rust: add visual module

rust/src/visual.rs

@@ -0,0 +1,44 @@
+// functions already exported by bindgen : 17
+// -----------------------------------------
+// ncvisual_at_yx
+// ncvisual_decode
+// ncvisual_decode_loop
+// ncvisual_destroy
+// ncvisual_from_bgra
+// ncvisual_from_file
+// ncvisual_from_plane
+// ncvisual_from_rgba
+// ncvisual_geom
+// ncvisual_polyfill_yx
+// ncvisual_render
+// ncvisual_resize
+// ncvisual_rotate
+// ncvisual_set_yx
+// ncvisual_simple_streamer
+// ncvisual_stream
+// ncvisual_subtitle
+//
+// static inline functions total: 1
+// ------------------------------------------ (done / remaining)
+// (+) done: 0 / 1
+// (#) test: 0 / 1
+// ------------------------------------------
+// ncvisual_default_blitter
+
+use crate as nc;
+use nc::types::{BLIT_1x1, BLIT_2x1, BLIT_2x2, Blitter, Scale, SCALE_STRETCH};
+
+/// Returns the best default blitter available
+///
+/// NCBLIT_3x2 is better image quality, especially for large images, but
+/// it's not the general default because it doesn't preserve aspect ratio.
+/// NCSCALE_STRETCH throws away aspect ratio, and can safely use NCBLIT_3x2.
+pub fn ncvisual_default_blitter(utf8: bool, scale: Scale) -> Blitter {
+    if utf8 {
+        if scale == SCALE_STRETCH {
+            return BLIT_2x2;
+        }
+        return BLIT_2x1;
+    }
+    BLIT_1x1;
+}