resizor: add centered resize

Use LMB for bottom-right anchored resize, RMB for centered resize.

Implements emersion#19

resizor.c

@@ -2,14 +2,19 @@
 #include <stdio.h>
 #include <stdlib.h>
 #include <string.h>
+#include <wayland-client-protocol.h>
 #include "client.h"
 
 static struct wleird_toplevel toplevel = {0};
 
 struct {
 	int x, y;
 	int last_x, last_y;
-	bool resizing;
+	enum {
+		RESIZING_NONE = 0,
+		RESIZING_ANCHORED_TO_BOTTOM_RIGHT,
+		RESIZING_ANCHORED_TO_CENTER,
+	} resizing;
 } pointer_state;
 
 static void pointer_handle_enter(void *data, struct wl_pointer *wl_pointer,
@@ -30,13 +35,19 @@ static void pointer_handle_motion(void *data, struct wl_pointer *wl_pointer,
 	pointer_state.y = wl_fixed_to_int(surface_y);
 
 	if (pointer_state.resizing) {
-		int dx = pointer_state.x - pointer_state.last_x;
-		int dy = pointer_state.y - pointer_state.last_y;
+		int dwidth = pointer_state.x - pointer_state.last_x;
+		int dheight = pointer_state.y - pointer_state.last_y;
+		int dx = dwidth, dy = dheight;
+
+		if (pointer_state.resizing == RESIZING_ANCHORED_TO_CENTER) {
+			dwidth *= 2;
+			dheight *= 2;
+		}
 
 		toplevel.surface.attach_x = dx;
 		toplevel.surface.attach_y = dy;
-		toplevel.surface.width -= dx;
-		toplevel.surface.height -= dy;
+		toplevel.surface.width -= dwidth;
+		toplevel.surface.height -= dheight;
 		surface_render(&toplevel.surface);
 	}
 
@@ -47,7 +58,15 @@ static void pointer_handle_motion(void *data, struct wl_pointer *wl_pointer,
 static void pointer_handle_button(void *data, struct wl_pointer *wl_pointer,
 		uint32_t serial, uint32_t time, uint32_t button,
 		uint32_t button_state) {
-	pointer_state.resizing = (button_state == WL_POINTER_BUTTON_STATE_PRESSED);
+	if (button_state == WL_POINTER_BUTTON_STATE_PRESSED) {
+		if (button == BTN_LEFT) {
+			pointer_state.resizing = RESIZING_ANCHORED_TO_BOTTOM_RIGHT;
+		} else if (button == BTN_RIGHT) {
+			pointer_state.resizing = RESIZING_ANCHORED_TO_CENTER;
+		}
+	} else {
+		pointer_state.resizing = RESIZING_NONE;
+	}
 
 	pointer_state.last_x = pointer_state.x;
 	pointer_state.last_y = pointer_state.y;