Use NCBLIT_2x2 by default with NCSCALE_STRETCH

We're not using NCBLIT_2x2 by default because it warps the
aspect ratio. If we're using NCSCALE_STRETCH, though, we've
(1) already indicated that aspect ratio isn't terribly
important to us and (2) are trying to maximize the space.
Since NCBLIT_2x2 is best for large images anyway, make it
the default when NCSCALE_STRECTH is being used.

Remove all explicit uses of NCBLIT_2x2 when NCSCALE_STRETCH
is being used in notcurses-demo.

NEWS.md

@@ -1,6 +1,11 @@
 This document attempts to list user-visible changes and any major internal
 rearrangements of Notcurses.
 
+* 1.5.3 (not yet released)
+  * The default blitter when `NCSCALE_STRETCH` is used is now `NCBLIT_2x2`,
+    replacing `NCBLIT_2x1`. It is not the default for `NCSCALE_NONE` and
+    `NCSCALE_SCALE` because it does not preserve aspect ratio.
+
 * 1.5.2 (2020-06-19)
   * The `ncneofetch` program has been added, of no great consequence.
   * A `NULL` value can now be passed as `sbytes` to `ncplane_puttext()`.

src/demo/luigi.c

@@ -157,7 +157,6 @@ int luigi_demo(struct notcurses* nc){
   struct ncvisual_options vopts = {
     .n = notcurses_stddim_yx(nc, &rows, &cols),
     .scaling = NCSCALE_STRETCH,
-    .blitter = NCBLIT_2x2,
   };
   if(ncvisual_render(nc, nv, &vopts) == NULL){
     return -1;

src/demo/normal.c

@@ -86,7 +86,6 @@ rotate_visual(struct notcurses* nc, struct ncplane* n, int dy, int dx){
       if(nncv){
         struct ncvisual_options nvopts = {
           .n = notcurses_stdplane(nc),
-          .blitter = NCBLIT_2x2,
           .y = 1,
           .scaling = NCSCALE_STRETCH,
         };

src/demo/outro.c

@@ -59,7 +59,6 @@ videothread(void* vnc){
     .scaling = NCSCALE_STRETCH,
     .n = ncp,
     .y = 1,
-    .blitter = NCBLIT_2x2,
   };
   int three = 3;
   if(ncvisual_render(nc, ncv, &ovopts) == NULL){

src/demo/view.c

@@ -15,7 +15,6 @@ view_video_demo(struct notcurses* nc){
   struct ncvisual_options vopts = {
     .scaling = NCSCALE_STRETCH,
     .n = ncp,
-    .blitter = NCBLIT_2x2,
     .y = 1,
   };
   int ret = ncvisual_stream(nc, ncv, &err, 0.5 * delaymultiplier,
@@ -81,7 +80,6 @@ view_images(struct notcurses* nc, struct ncplane* nstd, int dimy, int dimx){
   struct ncvisual_options vopts = {
     .n = dsplane,
     .scaling = NCSCALE_STRETCH,
-    .blitter = NCBLIT_2x2,
     .y = 1,
   };
   if(ncvisual_render(nc, ncv2, &vopts) == NULL){
@@ -107,7 +105,6 @@ view_images(struct notcurses* nc, struct ncplane* nstd, int dimy, int dimx){
   }
   free(pic);
   vopts.n = notcurses_stdplane(nc);
-  vopts.blitter = NCBLIT_2x2;
   if(ncvisual_render(nc, ncv, &vopts) == NULL){
     ncvisual_destroy(ncv);
     ncplane_destroy(dsplane);

src/demo/xray.c

@@ -94,6 +94,7 @@ int xray_demo(struct notcurses* nc){
   struct ncvisual_options vopts = {
     .n = n,
     .scaling = NCSCALE_STRETCH,
+    .blitter = NCBLIT_2x1,
   };
   int ret = ncvisual_stream(nc, ncv, &err, 0.5 * delaymultiplier, perframecb, &vopts, newpanel);
   ncvisual_destroy(ncv);

