selection: selections can be made, and are rendered

* Start selection on mouse button down
* Update selection on motion
* Button release cancels selection if there were no motion after start
* Renderer detects cells inside the selection and inverts their colors

input.c

@@ -312,6 +312,14 @@ wl_pointer_motion(void *data, struct wl_pointer *wl_pointer,
     term->mouse.col = col;
     term->mouse.row = row;
 
+    if (term->mouse.button != 0) {
+        /* Update selection */
+        term->selection.end = (struct coord){col, term->grid->view + row};
+        term_damage_view(term);
+        if (term->frame_callback == NULL)
+            grid_render(term);
+    }
+
     term_mouse_motion(
         term, term->mouse.button, term->mouse.row, term->mouse.col,
         term->kbd.shift, term->kbd.alt, term->kbd.ctrl);
@@ -327,12 +335,25 @@ wl_pointer_button(void *data, struct wl_pointer *wl_pointer,
 
     switch (state) {
     case WL_POINTER_BUTTON_STATE_PRESSED:
+        /* Start selection */
+        term->selection.start = (struct coord){
+            term->mouse.col, term->grid->view + term->mouse.row};
+        term->selection.end = (struct coord){-1, -1};
+
         term->mouse.button = button; /* For motion events */
         term_mouse_down(term, button, term->mouse.row, term->mouse.col,
                         term->kbd.shift, term->kbd.alt, term->kbd.ctrl);
         break;
 
     case WL_POINTER_BUTTON_STATE_RELEASED:
+        if (term->selection.end.col == -1) {
+            /* No selection made - cancel  */
+            term->selection.start = (struct coord){-1, -1};
+            term_damage_view(term);
+            if (term->frame_callback == NULL)
+                grid_render(term);
+        }
+
         term->mouse.button = 0; /* For motion events */
         term_mouse_up(term, button, term->mouse.row, term->mouse.col,
                       term->kbd.shift, term->kbd.alt, term->kbd.ctrl);

main.c

@@ -313,6 +313,10 @@ main(int argc, char *const *argv)
         },
         .foreground = default_foreground,
         .background = default_background,
+        .selection = {
+            .start = {-1, -1},
+            .end = {-1, -1},
+        },
         .normal = {.damage = tll_init(), .scroll_damage = tll_init()},
         .alt = {.damage = tll_init(), .scroll_damage = tll_init()},
         .grid = &term.normal,

render.c

@@ -42,6 +42,32 @@ render_cell(struct terminal *term, struct buffer *buf, const struct cell *cell,
     double x = col * width;
     double y = row * height;
 
+    bool is_selected = false;
+    if (term->selection.start.col != -1 && term->selection.end.col != -1) {
+        const struct coord *start = &term->selection.start;
+        const struct coord *end = &term->selection.end;
+
+        if (end->row < start->row || (end->row == start->row && end->col < start->col)) {
+            const struct coord *tmp = start;
+            start = end;
+            end = tmp;
+        }
+
+        assert(start->row <= end->row);
+
+        if (start->row == end->row) {
+            is_selected
+                = term->grid->view + row == start->row && col >= start->col && col <= end->col;
+        } else {
+            if (term->grid->view + row == start->row)
+                is_selected = col >= start->col;
+            else if (term->grid->view + row == end->row)
+                is_selected = col <= end->col;
+            else
+                is_selected = term->grid->view + row >= start->row && term->grid->view + row <= end->row;
+        }
+    }
+
     const struct rgb *foreground = cell->attrs.have_foreground
         ? &cell->attrs.foreground
         : !term->reverse ? &term->foreground : &term->background;
@@ -50,7 +76,7 @@ render_cell(struct terminal *term, struct buffer *buf, const struct cell *cell,
         : !term->reverse ? &term->background : &term->foreground;
 
     /* If *one* is set, we reverse */
-    if (has_cursor ^ cell->attrs.reverse) {
+    if (has_cursor ^ cell->attrs.reverse ^ is_selected) {
         const struct rgb *swap = foreground;
         foreground = background;
         background = swap;

terminal.h

@@ -228,6 +228,11 @@ struct terminal {
     struct coord saved_cursor;
     struct coord alt_saved_cursor;
 
+    struct {
+        struct coord start;
+        struct coord end;
+    } selection;
+
     struct grid normal;
     struct grid alt;
     struct grid *grid;