From 9b0c2e8bad87100f042144bc251b60b64f646c99 Mon Sep 17 00:00:00 2001
From: Benjamin Berg <bberg@redhat.com>
Date: Fri, 6 Dec 2019 18:55:52 +0100
Subject: [PATCH 158/181] fpi-assembling: Fix offsets to be relative to the
 previous frame

The offset stored for a frame was not always relative to the previous
frame. This was the case for reverse movement, but for forwrad movement
the offset was the one to the next frame.

Make the offset handling consistent and alwasy store the offset to the
previous frame. Also update the frame assembling code to add the offset
before blitting the frame (i.e. making it relative to the previous frame
there too).

Note that fpi_assemble_lines already made the assumption that this was
the case as it forced the offset for the first frame to be zero. As
such, the code was inconsistent.

This could affect the AES drivers slightly as they use hardware reported
values which might not adhere to these assumptions.
---
 libfprint/fpi-assembling.c | 34 +++++++++++++++++-----------------
 1 file changed, 17 insertions(+), 17 deletions(-)

diff --git a/libfprint/fpi-assembling.c b/libfprint/fpi-assembling.c
index a809a2d..6d34679 100644
--- a/libfprint/fpi-assembling.c
+++ b/libfprint/fpi-assembling.c
@@ -99,6 +99,8 @@ static void
 find_overlap (struct fpi_frame_asmbl_ctx *ctx,
               struct fpi_frame           *first_frame,
               struct fpi_frame           *second_frame,
+              int                        *dx_out,
+              int                        *dy_out,
               unsigned int               *min_error)
 {
   int dx, dy;
@@ -120,8 +122,8 @@ find_overlap (struct fpi_frame_asmbl_ctx *ctx,
           if (err < *min_error)
             {
               *min_error = err;
-              second_frame->delta_x = -dx;
-              second_frame->delta_y = dy;
+              *dx_out = -dx;
+              *dy_out = dy;
             }
         }
     }
@@ -133,7 +135,7 @@ do_movement_estimation (struct fpi_frame_asmbl_ctx *ctx,
 {
   GSList *l;
   GTimer *timer;
-  guint num_frames = 0;
+  guint num_frames = 1;
   struct fpi_frame *prev_stripe;
   unsigned int min_error;
   /* Max error is width * height * 255, for AES2501 which has the largest
@@ -143,20 +145,27 @@ do_movement_estimation (struct fpi_frame_asmbl_ctx *ctx,
   unsigned long long total_error = 0;
 
   timer = g_timer_new ();
+
+  /* Skip the first frame */
   prev_stripe = stripes->data;
-  for (l = stripes; l != NULL; l = l->next, num_frames++)
+
+  for (l = stripes->next; l != NULL; l = l->next, num_frames++)
     {
       struct fpi_frame *cur_stripe = l->data;
 
       if (reverse)
         {
-          find_overlap (ctx, prev_stripe, cur_stripe, &min_error);
+          find_overlap (ctx, prev_stripe, cur_stripe,
+                        &cur_stripe->delta_x, &cur_stripe->delta_y,
+                        &min_error);
           cur_stripe->delta_y = -cur_stripe->delta_y;
           cur_stripe->delta_x = -cur_stripe->delta_x;
         }
       else
         {
-          find_overlap (ctx, cur_stripe, prev_stripe, &min_error);
+          find_overlap (ctx, cur_stripe, prev_stripe,
+                        &cur_stripe->delta_x, &cur_stripe->delta_y,
+                        &min_error);
         }
       total_error += min_error;
 
@@ -328,19 +337,10 @@ fpi_assemble_frames (struct fpi_frame_asmbl_ctx *ctx,
     {
       fpi_frame = l->data;
 
-      if(reverse)
-        {
-          y += fpi_frame->delta_y;
-          x += fpi_frame->delta_x;
-        }
+      y += fpi_frame->delta_y;
+      x += fpi_frame->delta_x;
 
       aes_blit_stripe (ctx, img, fpi_frame, x, y);
-
-      if(!reverse)
-        {
-          y += fpi_frame->delta_y;
-          x += fpi_frame->delta_x;
-        }
     }
 
   return img;
-- 
2.24.1