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tinywl: Fix wrong anchor point while resizing a window
Previously, when dragging the left border of a window with the mouse in tinywl,
there was a bug where it snap the top level surface's geometry X coordinate
directly to the position of the mouse, as if you started the resize right on the
border. This also affected the other (right, top and bottom) borders.

I think that the previous resize code was hard to understand. Honestly I
have not spent a lot of time trying to understand why it didn't work and
I wrote another resize algorithm instead: now, instead of working directly
with widths and heights which are complicated, we work with the borders (left,
right, top, bottom). This is easier to understand IMO.

Note: I originally fixed this [in the waybox compositor](wizbright/waybox#23) but
then I realized that the code was taken from tinywl and that it had the same
issues so I copied my fix for tinywl.
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1kjo authored and ddevault committed Apr 28, 2020
1 parent 321537e commit 21397e2
Showing 1 changed file with 45 additions and 27 deletions.
72 changes: 45 additions & 27 deletions tinywl/tinywl.c
Expand Up @@ -55,8 +55,7 @@ struct tinywl_server {
enum tinywl_cursor_mode cursor_mode;
struct tinywl_view *grabbed_view;
double grab_x, grab_y;
struct wlr_box grab_geo_box;
int grab_width, grab_height;
struct wlr_box grab_geobox;
uint32_t resize_edges;

struct wlr_output_layout *output_layout;
Expand Down Expand Up @@ -370,33 +369,44 @@ static void process_cursor_resize(struct tinywl_server *server, uint32_t time) {
* commit any movement that was prepared.
*/
struct tinywl_view *view = server->grabbed_view;
double dx = server->cursor->x - server->grab_x;
double dy = server->cursor->y - server->grab_y;
double x = view->x;
double y = view->y;
int width = server->grab_width;
int height = server->grab_height;
double border_x = server->cursor->x - server->grab_x;
double border_y = server->cursor->y - server->grab_y;
int new_left = server->grab_geobox.x;
int new_right = server->grab_geobox.x + server->grab_geobox.width;
int new_top = server->grab_geobox.y;
int new_bottom = server->grab_geobox.y + server->grab_geobox.height;

if (server->resize_edges & WLR_EDGE_TOP) {
y = server->grab_y + dy - server->grab_geo_box.y;
height -= dy + server->grab_geo_box.y;
if (height < 1) {
y += height;
new_top = border_y;
if (new_top >= new_bottom) {
new_top = new_bottom - 1;
}
} else if (server->resize_edges & WLR_EDGE_BOTTOM) {
height += dy + server->grab_geo_box.y;
new_bottom = border_y;
if (new_bottom <= new_top) {
new_bottom = new_top + 1;
}
}
if (server->resize_edges & WLR_EDGE_LEFT) {
x = server->grab_x + dx - server->grab_geo_box.x;
width -= dx + server->grab_geo_box.x;
if (width < 1) {
x += width;
new_left = border_x;
if (new_left >= new_right) {
new_left = new_right - 1;
}
} else if (server->resize_edges & WLR_EDGE_RIGHT) {
width += dx + server->grab_geo_box.x;
new_right = border_x;
if (new_right <= new_left) {
new_right = new_left + 1;
}
}
view->x = x;
view->y = y;
wlr_xdg_toplevel_set_size(view->xdg_surface, width, height);

struct wlr_box geo_box;
wlr_xdg_surface_get_geometry(view->xdg_surface, &geo_box);
view->x = new_left - geo_box.x;
view->y = new_top - geo_box.y;

int new_width = new_right - new_left;
int new_height = new_bottom - new_top;
wlr_xdg_toplevel_set_size(view->xdg_surface, new_width, new_height);
}

static void process_cursor_motion(struct tinywl_server *server, uint32_t time) {
Expand Down Expand Up @@ -725,17 +735,25 @@ static void begin_interactive(struct tinywl_view *view,
}
server->grabbed_view = view;
server->cursor_mode = mode;
wlr_xdg_surface_get_geometry(view->xdg_surface, &server->grab_geo_box);

if (mode == TINYWL_CURSOR_MOVE) {
server->grab_x = server->cursor->x - view->x;
server->grab_y = server->cursor->y - view->y;
} else {
server->grab_x = server->cursor->x + server->grab_geo_box.x;
server->grab_y = server->cursor->y + server->grab_geo_box.y;
struct wlr_box geo_box;
wlr_xdg_surface_get_geometry(view->xdg_surface, &geo_box);

double border_x = (view->x + geo_box.x) + ((edges & WLR_EDGE_RIGHT) ? geo_box.width : 0);
double border_y = (view->y + geo_box.y) + ((edges & WLR_EDGE_BOTTOM) ? geo_box.height : 0);
server->grab_x = server->cursor->x - border_x;
server->grab_y = server->cursor->y - border_y;

server->grab_geobox = geo_box;
server->grab_geobox.x += view->x;
server->grab_geobox.y += view->y;

server->resize_edges = edges;
}
server->grab_width = server->grab_geo_box.width;
server->grab_height = server->grab_geo_box.height;
server->resize_edges = edges;
}

static void xdg_toplevel_request_move(
Expand Down

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