image: add simple offset test

Makefile.am

@@ -327,6 +327,7 @@ TEST_BIN = 			\
     test/hmac			\
     test/hotp			\
     test/hton			\
+    test/image			\
     test/introspection		\
     test/ip 			\
     test/json_types		\

test/image.cpp

@@ -0,0 +1,33 @@
+#include "image.hpp"
+#include "tap.hpp"
+
+#include <cstdint>
+
+int
+main (void)
+{
+    util::TAP::logger tap;
+
+    constexpr size_t W = 64;
+    constexpr size_t H = 128;
+    util::image::buffer<uint16_t> img (W, H);
+
+    if (!img.is_packed ())
+        tap.skip ("linear position probe requires packed image allocation");
+    else {
+        // write out sequential values at each pixel, row-major
+        size_t i = 0;
+        for (size_t y = 0; y < H; ++y)
+            for (size_t x = 0; x < W; ++x)
+                img[{x,y}] = i++;
+
+        // check pixel values are sequential in row-major order
+        bool success = true;
+        for (size_t j = 0; j < i; ++j)
+            success = success && img[j] == j;
+
+        tap.expect (success, "linear position probe");
+    }
+
+    return tap.status ();
+}