Implemented setResizeCallback and setViewport

src/main.zig

@@ -106,6 +106,18 @@ fn handleActive(win: mfb.Window(State), isActive: bool) callconv(.C) void {
     }
 }
 
+fn handleResize(win: mfb.Window(State), width: i32, height: i32) callconv(.C) void {
+    const did_set = win.setViewport(
+        @intCast(u32, width) / 4,
+        @intCast(u32, height) / 4,
+        @intCast(u32, width) / 2,
+        @intCast(u32, height) / 2,
+        );
+    if (!did_set) {
+        std.log.warn("did not set viewport!", .{});
+    }
+}
+
 pub fn main() !void {
     var gp_allocator = std.heap.GeneralPurposeAllocator(.{}){};
     const alloc = gp_allocator.allocator();
@@ -118,6 +130,7 @@ pub fn main() !void {
     win.setUserData(&state);
 
     win.setActiveCallback(handleActive);
+    win.setResizeCallback(handleResize);
 
     var buf = try Buffer.init(alloc, Width, Height);
     defer buf.deinit();