);
>  	for (i = 0; i < src->n; i++) {
>  		trans = path_transition_right_edge(ctx, src->x[i], src->y[i]);
> @@ -319,6 +325,9 @@ clip_polygon_top(struct clip_context *ctx, const struct polygon8 *src,
>  	enum path_transition trans;
>  	int i;
>  
> +	if (src->n == 0)
> +		return 0;
> +
>  	clip_context_prepare(ctx, src, dst_x, dst_y);
>  	for (i = 0; i < src->n; i++) {
>  		trans = path_transition_top_edge(ctx, src->x[i], src->y[i]);
> @@ -335,6 +344,9 @@ clip_polygon_bottom(struct clip_context *ctx, const struct polygon8 *src,
>  	enum path_transition trans;
>  	int i;
>  
> +	if (src->n == 0)
> +		return 0;
> +
>  	clip_context_prepare(ctx, src, dst_x, dst_y);
>  	for (i = 0; i < src->n; i++) {
>  		trans = path_transition_bottom_edge(ctx, src->x[i], src->y[i]);