sixel: application configurable palette size (color count)

This implements the CSI escapes for retrieving and (re)setting the
palette size.

csi.c

@@ -15,6 +15,7 @@
 #include "grid.h"
 #include "vt.h"
 #include "selection.h"
+#include "sixel.h"
 
 #define min(x, y) ((x) < (y) ? (x) : (y))
 
@@ -1227,6 +1228,30 @@ csi_dispatch(struct terminal *term, uint8_t final)
             }
             break;
 
+        case 'S': {
+            unsigned target = vt_param_get(term, 0, 0);
+            unsigned operation = vt_param_get(term, 1, 0);
+
+            switch (target) {
+            case 1:
+                switch (operation) {
+                case 1: sixel_colors_report_current(term); break;
+                case 2: sixel_colors_reset(term); break;
+                case 3: sixel_colors_set(term, vt_param_get(term, 2, 0)); break;
+                case 4: sixel_colors_report_max(term);
+                }
+                break;
+
+            case 2:
+                break;
+
+            case 3:
+                break;
+
+            }
+            break;
+        }
+
         default:
             UNHANDLED();
             break;

sixel.c

@@ -11,7 +11,6 @@
 #define max(x, y) ((x) > (y) ? (x) : (y))
 #define min(x, y) ((x) < (y) ? (x) : (y))
 
-static const size_t COLOR_COUNT = 1024;
 
 static size_t count;
 
@@ -20,6 +19,7 @@ sixel_init(struct terminal *term)
 {
     assert(term->sixel.palette == NULL);
     assert(term->sixel.image.data == NULL);
+    assert(term->sixel.palette_size <= SIXEL_MAX_COLORS);
 
     term->sixel.state = SIXEL_DECSIXEL;
     term->sixel.pos = (struct coord){0, 0};
@@ -28,7 +28,7 @@ sixel_init(struct terminal *term)
     term->sixel.param = 0;
     term->sixel.param_idx = 0;
     memset(term->sixel.params, 0, sizeof(term->sixel.params));
-    term->sixel.palette = calloc(COLOR_COUNT, sizeof(term->sixel.palette[0]));
+    term->sixel.palette = calloc(term->sixel.palette_size, sizeof(term->sixel.palette[0]));
     term->sixel.image.data = malloc(1 * 6 * sizeof(term->sixel.image.data[0]));
     term->sixel.image.width = 1;
     term->sixel.image.height = 6;
@@ -309,10 +309,8 @@ decgci(struct terminal *term, uint8_t c)
 
         int nparams = term->sixel.param_idx;
 
-        if (nparams > 0) {
-            /* Add one, as we use idx==0 for background color (TODO) */
-            term->sixel.color_idx = min(1 + term->sixel.params[0], COLOR_COUNT - 1);
-        }
+        if (nparams > 0)
+            term->sixel.color_idx = min(term->sixel.params[0], term->sixel.palette_size - 1);
 
         if (nparams > 4) {
             unsigned format = term->sixel.params[1];
@@ -360,3 +358,34 @@ sixel_put(struct terminal *term, uint8_t c)
 
     count++;
 }
+
+void
+sixel_colors_report_current(struct terminal *term)
+{
+    char reply[24];
+    snprintf(reply, sizeof(reply), "\033[?1;0;%uS", term->sixel.palette_size);
+    term_to_slave(term, reply, strlen(reply));
+}
+
+void
+sixel_colors_reset(struct terminal *term)
+{
+    term->sixel.palette_size = SIXEL_MAX_COLORS;
+    LOG_DBG("sixel palette size reset to %u", SIXEL_MAX_COLORS);
+}
+
+void
+sixel_colors_set(struct terminal *term, unsigned count)
+{
+    unsigned new_palette_size = min(max(2, count), SIXEL_MAX_COLORS);
+    term->sixel.palette_size = new_palette_size;
+    LOG_DBG("sixel palette size set to %u", new_palette_size);
+}
+
+void
+sixel_colors_report_max(struct terminal *term)
+{
+    char reply[24];
+    snprintf(reply, sizeof(reply), "\033[?1;0;%uS", SIXEL_MAX_COLORS);
+    term_to_slave(term, reply, strlen(reply));
+}

sixel.h

@@ -2,8 +2,15 @@
 
 #include "terminal.h"
 
+#define SIXEL_MAX_COLORS 1024u
+
 void sixel_init(struct terminal *term);
 void sixel_put(struct terminal *term, uint8_t c);
 void sixel_unhook(struct terminal *term);
 
 void sixel_destroy(struct sixel *sixel);
+
+void sixel_colors_report_current(struct terminal *term);
+void sixel_colors_reset(struct terminal *term);
+void sixel_colors_set(struct terminal *term, unsigned count);
+void sixel_colors_report_max(struct terminal *term);

terminal.c

@@ -741,6 +741,9 @@ term_init(const struct config *conf, struct fdm *fdm, struct wayland *wayl,
             .lower_fd = delay_lower_fd,
             .upper_fd = delay_upper_fd,
         },
+        .sixel = {
+            .palette_size = SIXEL_MAX_COLORS,
+        },
         .sixel_images = tll_init(),
         .hold_at_exit = conf->hold_at_exit,
         .shutdown_cb = shutdown_cb,

terminal.h

@@ -376,6 +376,9 @@ struct terminal {
         unsigned params[5];  /* Collected parmaeters, for RASTER, COLOR_SPEC */
         unsigned param;      /* Currently collecting parameter, for RASTER, COLOR_SPEC and REPEAT */
         unsigned param_idx;  /* Parameters seen */
+
+        /* Application configurable */
+        unsigned palette_size;
     } sixel;
 
     tll(struct sixel) sixel_images;