src/lib/visual.cpp

@@ -29,8 +29,14 @@ encoding_x_scale(const struct blitset* bset) -> int {
 }
 
 static inline auto
-ncvisual_default_blitter(const notcurses* nc) -> ncblitter_e {
+ncvisual_default_blitter(const notcurses* nc, ncscale_e scale) -> ncblitter_e {
   if(notcurses_canutf8(nc)){
+    // NCBLIT_2x2 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_2x2.
+    if(scale == NCSCALE_STRETCH){
+      return NCBLIT_2x2;
+    }
     return NCBLIT_2x1;
   }
   return NCBLIT_1x1;
@@ -48,9 +54,10 @@ void scale_visual(const ncvisual* ncv, int* disprows, int* dispcols) {
 auto ncvisual_geom(const notcurses* nc, const ncvisual* n,
                    const struct ncvisual_options* vopts,
                    int* y, int* x, int* toy, int* tox) -> int {
+  const ncscale_e scale = vopts ? vopts->scaling : NCSCALE_NONE;
   ncblitter_e blitter;
   if(!vopts || vopts->blitter == NCBLIT_DEFAULT){
-    blitter = ncvisual_default_blitter(nc);
+    blitter = ncvisual_default_blitter(nc, scale);
   }else{
     blitter = vopts->blitter;
   }
@@ -67,19 +74,16 @@ auto ncvisual_geom(const notcurses* nc, const ncvisual* n,
     x = &fauxx;
   }
   if(n){
-    if(!vopts || vopts->scaling == NCSCALE_NONE){
+    if(scale == NCSCALE_NONE){
       *y = n->rows;
-    }else{
-      int rows = vopts->n ? ncplane_dim_y(vopts->n) : ncplane_dim_y(nc->stdscr);
-      *y = rows * encoding_y_scale(bset);
-    }
-    if(!vopts || vopts->scaling == NCSCALE_NONE){
       *x = n->cols;
     }else{
+      int rows = vopts->n ? ncplane_dim_y(vopts->n) : ncplane_dim_y(nc->stdscr);
       int cols = vopts->n ? ncplane_dim_x(vopts->n) : ncplane_dim_x(nc->stdscr);
+      *y = rows * encoding_y_scale(bset);
       *x = cols * encoding_x_scale(bset);
     }
-    if(vopts && vopts->scaling == NCSCALE_SCALE){
+    if(scale == NCSCALE_SCALE){
       scale_visual(n, y, x);
     }
   }
@@ -98,10 +102,11 @@ static const struct blitset*
 rgba_blitter(const notcurses* nc, const struct ncvisual_options* opts){
   const struct blitset* bset;
   const bool maydegrade = !(opts && (opts->flags & NCVISUAL_OPTION_NODEGRADE));
+  const ncscale_e scale = opts ? opts->scaling : NCSCALE_NONE;
   if(opts && opts->blitter != NCBLIT_DEFAULT){
     bset = lookup_blitset(nc, opts->blitter, maydegrade);
   }else{
-    bset = lookup_blitset(nc, ncvisual_default_blitter(nc), maydegrade);
+    bset = lookup_blitset(nc, ncvisual_default_blitter(nc, scale), maydegrade);
   }
   if(bset && !bset->blit){ // FIXME remove this once all blitters are enabled
     bset = nullptr;

src/poc/visual.cpp

@@ -20,7 +20,7 @@ int main(int argc, char** argv){
     file = argv[1];
   }
   notcurses_options opts{};
-  opts.loglevel = NCLOGLEVEL_TRACE;
+  //opts.loglevel = NCLOGLEVEL_TRACE;
   opts.flags = NCOPTION_INHIBIT_SETLOCALE | NCOPTION_NO_ALTERNATE_SCREEN;
   struct notcurses* nc;
   if((nc = notcurses_init(&opts, nullptr)) == nullptr){