transfer: allow optional extrapolation

2 files changed, 8 insertions, 2 deletions

diff --git a/transfer.c b/transfer.c
index 6db1ad2..9c5e125 100644
--- a/transfer.c
+++ b/transfer.c
@@ -425,8 +425,8 @@ int mg2di_gt_init(GridTransferContext *ctx)
             ctx->src.size[i] < 2 || ctx->dst.size[i] < 1)
             return -EINVAL;
 
-        src_start = ctx->src.start[i] * ctx->src.step[i];
-        src_end   = (ctx->src.start[i] + ctx->src.size[i] - 1) * ctx->src.step[i];
+        src_start = ctx->src.start[i] * ctx->src.step[i] - ctx->extrapolate_distance;
+        src_end   = (ctx->src.start[i] + ctx->src.size[i] - 1 + ctx->extrapolate_distance) * ctx->src.step[i];
         dst_start = ctx->dst.start[i] * ctx->dst.step[i];
         dst_end   = (ctx->dst.start[i] + ctx->dst.size[i] - 1) * ctx->dst.step[i];
 
diff --git a/transfer.h b/transfer.h
index 0a10f3a..2ed4aea 100644
--- a/transfer.h
+++ b/transfer.h
@@ -85,6 +85,12 @@ typedef struct GridTransferContext {
      * Destination grid geometry, must be filled by the caller.
      */
     RegularGrid2D dst;
+
+    /**
+     * Allow extrapolating this many points beyond the source rectangle.
+     * Defaults to 0: forbid extrapolation.
+     */
+    int extrapolate_distance;
 } GridTransferContext;
 
 /**