grid: attributes now track whether we've set a foreground/background color

This means we don't have to explicitly set the foreground/background
to the grid's default colors whenever we reset/clear a cell, and we
can instead simply memset() the entire cell to 0.

This also means the renderer has to get the default color when
rendering a cell without a foreground/background color set.

csi.c

@@ -75,14 +75,8 @@ param_get(const struct terminal *term, size_t idx, int default_value)
 static void
 sgr_reset(struct terminal *term)
 {
-    term->vt.attrs.bold = false;
+    memset(&term->vt.attrs, 0, sizeof(term->vt.attrs));
     term->vt.dim = false;
-    term->vt.attrs.italic = false;
-    term->vt.attrs.underline = false;
-    term->vt.attrs.strikethrough = false;
-    term->vt.attrs.blink = false;
-    term->vt.attrs.conceal = false;
-    term->vt.attrs.reverse = false;
     term->vt.attrs.foreground = term->grid.foreground;
     term->vt.attrs.background = term->grid.background;
 }
@@ -130,6 +124,7 @@ csi_sgr(struct terminal *term)
         case 35:
         case 36:
         case 37:
+            term->vt.attrs.have_foreground = true;
             term->vt.attrs.foreground = colors_regular[param - 30];
             break;
 
@@ -139,6 +134,7 @@ csi_sgr(struct terminal *term)
             {
                 size_t idx = term->vt.params.v[i + 2].value;
                 term->vt.attrs.foreground = colors256[idx];
+                term->vt.attrs.have_foreground = true;
                 i += 2;
             } else if (term->vt.params.idx - i - 1 == 4 &&
                        term->vt.params.v[i + 1].value == 2)
@@ -147,6 +143,7 @@ csi_sgr(struct terminal *term)
                 uint32_t g = term->vt.params.v[i + 3].value;
                 uint32_t b = term->vt.params.v[i + 4].value;
                 term->vt.attrs.foreground = r << 24 | g << 16 | b << 8 | 0xff;
+                term->vt.attrs.have_foreground = true;
                 i += 4;
             } else {
                 LOG_ERR("invalid CSI SGR sequence");
@@ -154,7 +151,10 @@ csi_sgr(struct terminal *term)
             }
             break;
         }
-        case 39: term->vt.attrs.foreground = term->grid.foreground; break;
+        case 39:
+            term->vt.attrs.foreground = term->grid.foreground;
+            term->vt.attrs.have_foreground = false;
+            break;
 
         /* Regular background colors */
         case 40:
@@ -166,6 +166,7 @@ csi_sgr(struct terminal *term)
         case 46:
         case 47:
             term->vt.attrs.background = colors_regular[param - 40];
+            term->vt.attrs.have_background = true;
             break;
 
         case 48: {
@@ -174,6 +175,7 @@ csi_sgr(struct terminal *term)
             {
                 size_t idx = term->vt.params.v[i + 2].value;
                 term->vt.attrs.background = colors256[idx];
+                term->vt.attrs.have_background = true;
                 i += 2;
             } else if (term->vt.params.idx - i - 1 == 4 &&
                        term->vt.params.v[i + 1].value == 2)
@@ -182,6 +184,7 @@ csi_sgr(struct terminal *term)
                 uint32_t g = term->vt.params.v[i + 3].value;
                 uint32_t b = term->vt.params.v[i + 4].value;
                 term->vt.attrs.background = r << 24 | g << 16 | b << 8 | 0xff;
+                term->vt.attrs.have_background = true;
                 i += 4;
             } else {
                 LOG_ERR("invalid CSI SGR sequence");
@@ -189,7 +192,10 @@ csi_sgr(struct terminal *term)
             }
             break;
         }
-        case 49: term->vt.attrs.background = term->grid.background; break;
+        case 49:
+            term->vt.attrs.background = term->grid.background;
+            term->vt.attrs.have_background = false;
+            break;
 
         /* Bright foreground colors */
         case 90:
@@ -201,6 +207,7 @@ csi_sgr(struct terminal *term)
         case 96:
         case 97:
             term->vt.attrs.foreground = colors_bright[param - 90];
+            term->vt.attrs.have_foreground = true;
             break;
 
         /* Regular background colors */
@@ -213,6 +220,7 @@ csi_sgr(struct terminal *term)
         case 106:
         case 107:
             term->vt.attrs.background = colors_bright[param - 100];
+            term->vt.attrs.have_background = true;
             break;
 
         default:

grid.c

@@ -187,14 +187,6 @@ grid_erase(struct grid *grid, int start, int end)
 {
     assert(end >= start);
     memset(&grid->cells[start], 0, (end - start) * sizeof(grid->cells[0]));
-
-    for (int i = start; i < end; i++) {
-        struct cell *cell = &grid->cells[i];
-
-        cell->attrs.foreground = grid->foreground;
-        cell->attrs.background = grid->background;
-    }
-
     grid_damage_erase(grid, start, end - start);
 }
 

main.c

@@ -102,8 +102,10 @@ grid_render_update(struct context *c, struct buffer *buf, const struct damage *d
         int width = c->term.grid.cell_width;
         int height = c->term.grid.cell_height;
 
-        uint32_t foreground = cell->attrs.foreground;
+        uint32_t foreground = cell->attrs.have_foreground
-        uint32_t background = cell->attrs.background;
+            ? cell->attrs.foreground : c->term.grid.foreground;
+        uint32_t background = cell->attrs.have_background
+            ? cell->attrs.background : c->term.grid.background;
 
         if (has_cursor) {
             uint32_t swap = foreground;

terminal.h

@@ -19,8 +19,10 @@ struct attributes {
     bool blink;
     bool conceal;
     bool reverse;
-    uint32_t foreground;
+    bool have_foreground;
-    uint32_t background;
+    bool have_background;
+    uint32_t foreground;  /* Only valid when have_foreground == true */
+    uint32_t background;  /* Only valid when have_background == true */
 };
 
 struct cell {