Mesa (main): drisw: do an MSAA resolve when copying the backbuffer

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Module: Mesa
Branch: main
Commit: f0eb163ae0535ead5e89fd9d66dfc4b04488eb62
URL:    http://cgit.freedesktop.org/mesa/mesa/commit/?id=f0eb163ae0535ead5e89fd9d66dfc4b04488eb62

Author: Italo Nicola <italonicola at collabora.com>
Date:   Fri Jul  9 07:34:02 2021 -0300

drisw: do an MSAA resolve when copying the backbuffer

When calling glXCopySubBuffer, we must resolve the backbuffer before
copying it the frontbuffer.

Fixes piglit's glx/glx-copy-sub-buffer on virgl.

Signed-off-by: Italo Nicola <italonicola at collabora.com>
Reviewed-by: Gert Wollny <gert.wollny at collabora.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/11714>

---

 src/gallium/frontends/dri/drisw.c | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/src/gallium/frontends/dri/drisw.c b/src/gallium/frontends/dri/drisw.c
index adb486ceb0b..64c77889de4 100644
--- a/src/gallium/frontends/dri/drisw.c
+++ b/src/gallium/frontends/dri/drisw.c
@@ -285,6 +285,13 @@ drisw_copy_sub_buffer(__DRIdrawable *dPriv, int x, int y,
 
       ctx->st->flush(ctx->st, ST_FLUSH_FRONT, NULL, NULL, NULL);
 
+      if (drawable->stvis.samples > 1) {
+         /* Resolve the back buffer. */
+         dri_pipe_blit(ctx->st->pipe,
+                       drawable->textures[ST_ATTACHMENT_BACK_LEFT],
+                       drawable->msaa_textures[ST_ATTACHMENT_BACK_LEFT]);
+      }
+
       u_box_2d(x, dPriv->h - y - h, w, h, &box);
       drisw_present_texture(ctx->st->pipe, dPriv, ptex, &box);
    }