gl-renderer: Set pitch correctly for subsampled textures

zwp_linux_dmabuf_v1 allows clients to pass an explicit pitch for each
plane, but wl_shm only takes a single pitch parameter; the pitch for
secondary planes must be inferred.

Multi-plane sub-sampled textures have partial width/height, e.g.
YUV420/I420 has a full-size Y plane, followed by a half-width/height U
plane, and a half-width/height V plane.

GStreamer's waylandsink - the only user of wl_shm YUV formats - expects
the implementation to follow the example of Xv and implicitly divide the
pitch for secondary planes by the subsampling factor. gl-renderer was
not doing this, and instead just using the (larger) stride provided by
the client for all planes in the buffer.

Fix gl-renderer to divide pitch by the subsampling factor when uploading
from subsampled SHM buffers into GL textures, also dividing co-ordinates
when doing offset partial uploads.

Tested with:
  $ gst-launch-1.0 videotestsrc ! waylandsink

Signed-off-by: Daniel Stone <daniels@collabora.com>
Reported-by: Fabien Lahoudere <fabien.lahoudere@collabora.co.uk>
Tested-by: Fabien Lahoudere <fabien.lahoudere@collabora.co.uk>
Reviewed-by: Arnaud Vrac <avrac@freebox.fr>
Acked-by: Vincent ABRIOU <vincent.abriou@st.com>
Acked-by: Nicolas Dufresne <nicolas.dufresne@collabora.com>
Acked-by: Pekka Paalanen <pekka.paalanen@collabora.co.uk>
Fixes: fdeefe4241 ("gl-renderer: add support of WL_SHM_FORMAT_YUV420")
Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=103063

libweston/gl-renderer.c

@@ -1445,14 +1445,14 @@ gl_renderer_flush_damage(struct weston_surface *surface)
 		goto done;
 	}
 
-	glPixelStorei(GL_UNPACK_ROW_LENGTH_EXT, gs->pitch);
-
 	if (gs->needs_full_upload) {
 		glPixelStorei(GL_UNPACK_SKIP_PIXELS_EXT, 0);
 		glPixelStorei(GL_UNPACK_SKIP_ROWS_EXT, 0);
 		wl_shm_buffer_begin_access(buffer->shm_buffer);
 		for (j = 0; j < gs->num_textures; j++) {
 			glBindTexture(GL_TEXTURE_2D, gs->textures[j]);
+			glPixelStorei(GL_UNPACK_ROW_LENGTH_EXT,
+				      gs->pitch / gs->hsub[j]);
 			glTexImage2D(GL_TEXTURE_2D, 0,
 				     gs->gl_format[j],
 				     gs->pitch / gs->hsub[j],
@@ -1473,10 +1473,14 @@ gl_renderer_flush_damage(struct weston_surface *surface)
 
 		r = weston_surface_to_buffer_rect(surface, rectangles[i]);
 
-		glPixelStorei(GL_UNPACK_SKIP_PIXELS_EXT, r.x1);
-		glPixelStorei(GL_UNPACK_SKIP_ROWS_EXT, r.y1);
 		for (j = 0; j < gs->num_textures; j++) {
 			glBindTexture(GL_TEXTURE_2D, gs->textures[j]);
+			glPixelStorei(GL_UNPACK_ROW_LENGTH_EXT,
+				      gs->pitch / gs->hsub[j]);
+			glPixelStorei(GL_UNPACK_SKIP_PIXELS_EXT,
+				      r.x1 / gs->hsub[j]);
+			glPixelStorei(GL_UNPACK_SKIP_ROWS_EXT,
+				      r.y1 / gs->hsub[j]);
 			glTexSubImage2D(GL_TEXTURE_2D, 0,
 					r.x1 / gs->hsub[j],
 					r.y1 / gs->vsub[j],