Optimize implementation of clear screen escape code

kitty/data-types.h

@@ -372,6 +372,8 @@ cursor_to_attrs(const Cursor *c, const uint16_t width) {
     return ans;
 }
 
+#define cursor_as_gpu_cell(cursor) {.attrs=cursor_to_attrs(cursor, 0), .fg=(cursor->fg & COL_MASK), .bg=(cursor->bg & COL_MASK), .decoration_fg=cursor->decoration_fg & COL_MASK}
+
 static inline void
 attrs_to_cursor(const CellAttrs attrs, Cursor *c) {
     c->decoration = attrs.decoration; c->bold = attrs.bold;  c->italic = attrs.italic;

kitty/line-buf.c

@@ -146,6 +146,22 @@ linebuf_init_line(LineBuf *self, index_type idx) {
     init_line(self, self->line, self->line_map[idx]);
 }
 
+void
+linebuf_clear_lines(LineBuf *self, const Cursor *cursor, index_type start, index_type end) {
+    GPUCell *first_gpu_line = gpu_lineptr(self, start);
+    GPUCell gc = cursor_as_gpu_cell(cursor);
+    for (index_type i = 0; i < self->xnum; i++) memcpy(first_gpu_line + i, &gc, sizeof(gc));
+    const size_t cpu_stride = sizeof(self->cpu_cell_buf[0]) * self->xnum;
+    memset(cpu_lineptr(self, start), 0, cpu_stride);
+    const size_t gpu_stride = sizeof(self->gpu_cell_buf[0]) * self->xnum;
+    linebuf_clear_attrs_and_dirty(self, start);
+    for (index_type i = start + 1; i < end; i++) {
+        memset(cpu_lineptr(self, i), 0, cpu_stride);
+        memcpy(gpu_lineptr(self, i), first_gpu_line, gpu_stride);
+        linebuf_clear_attrs_and_dirty(self, i);
+    }
+}
+
 static PyObject*
 line(LineBuf *self, PyObject *y) {
 #define line_doc      "Return the specified line as a Line object. Note the Line Object is a live view into the underlying buffer. And only a single line object can be used at a time."

kitty/line.c

@@ -539,8 +539,8 @@ clear_text(Line* self, PyObject *args) {
 }
 
 void
-line_apply_cursor(Line *self, Cursor *cursor, unsigned int at, unsigned int num, bool clear_char) {
-    GPUCell gc = {.attrs=cursor_to_attrs(cursor, 0), .fg=(cursor->fg & COL_MASK), .bg=(cursor->bg & COL_MASK), .decoration_fg=cursor->decoration_fg & COL_MASK};
+line_apply_cursor(Line *self, const Cursor *cursor, unsigned int at, unsigned int num, bool clear_char) {
+    GPUCell gc = cursor_as_gpu_cell(cursor);
     if (clear_char) {
         for (index_type i = at; i < self->xnum && i < at + num; i++) {
             memset(self->cpu_cells + i, 0, sizeof(self->cpu_cells[0]));

kitty/lineops.h

@@ -83,7 +83,7 @@ line_is_empty(const Line *line) {
 
 typedef Line*(get_line_func)(void *, int);
 void line_clear_text(Line *self, unsigned int at, unsigned int num, char_type ch);
-void line_apply_cursor(Line *self, Cursor *cursor, unsigned int at, unsigned int num, bool clear_char);
+void line_apply_cursor(Line *self, const Cursor *cursor, unsigned int at, unsigned int num, bool clear_char);
 char_type line_get_char(Line *self, index_type at);
 void line_set_char(Line *, unsigned int , uint32_t , unsigned int , Cursor *, hyperlink_id_type);
 void line_right_shift(Line *, unsigned int , unsigned int );
@@ -103,6 +103,7 @@ PyObject* line_as_unicode(Line *, bool);
 void linebuf_init_line(LineBuf *, index_type);
 void linebuf_init_cells(LineBuf *lb, index_type ynum, CPUCell **c, GPUCell **g);
 void linebuf_clear(LineBuf *, char_type ch);
+void linebuf_clear_lines(LineBuf *self, const Cursor *cursor, index_type start, index_type end);
 void linebuf_index(LineBuf* self, index_type top, index_type bottom);
 void linebuf_reverse_index(LineBuf *self, index_type top, index_type bottom);
 void linebuf_clear_line(LineBuf *self, index_type y, bool clear_attrs);

kitty/screen.c

@@ -1866,16 +1866,14 @@ screen_erase_in_display(Screen *self, unsigned int how, bool private) {
     }
     if (b > a) {
         if (how != 3) screen_dirty_line_graphics(self, a, b, self->linebuf == self->main_linebuf);
-        for (unsigned int i=a; i < b; i++) {
-            linebuf_init_line(self->linebuf, i);
-            if (private) {
+        if (private) {
+            for (unsigned int i=a; i < b; i++) {
+                linebuf_init_line(self->linebuf, i);
                 line_clear_text(self->linebuf->line, 0, self->columns, BLANK_CHAR);
                 linebuf_set_last_char_as_continuation(self->linebuf, i, false);
-            } else {
-                line_apply_cursor(self->linebuf->line, self->cursor, 0, self->columns, true);
+                linebuf_clear_attrs_and_dirty(self->linebuf, i);
             }
-            linebuf_clear_attrs_and_dirty(self->linebuf, i);
-        }
+        } else linebuf_clear_lines(self->linebuf, self->cursor, a, b);
         self->is_dirty = true;
         clear_selection(&self->selections);
     }