[PATCH i-g-t] tests/kms_plane_cursor: Use two FBs for reference image

[Chaitanya Kumar Borah <chaitanya.kumar.borah@intel.com>]

Painting directly on the FB currently being scanned out ends up
modifying the frontbuffer. Since the FB isn’t marked dirty, those
updates never reach the actual buffer, leading to stale or incorrect
reference images during testing.

To avoid this, create two reference framebuffers and alternately flip
between them: one is displayed while the other is used for rendering
the reference image.

Signed-off-by: Chaitanya Kumar Borah <chaitanya.kumar.borah@intel.com>
---
 tests/kms_plane_cursor.c | 20 ++++++++++++++++++--
 1 file changed, 18 insertions(+), 2 deletions(-)

diff --git a/tests/kms_plane_cursor.c b/tests/kms_plane_cursor.c
index 9fa36bfd4..fa78b58ff 100644
--- a/tests/kms_plane_cursor.c
+++ b/tests/kms_plane_cursor.c
@@ -78,6 +78,7 @@ typedef struct data {
 	igt_pipe_t *pipe;
 	igt_pipe_crc_t *pipe_crc;
 	drmModeModeInfo *mode;
+	igt_fb_t ref_fb[2];
 	igt_fb_t pfb;
 	igt_fb_t ofb;
 	igt_fb_t cfb;
@@ -152,6 +153,7 @@ static void test_cursor_pos(data_t *data, int x, int y, unsigned int flags)
 {
 	igt_crc_t ref_crc, test_crc;
 	cairo_t *cr;
+	igt_fb_t *ref_fb;
 	igt_fb_t *pfb = &data->pfb;
 	igt_fb_t *ofb = &data->ofb;
 	igt_fb_t *cfb = &data->cfb;
@@ -159,8 +161,11 @@ static void test_cursor_pos(data_t *data, int x, int y, unsigned int flags)
 	int ch = cfb->height;
 	const rect_t *or = &data->or;
 
-	cr = igt_get_cairo_ctx(pfb->fd, pfb);
-	igt_paint_color(cr, 0, 0, pfb->width, pfb->height, 1.0, 1.0, 1.0);
+	ref_fb = (data->primary->drm_plane->fb_id ==
+		  data->ref_fb[0].fb_id) ? &data->ref_fb[1] : &data->ref_fb[0];
+
+	cr = igt_get_cairo_ctx(pfb->fd, ref_fb);
+	igt_paint_color(cr, 0, 0, ref_fb->width, ref_fb->height, 1.0, 1.0, 1.0);
 
 	if (flags & TEST_OVERLAY)
 		igt_paint_color(cr, or->x, or->y, or->w, or->h, 0.5, 0.5, 0.5);
@@ -168,6 +173,9 @@ static void test_cursor_pos(data_t *data, int x, int y, unsigned int flags)
 	igt_paint_color(cr, x, y, cw, ch, 1.0, 0.0, 1.0);
 	igt_put_cairo_ctx(cr);
 
+	igt_plane_set_fb(data->primary, ref_fb);
+	igt_display_commit_atomic(&data->display, 0, NULL);
+
 	if (flags & TEST_OVERLAY)
 		igt_plane_set_fb(data->overlay, NULL);
 	igt_plane_set_fb(data->cursor, NULL);
@@ -249,6 +257,8 @@ static void test_cleanup(data_t *data)
 	igt_remove_fb(data->drm_fd, &data->cfb);
 	igt_remove_fb(data->drm_fd, &data->ofb);
 	igt_remove_fb(data->drm_fd, &data->pfb);
+	igt_remove_fb(data->drm_fd, &data->ref_fb[0]);
+	igt_remove_fb(data->drm_fd, &data->ref_fb[1]);
 }
 
 static void test_cursor(data_t *data, int size, unsigned int flags)
@@ -263,6 +273,12 @@ static void test_cursor(data_t *data, int size, unsigned int flags)
 
 	test_cleanup(data);
 
+	igt_create_fb(data->drm_fd, sw, sh, DRM_FORMAT_XRGB8888,
+		      DRM_FORMAT_MOD_LINEAR, &data->ref_fb[0]);
+
+	igt_create_fb(data->drm_fd, sw, sh, DRM_FORMAT_XRGB8888,
+		      DRM_FORMAT_MOD_LINEAR, &data->ref_fb[1]);
+
 	igt_create_color_fb(data->drm_fd, sw, sh, DRM_FORMAT_XRGB8888,
 			    DRM_FORMAT_MOD_LINEAR, 1.0, 1.0, 1.0, &data->pfb);
 
-- 
2.25.1