screen: refactor arg order and fix some math

Signed-off-by: Tim Culverhouse <tim@timculverhouse.com>

examples/main.zig

@@ -33,16 +33,16 @@ pub fn main() !void {
                 }
             },
             .winsize => |ws| {
-                try vx.resize(alloc, ws.rows, ws.cols);
+                try vx.resize(alloc, ws);
             },
             else => {},
         }
 
         const win = vx.window();
-        const child = win.initChild(20, 20, .expand, .expand);
+        const child = win.initChild(win.width / 2 - msg.len / 2, win.height / 2, .expand, .expand);
         for (msg, 0..) |_, i| {
             const cell: Cell = .{ .char = .{ .grapheme = msg[i .. i + 1] } };
-            child.writeCell(cell, i, 0);
+            child.writeCell(i, 0, cell);
         }
         try vx.render();
     }

src/Screen.zig

@@ -3,6 +3,8 @@ const assert = std.debug.assert;
 
 const Cell = @import("cell.zig").Cell;
 
+const log = std.log.scoped(.screen);
+
 const Screen = @This();
 
 width: usize,
@@ -22,6 +24,7 @@ pub fn deinit(self: *Screen, alloc: std.mem.Allocator) void {
 }
 
 pub fn resize(self: *Screen, alloc: std.mem.Allocator, w: usize, h: usize) !void {
+    log.debug("resizing screen: width={d} height={d}", .{ w, h });
     alloc.free(self.buf);
     self.buf = try alloc.alloc(Cell, w * h);
     for (self.buf, 0..) |_, i| {
@@ -32,7 +35,7 @@ pub fn resize(self: *Screen, alloc: std.mem.Allocator, w: usize, h: usize) !void
 }
 
 /// writes a cell to a location. 0 indexed
-pub fn writeCell(self: *Screen, cell: Cell, row: usize, col: usize) void {
+pub fn writeCell(self: *Screen, col: usize, row: usize, cell: Cell) void {
     if (self.width < col) {
         // column out of bounds
         return;
@@ -41,7 +44,7 @@ pub fn writeCell(self: *Screen, cell: Cell, row: usize, col: usize) void {
         // height out of bounds
         return;
     }
-    const i = (col * self.width) + row;
+    const i = (row * self.width) + col;
     assert(i < self.buf.len);
     self.buf[i] = cell;
 }

src/Window.zig

@@ -3,6 +3,8 @@ const std = @import("std");
 const Screen = @import("Screen.zig");
 const Cell = @import("cell.zig").Cell;
 
+const log = std.log.scoped(.window);
+
 const Window = @This();
 
 pub const Size = union(enum) {
@@ -59,9 +61,10 @@ pub fn initChild(
 }
 
 /// writes a cell to the location in the window
-pub fn writeCell(self: Window, cell: Cell, row: usize, col: usize) void {
+pub fn writeCell(self: Window, col: usize, row: usize, cell: Cell) void {
+    if (self.height == 0 or self.width == 0) return;
     if (self.height < row or self.width < col) return;
-    self.screen.writeCell(cell, row + self.y_off, col + self.x_off);
+    self.screen.writeCell(col + self.x_off, row + self.y_off, cell);
 }
 
 test "Window size set" {

src/vaxis.zig

@@ -3,6 +3,7 @@ const std = @import("std");
 const Queue = @import("queue.zig").Queue;
 const ctlseqs = @import("ctlseqs.zig");
 const Tty = @import("Tty.zig");
+const Winsize = Tty.Winsize;
 const Key = @import("Key.zig");
 const Screen = @import("Screen.zig");
 const Window = @import("Window.zig");
@@ -91,8 +92,8 @@ pub fn Vaxis(comptime T: type) type {
         /// resize allocates a slice of cellsequal to the number of cells
         /// required to display the screen (ie width x height). Any previous screen is
         /// freed when resizing
-        pub fn resize(self: *Self, alloc: std.mem.Allocator, w: usize, h: usize) !void {
-            try self.screen.resize(alloc, w, h);
+        pub fn resize(self: *Self, alloc: std.mem.Allocator, winsize: Winsize) !void {
+            try self.screen.resize(alloc, winsize.cols, winsize.rows);
         }
 
         /// returns a Window comprising of the entire terminal screen
@@ -124,7 +125,6 @@ pub fn Vaxis(comptime T: type) type {
         }
 
         pub fn render(self: *Self) !void {
-            log.debug("HERE", .{});
             var tty = self.tty orelse return;
 
             _ = try tty.write(ctlseqs.home);